1. Motion, Forces and Energy Flashcards
What are rulers used for?
To measure small distances
What unit are rulers able to measure to?
mm
What is the accuracy of a ruler?
0.1 cm
What is a micrometer screw gauge used for?
To measure very small distances that a ruler cannot
What unit is a micrometer screw gauge able to measure to?
mm
What is the accuracy of a micrometer screw gauge?
0.01 mm
What are vernier calipers used for?
To measure very small distances that a ruler cannot
What unit are vernier calipers able to measure to?
mm
What is the accuracy of a vernier caliper?
0.02 mm
When measuring very small distances which apparatus is most appropriate?
Micrometer screw gauge
What is used to measure large distances?
Tape measure
What unit is a tape measure able to measure to?
m
What is used to measure very large distances?
Trundle wheel
What unit is a trundle wheel able to measure to?
m
What is used to measure volume?
Measuring cylinder
What 2 things does measure cylinder measure?
- Volume of a liquid
- Volume of an irregular-shaped object
What are used to measure intervals of time
Stop-clocks and stopwatches
How do you measure things that would be difficult to get accurate readings?
- Measure multiples
- Average
Define speed
Change in distance per unit time
What is the formula for speed?
Distance ÷ time taken
Define velocity
Displacement per unit time
What is the formula for velocity?
Displacement ÷ time taken
Define acceleration
Change in velocity per unit time
What is the formula for acceleration?
Change in velocity ÷ time taken
What does the gradient of a distance-time graph represent?
Speed
What does the gradient of a speed-time graph represent?
Acceleration
What does the area underneath a speed-time graph with constant acceleration represent?
Distance
What is deceleration?
Negative acceleration
What is the acceleration of free fall for a body near to the Earth?
Constant at 10 m/s
What is mass?
The amount of matter contained in an object
What is weight?
A gravitational force
What is the unit of mass?
kg
What is the unit of weight
N
What does mass resist?
Change in motion or change in direction
What is the resistance to change in motion or change in direction by mass called?
Inertia
What is the effect of a gravitational field on a mass?
Weight
Exam tip ; )
- In the absence of air resistance, all objects fall with the same acceleration, regardless of their mass
- So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for.
Describe terminal velocity
- There is a downwards unbalanced force and the skydiver accelerates
- As the skydiver speeds up, the air resistance increases
- Eventually the air resistance balances the weight and so the skydiver travels at a constant speed
- When the parachute is opened the increase air resistance on the parachute creates an upwards unbalanced force, making the parachuting to slow down
What term is used when air resistance and weight cause a body to move at constant speed?
Terminal velocity
How can weight (and hence mass) be compared?
Using a balance
What is the formula for density?
ρ = mass ÷ volume
Which object will float based on density?
The less dense object will float on a more dense object
What are 3 effects of forces?
Change in size
Change in motion
Change in direction
What is Hooke’s Law?
The extension of a spring is proportional to the applied force
What is the formula for Hooke’s Law?
F = kx
*where k is the spring constant
What is the limit of proportionality?
Point at which load and extension are no longer proportional
What is the elastic limit?
Point at which the spring will no longer return to its original position after being stretched
What is the formula for force?
F = ma
Exam tip ; )
A relationship is said to be proportional if the graph is a straight line going through the origin.
If a graph is a straight line but does not go through the origin the relationship is said to be linear.
Describe circular motion
An object at steady speed in circular orbit is always accelerating as it’s changing direction but gets no closer to the center
What quantity stays constant for circular motion?
Speed
What causes circular motion
A force acting at 90 degrees to an object’s direction of travel
Which factors affect the force needed to make something follow a circular path?
Mass
Speed
Radius
How does mass affect force that makes an object follow a circular path?
A greater mass requires greater force
How does speed affect force that makes an object follow a circular path?
A greater speed requires greater force
How does radius affect force that makes an object follow a circular path?
A greater radius requires greater force
What is centripetal force?
A force acting towards the centre of a circle
What is the result of a body not having a resultant force?
- Continues to travel at constant speed in a straight line
- Stays at rest
What is friction?
The force between two surfaces which impedes motion and results in heating
What is a form of friction?
Air resistance
What is a moment ?
A measure of the turning effect of a force
What increases the moment of a force?
- Increasing force
- Increasing distance from a pivot
What is the formula for moment?
Nm = Force × perpendicular distance from the pivot
What is the principle of moments?
For a system to be balanced, the sum of clockwise moments must be equal to the sum of anticlockwise moments
What are 2 conditions for equilibrium?
- No resultant force
- No turning effect
What is the centre of mass?
The point through which the weight of an object acts
Where is the centre of mass of a symmetrical object found?
The point of symmetry
Describe an experiment to find the centre of mass of a plane lamina
Make a hole in the lamina
Hang it so it can swing freely
Hang a plumb line in the hole
Use a pencil to draw a vertical line from the pivot
Repeat the process, suspending the object from a different point
Centre of mass is locating where the lines cross
When is an object stable?
When its centre of mass lies above its base
When is an object unstable?
When its centre of mass does not lie above its base
How does an object’s centre of mass affect its stability?
A lower centre of mass will make the object more stable
What can an object’s stability be increased?
- Increase surface area
- Make the object shorter
What is a scalar?
A quantity with only magnitude
What is a vector?
A quantity with both magnitude and direction
What are 4 examples of scalar quantities?
Distance, time, energy and mass
What are 4 examples of vector quantities?
Acceleration, momentum, displacement and force
How do you find the resultant vector when 2 vectors point to different direction?
Draw an arrow representing the first vector
Starting at the tip of the first vector, draw an arrow representing the second vector
Resultant vector is found by going from the tail of the first vector to the tip of the second vector
What is the formula for momentum?
p = mass × velocity (or) mv
What are 2 formulas for impulse?
- impulse = force × time
- impulse = change in momentum / Ft = mv - mu
What is the principle for the conservation of momentum?
In the absence of external forces, the total momentum of a system remains the same
Give 6 examples of energy
Kinetic
Gravitational potential
Internal
Elastic (strain)
Chemical
Nuclear
What is the formula for kinetic energy?
kinetic energy = 0.5mv^2
What is the formula for gravitational potential energy?
gravitational potential energy = mg∆h
What is the principle of conservation of energy?
Energy cannot be created or destroyed, it can only change from one form to another
Bonus question
What is energy?
The capacity of something to do work
What are 4 ways in which energy is transferred during processes and events?
Forces (mechanical working)
Electrical currents (electrical working)
Heating
Waves
What 3 forms of energy end up dissipating?
Heat, sound and light
Describe how electricity is obtained from fuels
Fuels are burnt to produce heat
Heat is used to convert water into steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained from water
Hydroelectric and tidal power use GPE of water
This turns turbines
Turbines generate electricity
Describe how electricity is obtained from waves
- Kinetic energy of waves is used to turn turbines
- Turbines generate electricity
Describe how electricity is obtained from geothermal resources
Heat from underground rocks used to generate steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained by nuclear fission
Uranium atoms split by firing neutrons at them
Releases heat used to generate steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained from light from the Sun
Photovoltaic cells use light to generate electricity
Describe how electricity is obtained from heat from the Sun
Heat is used to warm water moving through black pipes
Steam is produced to turn turbines
Turbines generate electricity
Describe how electricity is obtained from wind
- Kinetic energy of wind used to turn wind turbines
- Wind turbines generate electricity
What are the advantages of using chemical energy stored in fuel to generate electricity?
Cost-effective
Produce energy on a large-scale
Reliable
What are the disadvantages of using chemical energy stored in fuel to generate electricity?
- Produces greenhouse gases
- Non-renewable
What are the advantages of using water to generate electricity?
Renewable
No greenhouse gases produced
Produces energy on a large-scale
Hydro is reliable
What are the disadvantages of using water to generate electricity?
- Expensive to build
- Tidal is not reliable
What are the advantages of geothermal resources used to generate electricity?
- Reliable
- Cost-effective
What are the disadvantages of geothermal resources used to generate electricity?
- Does not produce energy on a large-scale
- Produces greenhouse gases
- Non-renewable
What are the advantages of generating electricity by nuclear fission?
- Reliable
- Produces energy on a large-scale
- No greenhouse gases produced
What are the disadvantage of generating electricity by nuclear fission?
- Produces radioactive waste
- Expensive to build
What are the advantages of using heat and light from the Sun to generate electricity?
- Renewable
- No greenhouse gases produced
What are disadvantages of using heat and light from the Sun to generate electricity?
- Unreliable
- Does not produce energy on a large-scale
- Expensive to set up
Which 3 energy resources is the Sun not a source of?
- Geothermal
- Nuclear
- Tidal
Which 3 energy resources is the Sun not a source of?
- Geothermal
- Nuclear
- Tidal
By what process does the Sun release energy?
Nuclear fusion
What is efficiency?
How much useful work is done from the total energy supplied
What is the formula for efficiency in terms of energy?
Efficiency = useful energy output ÷ total energy input
What is the formula for efficiency in terms of power?
Efficiency = useful power output ÷ total power input
What is work done equal to?
Energy transferred
What 2 things are used to calculate work done?
- Magnitude of the force
- Distance moved in the direction of the force
What is the formula for work done?
W = Fd = ∆E
What is the unit for work done?
Joules (J) or Newtonmetres (Nm)
What is power?
Amount of energy transferred per second
What is the formula for power?
P = ∆E/t
What does kilo mean?
1,000
What does mega mean?
1,000,000
What does giga mean?
1 billion
What is pressure?
The concentration of a force
What is the formula for pressure?
p = F/A
What is used to measure atmospheric pressure?
Mercury barometer
What is used to measure pressure difference?
Manometer
What does the height difference show?
Extra pressure the gas supply has
What is the formula of pressure in liquids?
p = hρg
What are 2 factors of pressure in liquids?
- Depth of the liquid
- Density of the liquid
State Boyle’s Law?
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to volume
What is the difference between the force upthrust and reaction force?
Up thrust is created when an object displaces a fluid, such as a boat displacing water.
Reaction force is the upward force on a block which is resting on a solid surface.
What is the SI unit for force?
newton or N
What type of force is created between two magnets?
magnetic force
This force can be attractive or repulsive
If a person has a mass of 100 kg on Earth. What will their weight be?
The gravitational field strength of the Earth is 10 N/kg
W=mg
W = 100 kg x 10 N/kg
W = 1000 N
What feature of a velocity-time graph gives the acceleration?
gradient of velocity-time graph
Masses are attracted to each other. Planets are attracted to each other. Name the force acting between them.
Gravitational force
Describe what is happening in a distance-time curve graph and explain how you know.
The object is accelerating or speeding up from the starting position
The gradient of the line is increasing, therefore velocity is increasing.
Which distance-time straight line gradient represents a faster velocity?
More steep line
Object is covering more distance per time
If an object has a 50 N force acting North and a 50N force acting south, what is the resultant force?
50 N - 50 N = 0
What is the SI unit for displacement or distance travelled?
metre or m
F= ma
Make acceleration the subject of the equation
a = F/m
Which of the following quantities are vectors?
mass
acceleration
force
speed
velocity
time
acceleration
force
velocity
In which part of the graph is the object moving the fastest?
gradient of the line is the steepest
more distance covered per time
faster speed
In which part of the graph is the object travelling back to the start.
-gradient of the line is negative
-velocity is negative
-travelling in opposite direction to part A
What is the equation for average speed?
average speed = total distance travelled/ time taken
What type of force acts forward on a rocket?
Thrust
Thrust is created when an object throws something out in one direction- such as gases.
What type of force is reduced if an object is streamlined?
air resistance
Rockets can push gas out and downward and the rocket moves upward. What is the name of this upward force on the rocket?
Thrust
What feature of a velocity-time graph gives the acceleration?
gradient of velocity-time graph
What feature of a velocity-time graph gives the distance travelled?
area under a velocity-time graph
In which graph, the object is decelerating?
in the graph, that gradient is getting less steep
What can forces do to an object?
change the speed of the object (accelerate or decelerate)
change the direction of the object
change the shape of the object
A horizontal line on a velocity-time graph shows?
constant velocity, no acceleration
A horizontal line on a distance-time graph shows what?
That the object is not moving, has zero speed
If a book is a rest on a table, what two forces are acting on it.
downward gravitational pull (or weight)
upward reaction force from table
If an object accelerates at 10 m/s2. How fast would it be travelling after 10 s if it started at rest?
It will gain 10 metres per second every second.
After 10 s if should be travelling at 100 m/s!
What feature of a distance-time graph gives the velocity?
gradient of distance-time graph
What can be done to reduce friction when an object is sliding on a surface?
use oil or grease on the surfaces
make the surfaces smoother
blow air between the surfaces
In which part of a graph is the object stopped?
Gradient that is zero therefore speed is zero- object is not moving
What type of force acts upward on the wing of an aeroplane?
Lift
What is the SI unit for acceleration?
metre per second squared or m/s2
In the equation W=mg, what is g (gravitatinal field strength or gravity) measure in?
gravity g is measure in N/kg
It is the force which acts on every kg of mass
Describe what is happening to the velocity in this distance time graph.
can’t add images thus imagine yourself ; )
A –> B velocity is constant
B –> C velocity is zero
C –> D velocity is increasing
D –> E velocity is zero
E–> F velocity is constant but opposite direction
F= ma
Make mass the subject of the equation
m = F/a
What is used to measure force?
A force meter
define acceleration
Acceleration is the rate of change of speed
OR
The change in speed per unit time
In which part of a graph object travelling at a constant speed?
in the graph the gradient is constant throughout
In which part of a graph object travelling at a constant speed?
Name three scalar quantites
time
mass
speed
distance
energy
What is the equation which links weight, mass and gravitational field strength?
Weight = mass x gravitational field strength
W = mg
How would you sketch a d-t graph of an object accelerating away from a point
The gradient of the line is increasing
speed is increasing
object is accelerating
What is the SI unit for time?
seconds or s
What is Newton’s second law?
F = ma
An object will accelerate or decelerate if an unbalanced force is acting on it.
F is the resultant force
What force is created in the rope of a swing?
tension
This upward force on an object is equal the weight of the fluid (water) the object displaces. Name the force.
Up thrust
What does a ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What does a ticker tape show about the movement of the object?
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What is the SI unit for velocity or speed?
metre per second or m/s
What is the SI unit for velocity or speed?
metre per second or m/s
In which part of the graph is the object decelerating?
gradient is getting less steep
What type of force is created between two charged particles?
electrostatic force
This can be attractive or repulsive
What is the difference between a vector and scalar quantity?
scalar quantities have magnitude only
vector quantites have both magnitude and direction
How do you find the instantaneous speed from a distance time graph?
Calculate the gradient of the line at that instant.
Draw a triangle and calculate
speed = rise/ run - distance travelled/ time
What feature of a distance-time graph gives the velocity?
gradient of distance-time graph
If a person has a mass of 100 kg on Earth. What will their weight be?
The gravitational field strength of the Earth is 10 N/kg
W=mg
W = 100 kg x 10 N/kg
W = 1000 N
speed =distance / time
rearrange for distance or d
distance = speed x time
What does this ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are moving further apart
object is cover more distance per unit time
object is speeding up, accelerating
What does this ticker tape show about the movement of the object?
dots are moving further apart
object is cover more distance per unit time
object is speeding up, accelerating
How is mass different from weight?
Mass is the amount of matter an object is made of
(measured in kg or g)
Weight is the gravitational pull on the object which depend on the gravitational field strength of the planet
(measured in Newtons or N)
Why does the moon have less gravity (or gravitational field strength) than the Earth?
The moon has less mass than the Earth
If a person has a mass of 100 kg on Earth. What will their mass be on the moon?
The gravitational field strength of the moon is 1/6th that of the Earth
100 kg
Mass the amount of matter an object is made of. It does not change when on another planet
What does this ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What does this ticker tape show about the movement of the object?
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
Which ticker tape shows an object which is decelerating then accelerating?
can’t add images thus imagine yourself ; )
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
Which ticker tape shows an object which is decelerating then accelerating?
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
Which ticker tape shows an object which is decelerating?
can’t add images thus imagine yourself ; )
dots get closer together
object is covering less distance per unit time
object is slowing down
If a person has a weight of 600N on Earth. What will their mass and weight be on the moon?
The gravitational field strength of the Earth is 10 N/kg*
Gravity on the moon is 1/6 th the gravtity on Earth*
Weight will be 1/6th that on the Earth which is 100N
To calculate mass on Earth
W= mg
m = W/g
mass = 600 / 10 = 60 kg
Mass on the moon is the same- 60kg
In which part of the graph is the object at rest?
gradient is zero
What is the relationship between force, mass and acceleration?
Force = mass x acceleration
F = ma
This is called Newton’s second law
F= ma
Make mass the subject of the equation
m = F/a
F= ma
Make mass the subject of the equation
m = F/a
What does this ticker tape show about the movement of the object?
dots are moving further apart
object is covering more distance per unit time
object is speeding up, accelerating
In which part of a graph is the object stopped?
Gradient is zero therfore speed is zero- obejct is not moving
What is the unit for acceleration?
m/s^2
What type of force is created between two magnets?
magnetic force
Which ticker tape shows an object which is decelerating then accelerating?
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
I am a type of force that is created from a fluid being displaced.
What force am I?
Up thrust
speed = distance /time
rearrange for time or t
time = distance / speed
What is the equation for acceleration?
a = (v-u)/t
OR
a = change in velocity / time
Why are arrows perfect for drawing forces (a vector) quantities?
The arrow length can represent the magnitude of the force. The arrow direction can represent the direction the force is acting in.
If a person has a mass of 100 kg on Earth. What will their mass be on the moon?
The gravitational field strength of the moon is 1/6th that of the Earth
100 kg
Mass the amount of matter an object is made of. It does not change when on another planet
If an object is decelerating at 2 m/s2, how fast is it going after 4 seconds if it was travelling at 14 m/s?
It will lose 2 metres per second every second.
after 4 seconds it will decrease its velocity by 8 m/s
14 - 8 = 6 m/s
Define density
the mass per unit volume
How do you measure volume accurately when using a measuring cylinder?
Read the volume at eye level and to the bottom of the meniscus
place measuring cylinder on a level surface
What is the unit for density?
g/cm^3 or kg/m^3
Which orientation of the block below would create in a smaller pressure on a table?
First orientation
P = F/A
The second block has a larger area in contact with the table, for the same force, therefore, the pressure is lower
How can the volume of an irregular object be found using a measuring cylinder?
- Half fill measuring cylinder with water and read initial volume at eye level and bottom of the meniscus
- lower object into measuring cylinder- make sure that it is fully submerged and water level has not risen above the scale
- read final volume at eye level and bottom of the meniscus
- Volume of object = final volume - initial volume
The second object has half the mass but the same volume, How does its density compare to the first object?
density = mass / volume
if mass is double for the same volume, the density doubles.
density is proportional to mass
How could you find the density of a paperclip accurately?
- measure the mass of 50 paperclips on a balance
- half fill a measuring cylinder with water and record initial volume
- carefully add 50 paperclips and record final volume.
- calculate the volume by taking the difference
- Find density = mass / volume
What is a pascal?
1 Pascal = 1 Newton per metre square
How do you find the density from a mass vs volume graph?
calculate the gradient
gradient = rise/run = mass/volume
Explain what design feature makes a knife able to cut easily.
A sharp knife with a small surface area creates a greater pressure for the same force.
pressure = force/area
The knife will cut more easily
What equation links density, mass and volume?
ρ = mass ÷ volume
What equation links density, mass and volume?
ρ = mass ÷ volume
What is the unit for force?
Newton or N
Camels have adapted to walk effortlessly in the desert sand. Explain
Camels feet have a large surface area
P = F/A
A larger surface area for the same force results in lower pressure
The camel will not sink as much in the sand and can walk more easily.
How can the volume of an irregular object be measured accurately using a Eureka can?
- overfill eureka can with water and wait for water to stop dripping from the spout
- hang object from a string and slowly lower the object into the water
- make sure that the object is fully submerged
Which orientation of the block below would create a larger pressure on a table?
can’t add images thus imagine yourself ; )
Second orientation
P = F/A
The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher
Which orientation of the block below would create a larger pressure on a table?
Second orientation
P = F/A
The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher
What is the unit for volume?
m3
If a block of wood is cut in half, how does the density of the original block compare with the new half blocks?
Their densities are the same.
Both the mass and the volume were halved.
Which dam must withstand a larger pressure?
can’t add images thus imagine yourself ; )
The pressure on both dams is the same since the depth of water is the same
What is the unit for pressure?
Pascal (Pa)
What is the unit for pressure?
Pascal (Pa)
What is the equation that links pressure, density of a fluid, gravity and depth?
What is the equation that links pressure, density of a fluid, gravity and depth?
p = ρgh
Which section A, B, C, D or E experiences the largest pressure?
can’t add images thus imagine yourself ; )
P = density x gravity x depth
All the sections experience the same pressure since the depth of water is the same.
Pressure at depth is not affected by the volume of water- only the depth of water above it.
How does the density vary between ice and sea water?
Ice has less particles per unit volume
ice has a lower density
Ice floats on sea water
How can mass be measured accurately?
placed balance on level surface
tare (zero) balance before use
How does the pressure vary with depth in the ocean?
As depth double, pressure doubles.
Pressure is proportional to depth
The graph is a straight line through the origin.
What is the unit for mass?
kg
always convert grams to kilograms
Fluid pressure acts in all directions.
What causes air pressure?
Air particles move in all directions and collide with objects
Air particles move fast and freely
Air pressure is related to the depth of air over the object.
What is the unit for area?
m^2 or cm^2
What equation links pressure, force and area?
P = F/A
Which object has the largest density in a mass-volume graph?
Object that has more mass per unit volume - the gradient is steeper
Which object below would have the highest density values?
can’t add images thus imagine yourself ; )
First object
Greater mass per unit volume
The particles are more closely packed
Which object below would have the highest density values?
First object
Greater mass per unit volume
The particles are more closely packed
If spring A is a single spring, spring B must be..
1) stiffer spring
2) weaker spring
can’t add images thus imagine yourself ; )
Answer: 2) weaker spring
B has a smaller gradient
It requires less force to stretch by the same amount.
Why is a double decker bus difficult to tip?
It has a low centre of gravity
The weight acts from the centre of gravity.*
It will not tip until the weight goes beyond the base*
Below is a velocity-time graph for a parachute jump.
What portion/s of the graph represents the constant speed? How do you know?
can’t add images thus imagine yourself ; )
portion c and e
The velocity is constant. The graph is horizontal at c and e
gradient is zero = zero acceleration or constant speed
The parachutist has reached terminal velocity at c and again at e (after he opens his parachute)
How do you find the centre of gravity for a symmetrical object?
Draw lines of symmetry to find the centre of the object.
Below is a force extension graph for a wire. Does the wire obey Hook’e Law?
can’t add images thus imagine yourself ; )
The wire obeys Hooke’s Law during the straight part of the graph. If the force were removed, the wire behaves elastically and would go back to its original length.
For larger forces the wire no longer obeys Hooke’s Law, the wire behaves plastically and will not go back to its original length.
Define thinking distance
Thinking distance is the distance a car travel after you see the hazard to the point you put your foot on the brake - the distance travelled while you are reacting to the hazard
Why does the swinging basket finally come to rest?
can’t add images thus imagine yourself ; )
Swung to one side, the line of the weight (the force) does not act through the pivot at the top of the hanger. M= F x d, there is a moment about the pivot making it swing.
When at rest the line of the weight (the force) acts through the pivot at the top of the hanger. M = F x d. there is no moment about the pivot. No longer swings.
What is the Centre of Gravity?
The point on an object where the weight appears to act.
If one spring needs 5 N to stretch 10 cm. How far would this spring system stretch with 5 N pulling on it?
can’t add images thus imagine yourself ; )
There are three springs in the series system. Each spring will stretch 10 cm. The total stretch of the series spring system would be 30 cm.
What factors affect thinking distance of a vehicle?
tiredness
drinking or drug taking
speed of vehicle
distractions such as mobile phone
Define braking distance
The distance a vehicle travels while the brakes are applied and the vehicle comes to rest.
How can the elephant balance on the ball?
The centre of gravity of the elephant is located over the ball
The weight of the elephant passes through the ball (base)
There is no perpendicular distance to the pivot and no moment (turning effect)
How do you find the stopping distance from thinking distance and braking distance?
stopping distance = thinking distance + braking distance
If the speed of a vehicle doubles, what happens to the braking distance?
As speed double the braking distance more than doubles- it actually quadruples!
If the single spring needs 2 N to stretch 10 cm, how many centimetres will the series spring system stretch with the same force?
can’t add images thus imagine yourself ; )
There are two springs in series with 2 N hanging on them. They will both stretch by 10 cm.
The overall stretch will be 20 cm.
If the single spring needs 2 N to stretch 10 cm, how many centimetres will the series spring system stretch with the same force?
There are two springs in series with 2 N hanging on them. They will both stretch by 10 cm.
The overall stretch will be 20 cm.
Which spring is stiffer or has the greater spring constant?
can’t add images thus imagine yourself ; )
Spring A needs more force to stretch the same distance as spring B.
Gradient for spring A is greater.
What is the equation that links moment, force and perpendicular distance?
Moment = force x perpendicular distance
What factors affect braking distance of a vehicle?
tread depth of tyres
icy or wet roads
mass of vehicle
condition of brakes
speed of vehicle
What is the principle of moments?
For an object to be in equilibrium
sum of the clockwise moments must equal the sum of the anticlockwise moments
What is the relationship between weight, mass and acceleration?
W = mg
Weight = mass x acceleration
Below is a force vs spring length graph for a spring.
a) What is the original length of the spring?
b) What is the extension at 4 N?
can’t add images thus imagine yourself ; )
Read the length at 0 N
Therefore the original length is 15.0 cm
extension = length - original length.
extension = 40.0 - 15.0 = 25.0 cm
Below is a force vs spring length graph for a spring.
a) What is the original length of the spring?
b) What is the extension at 4 N?
Read the length at 0 N
Therefore the original length is 15.0 cm
extension = length - original length.
extension = 40.0 - 15.0 = 25.0 cm
How do you find the centre of gravity of a lamina?
1- punch three holes along edge of the lamina
hang the lamina on a horizontal pin in a cork
hang plumbline infront of lamina
let the lamina and plumbline come to rest
mark plumbline position down the lamina
repeat for other two holes.
centre of gravity is located where all three lines cross.
What will happen to an object if its total anticlockwise moments do not equal the total clockwise moments?
The object will turn
Moment is a vector quantitiy and there will be a resultant moment
Below is a velocity-time graph for a parachute jump.
Describe what happens to the
acceleration from a to c
can’t add images thus imagine yourself ; )
The gradient of the graph is decreasing.
gradient of a v-t graph is the acceleration
acceleration is decreasing
The anticlockwise moment acting the beam below is calculated by
M = F x perpendicular d
M = 15N x 0.2m = 3 Nm
Why was the distance 0.2 m used?
0.2 m is the perpendicular distance to the line of force.
OR
0.3 m is not perpendicular to the force
If the speed of a vehicle is doubled, what happens to the thinking distance.
As speed doubles, thinking distance doubles- you cover double the distance in the same reaction time.
What equipment is needed to study how the force on a spring affects its extension?
How would this be carried out accurately?
read the length of the spring at eye level to avoid a parallax error
allow spring to stop bouncing up and down before taking reading.
repeat readings AND take an average by taking readings as the spring is loaded then again as it is unloaded- do not go beyond its elastic limit.
Below is a force-extension graph for a spring.
(a) In which portion of the graph does the spring obey Hooke’s Law?
(b) Where is the elastic limit (E) of the spring- where the spring would be permanently deformed?
can’t add images thus imagine yourself ; )
The straight region of the graph shows that the force is proportional to the extention. Therfore, it obeys Hooke’s Law
If the spring is stretched beyond the elastic limit it would no longer go back to its original length.
Below is a force-extension graph for a spring.
(a) In which portion of the graph does the spring obey Hooke’s Law?
(b) Where is the elastic limit (E) of the spring- where the spring would be permanently deformed?
The straight region of the graph shows that the force is proportional to the extention. Therfore, it obeys Hooke’s Law
If the spring is stretched beyond the elastic limit it would no longer go back to its original length.
Below is a velocity-time graph for a parachute jump.
What portion/s of the graph represents the greatest deceleration?
can’t add images thus imagine yourself ; )
portion d
The velocity is decreasing at d and the gradient is very steep representing a very large deceleration.
How would you investigate how the force on a wire affects its extension?
wire must be over 1 metre
attach tape to wire with a pen line- read length at eye level
add mass carefully to wire without pulling on it
A moment is the turning effect of a force. what factors affect the turning force?
The force exerted
The perpendicular distance between the line of action (force) and the pivot.
Moment = Force x perpendicular Distance
If the single spring needs 6 N to stretch 20 cm, how much force must hang on the parallel spring system to stretch it by the same amount (20 cm)?
can’t add images thus imagine yourself ; )
There are two springs in parallel. Each spring needs 6N to stretch 20 cm. The overall force needed is 12 N to stretch the parallel system 20 cm
List these people in order of stability.
Greatest to the least stable
Boy > teenager > woman > man
The man has the highest centre of gravity*
The boy has the lowest centre of gravity*
If a spring stretches by x centimeters with 1N hanging on it. How far will it stretch with 2N?
The spring will stretch 2x centimetres.
Springs obey Hooke’s Law.*
If force is doubled, extension doubles.*
Force is proportional to extension*
What force is needed to balance the beam?
M clockwise = 200 N x 40 cm = 800 Ncm
To be at equilibrium, sum of clockwise moments must equal the sum of the anticlockwise moments
M anticlockwise = F x 100 cm = 800 Ncm
Force of 8 N needed!!
What force is needed to balance the beam?
can’t add images thus imagine yourself ; )
M clockwise = 5 N x 0.5 m = 2.5 Nm
To be at equilibrium, sum of clockwise moments must equal the sum of the anticlockwise moments
M anticlockwise = F x 0.25 = 2.5 Ncm
Force of 10 N needed!!
Below is a velocity-time graph for a parachute jump.
Explain the change in
acceleration from a to c
can’t add images thus imagine yourself ; )
at the start- only downward weight is acting on the person. Large resultant force downward. F=ma, large force –> more acceleration
as speed increases at b, air resistance increases. Resultant force is smaller, F=ma, smaller force, less acceleration
at c- upward air resistance = downward weight. Forces are balanced. Resultant force = zero, F=ma, no resultant force, no acceleration- constant speed and terminal velocity has been reached
Which exerted force (A, B or C) will create the largest moment (or turning effect) on the door?
can’t add images thus imagine yourself ; )
B
It has the largest perpendicular distance to the pivot.
Moment = Force x perpendicular distance to the pivot
Both A and C have a zero perpendicular distance to the pivot
Does a rubber band obey Hooke’s Law?
How do you know?
can’t add images thus imagine yourself ; )
The force extension graph for the rubber band is not a straight line through the origin.
Force is not proportional to extension
It does not obey Hooke’s Law
Does a rubber band obey Hooke’s Law?
How do you know?
The force extension graph for the rubber band is not a straight line through the origin.
Force is not proportional to extension
It does not obey Hooke’s Law
The graph below is the force-extension graph for a spring. Explain how you know that the spring obeys Hooke’s Law.
can’t add images thus imagine yourself ; )
The force-extension graph is a straight line through the origin.
As the force doubles the extension doubles
Force is proportional to extension
How are velocity, displacement and time related?
velocity = displacement/ time
Is moment (turning effect) a vector or scalar quantity?
vector quantity
direction matters!!
A clockwise moment can cancel an anticlockwise moment.
Describe the properties of heat radiation.
it travels in straight lines
it can travel through a vacuum
it can reflect off surfaces
it is an electromagnetic wave much like light
it travels at the speed of light
it is a transverse wave
Using the Sankey diagram calculate the efficiency of a thermal power station
1000 J = one large square
200 J = each small square
Useful transfer of Energy Out = 9 small squares
1800J of energy useful transferred electrically out of thermal power station
1800 J/ 5000J = (3600/ 10 000J) x 100 = 36%
Using the Sankey diagram calculate the efficiency of a thermal power station
1000 J = one large square
200 J = each small square
Useful transfer of Energy Out = 9 small squares
1800J of energy useful transferred electrically out of thermal power station
1800 J/ 5000J = (3600/ 10 000J) x 100 = 36%
Give an example of a chemical store
battery
coal- fuel
food
Give an example of a nuclear store
Uranium in a nuclear power station
Fusion occurring in the Sun
Solids are good conductors
Liquids and gases do not conduct heat well but they do convect heat easily, why?
Liquids and gases have particles which are further apart and have weak forces between them- poor conductors
Liquid and gases have particles can move freely
Convection occurs when particles gain energy (heat up) expands and move from hot to cold regions
Name the energy store depleted and filled when a roller coaster accelerates down the first slope.
Gravitational store of the roller coaster is being depleted
Kinetic store of the roller coaster is being filled along with the thermal store of the track, wheels and surroundings.
Energy is also shifted/transferred away via radiation of sound
Why are metals good conductors of heat
Conduction occurs when heat is transferred through a material from particle to particle
Metals have free electrons which help heat transfer through the metal from particle to particle
What is the law of conservation of energy?
Energy cannot be created nor destroyed, only transferred from one store to another.
Which energy store is depleted in a tidal barrage and how is it transferred away from this store?
Gravitational store of water is depleted
This is transferred mechanically to the kinetic store of the water via the force of gravity
How does heat travel from the hot stove to a potato in the water?
Conduction from the stove to the metal pan- they are in contact
Conduction through the metal pan
Conduction from the pan to the water- they are in contact
Convection to the potato- hot water expands (is less dense) and rises
Conduction through the potato
What are the disadvantages of wind power?
you need a large area and a large number to replace one power station
it is not reliable- no wind, no power
they are a danger to birds on land and boats if in the sea
they are loud and some say unsightly
Why are solids better conductors of heat than liquids and gases?
Conduction occurs when heat is transferred through a material from particle to particle
In solids, the particles are close together and the forces between particles are stronger.
What are the disadvantages of nuclear power?
non-renewable source
creates radioactive waste which takes thousands of years to decay to a safe level
expensive to build, maintain and decommission
the possibility of a meltdown causing environmental damage
Which thermometer will record the highest temperature?
The thermometer on the left nearest the matt black surface.
The hot metal radiates heat to the surroundings but the matt black surface will radiate heat at a quicker rate.
What are the advantages of coal, oil or gas power stations?
they are reliable- produce a constant supply
much of the existing infrastructure is set-up for fossil fuels
at the moment fossil fuels are relatively cheap
The thermal store of this cup of tea is depleting or emptying
How is energy transferring or shifted from this cup of tea?
by heating
What are the advantages of wind power?
renewable energy source
does not use fossil fuels
does not produce carbon dioxide or other pollutants
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Conservation of energy is energy cannot be created nor destroyed, it is only transferred from one store to another.
100kJ = Energy In
4kJ + 63kJ + ? = Energy Out
33kJ of energy goes to respiration in the cow
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Respiration = ? kJ
Eaten = 100 kJ
Tissues = 4 kJ
Faeces, urine and gas = 63 kJ
Conservation of energy is energy cannot be created nor destroyed, it is only transferred from one store to another.
100kJ = Energy In
4kJ + 63kJ + ? = Energy Out
33kJ of energy goes to respiration in the cow
How is energy shifted/transferred from the power station usefully and wastefully?
Usefully- Electrically via wires
Wastefully- Heating from furnace, wires and cooling towers
Radiated as sound from generator
Radiated as light from furnace
Give an example of a kinetic store
car, moving
spaceship, moving
bullet moving
generator turning
The fleece reduce heat loss in two ways? Explain
The fleece traps air
air is a poor conductor- reduces heat loss by conduction
air cannot move- no convection currents set up- reduces heat loss by convection
What are the disadvantages of a hydroelectric power station?
flooding of valleys and loss of habitats
can only be built in areas which are mountainous.
flooding of valleys and displacement of communities
expensive to build
How does energy transfer or shift from the chemical store of a battery to the thermal store of a bulb?
Electrically- charge moves in wires
Which container will heat up the quickest?
Matt black container vs Shiny silvery container
The matt black container
Matt black surfaces are good absorbers of heat radiation
Shiny silvery surfaces will reflect heat radiation
Give an example of a thermal store
hot pan
hot water in a kettle
the filament in a toaster
a human body
What are the 8 stores of energy?
Chemical
Thermal
Gravitational
Kinetic
Vibrational
Nuclear
Electrostatic & magnetic
Elastic
How does energy transfer or shift from a stretched elastic in a catapult to moving stone?
mechanically- elastic exerts a force on the stone
Elastic store of elastic is emptied*
Kinetic store of stone is filled*
What energy store is depleted and which energy store is filled when the popper toy is release.
How is this energy transferred from one store to another?
Elastic store of popper toy is depleted
Kinetic store of popper toy is filled
This energy is transferred mechanically via a spring force
How is energy wastefully shifted/transferred from the wind turbine
Energy is wastefully shifted/transferred from the wind turbine via radiation (sound) and heating from wires and generator
What energy store does biomass possess?
Chemical store
Give an example of electrostatic & magnetic energy store
(one of each!)
Electrostatic
Two similarly charged particles near each other
Charged van de Graaf generator
Magnetic
North and north pole of a magnet pushed together
North pole of a magnet and south pole of an electromagnet pulling in a speaker cone
What is the equation for efficiency?
Efficiency = useful energy output ÷ total energy input
Efficiency = useful power output ÷ total power input
How is energy shifted/transferred usefully from the gravitational store of the water behind the dam to a town nearby?
mechanically from gravitational store of water to the kinetic store of the water
mechanically from the turning turbine to the turning generator
electrically from the turning generator via the wires to the nearby town
How does energy transfer or shift from the nuclear store of the Sun to the chemical store of a rechargeable cell in the international space station
Via radiation through space (EM radiation)
Electrically through wires from solar cell
Give an example of gravitational store
Water behind a dam
Person at the top of a slide
Spaceship in orbit around Earth
In an experiment to test the insulating properties of different materials, what is the independent and dependent variable?
independent- I change
dependent- what you measure
Independent variable - type of material wrapped around the copper can
Dependent variable- temperature difference of water after a set amount of time
What is the difference between solar cells and solar panels?
Solar cells convert energy transferred by radiation (light) into energy transferred electrically
Solar panels convert energy transferred by radiation into the thermal store of water
How does energy transfer or shift from a stretched elastic in a catapult to moving stone?
mechanically- elastic exerts a force on the stone
Elastic store of elastic is emptied*
Kinetic store of stone is filled*
Which energy store is being depleted when the wind turbine turns?
Kinetic store of the wind
What store of energy does this boulder possess?
Gravitational store
How does energy transfer or shift from steam in a power station to kinetic store of a turbine turning?
Mechanically- there is a force on the turbine which makes it turn
In an experiment to test the insulating properties of different materials, what are the control variables
Control variables- what is kept the same to keep a fair test.
volume of water- all 100ml
initial temperature of water- all 90°C
thickness of material- all 5mm
type of can- all copper metal with the same thickness
lid- all containers have a lid of same thickness and material
same type of liquid- water
What are the advantages of a hydroelectric power station?
renewable energy source- does not use fossil fuels
does not produce CO2 or pollutants
reliable- energy transferred at a constant rate
can be turned off when not needed
the lake created behind the dam can be used for sport and recreation
How is energy shifted/transferred from the gravitational store of the rollercoaster to kinetic store of the rollercoaster as it accelerates down the slope?
Energy is shifted mechanically by the force of gravity
What energy store is being depleted in a nuclear power station?
How is this energy usefully transferred to the nearby town?
Nuclear store of the uranium is being depleted.
The energy is transferred electrically to the nearby town.
What energy store does a hot cup of tea have?
Thermal store
What energy store is depleted and which energy store is filled when the popper toy is moving upward.
How is the energy transferred from one store to another?
Kinetic store of popper toy is depleted
Gravitational store of popper is filled
Energy is transferred mechanically via the force of gravity
What are the disadvantages of a hydroelectric power station?
flooding of valleys and loss of habitats
flooding of valleys and displacement of communities
expensive to build
Using the Sankey diagram calculate the efficiency of the electric motor and the percentage the energy wasted.
Energy input =. 50 J
Energy output = 36 J
eff = useful energy out / total energy in
36J/50J = (72/100) x 100 = 72%
28% of energy is wasted as thermal store of the surroundings
What are the advantages of nuclear power?
does not produce carbon dioxide- a greenhouse gas
does not use fossil fuels
reliable continuous supply of electricity
What energy store is depleted and which energy store is filled when the popper toy is released.
How is this energy transferred from one store to another?
Elastic store of popper toy is depleted
Kinetic store of popper toy is filled
This energy is transferred mechanically via a spring force
Give an example of an elastic store
stretched elastic in a catapult
bent ruler
stretched spring in a clockwork toy
What energy store is being depleted in the Sun? How it energy transferred or shifted from the Sun?
Nuclear store is being depleted (emptied)
Energy is shifted or transferred away from the sun by radiation (infrared, visible light UV etc…)
What energy store is being depleted in the Sun? How it energy transferred or shifted from the Sun?
Nuclear store is being depleted (emptied)
Energy is shifted or transferred away from the sun by radiation (infrared, visible light UV etc…)
Thermal energy is transferred from a hot Leslie cube in three ways. There are matt black side and shiny silvery side.
Which side will radiate the most heat?
Which side will radiate the least heat?
The matt black side will radiate the most heat
The shiny silvery side will radiate the least heat
How is Sankey diagram constructed?
can’t add images thus imagine yourself ; )
using graph paper
create a scale- e.g. one small square = 10J
If Total Energy In is= 200J arrow should be 20 squares in width to start.
Useful Energy Out - straight arrow forward
5 squares = 50J
-Wasted Energy Out -arrow curling downward
15 squares = 150J
What are the advantages of tidal power?
renewable
no polluting gases produced
reliable- we know when the tides occur
saves fossil fuels
What are the advantages of wave power?
renewable
does not produce harmful gases
a free energy source
does not use fossil fuels
What are the disadvantages of wave power?
not reliable- no waves, no energy
can only be built for countries with coastal regions
a danger to boats/ships
you need a large number to replace one power station
List the four ways in which energy can be shifted or transferred
mechnically- by a force
electrically- movement of charge
radiation- light or sound
heating- hot to cold
Using ideas on convection describe how heat is transferred in a room.
air above the radiator is heated
hot air expands and becomes less dense
hot air rises and moves along the ceiling
hot air cools (becomes denser) and falls
cool air is pulled towards radiator to replace hot air which moved upward
How is the chemical store of biomass usefully transferred?
Chemical store of biomass is transferred via heating when biomass is burnt
This is mechanically transferred to a turbine which is mechanically transferred to a generator
The kinetic store of the generator turning is transferred electrically to the wires.
What are the disadvantages of solar power (solar cells)?
they are expensive
they are inefficient
they are not reliable- less sun, less power
What are the disadvantages of geothermal power
can only be built where the Earth’s crust is thin- limited places
high initial set-up costs
very high temperatures needed to produce power- need to produce steam, not just hot water.
What energy store is being depleted in a nuclear power station?
How is this energy usefully transferred to the nearby town?
Nuclear store of the uranium is being depleted.
The energy is transferred electrically to the nearby town.
Nuclear energy is being depleted in a nuclear power station
How is this energy wastefully transferred?
heating from the reactor, turbines, generator and wires
radiation of sound from turbines and generators.
What are the advantages of solar power (solar cells)?
does not use fossil fuels
renewable
does not produce carbon dioxide or other pollutants
What energy store is being filled as this hot cup of tea cools?
Thermal store of surroundings (air, table etc)
What is conduction?
Conduction occurs when heat is transferred through a material from particle to particle
Energy is stored chemically in the match.
How is energy transferred or shifted from the match?
Which energy store is being filled?
Chemical store the match is emptied.
This energy is shifted/transferred away from the match by radiation (light) and heating to the surroundings.
The thermal store of the surrounding is being filled
State the different ways in which heat is prevented from a thermos flask.
The stopper prevents heat escaping by convection.
The vacuum prevents heat escaping by conduction.
The inner flask is reflective inside, so it reduces heat lost by radiation.
The outer case protects the inner flask, and add another layer of insulation
What energy store is depleted and which energy store is filled as water rushes down the tunnels from a hydroelectric dam to the turbines below?
Gravitational store of the water is depleted and kinetic store of water is filled.
A cup with 80 C and 40 C at room temperature 30 C.
Which cup will radiate the most heat?
The cup at 80°C will radiate the most heat to the surroundings.
The greater the temperature difference the greater the rate of heat transfer.
What are the disadvantages of fossil fuel power stations?
fossil fuels are non-renewable
when they burn they release carbon dioxide which is a greenhouse gas
when they burn they produce sulfur dioxide which creates acid rain
Explain why heat transfer is reduced in the following ways.
Lid- reduces convection
Vacuum- reduces conduction
Shiny surface- reduces radiation
Lid stops heat loss by convection- lid traps air and does not allow it to move, no convection currents created which carries heat energy away
Vacuum stops heat loss by conduction- no particles means heat cannot be transferred from particle to particle through the walls to the outside
Shiny surface stops heat loss by radiation as shiny silvery surfaces reflect heat radiation back into the flask.
Which energy store is being filled as the blades accelerate and how is energy usefully shifted/transferred from the wind turbine
Kinetic store of the blades are filled
Their energy is usefully transferred mechanically to the kinetic store of the generator
Energy is usefully shifted/transferred from the generator electrically
What are the advantages of geothermal power?
it is renewable
once set-up it is free
does not produce pollutants- no harmful gases produced
What is a solar furnace?
A solar furnace consists of a large number of mirrors which reflects the sun’s radiation to one point.
At this focal point is a pipe with water. The radiative energy (light) heats the water and creates steam.
Steam turns a turbine, which turns a generator producing electricity.
What are the disadvantages of tidal power?
You need an estuary- limited places to build
it disrupts the movement of boats/fish etc..
not constant power, times of day where less power is given out
How does the heatproof mat reduce heat loss?
The heatproof mat is an insulator
It reduces heat loss by conduction to the table below
Conduction occurs when heat is transferred from particle to particle when objects are in contact.
How can forces affect objects?
Can change:
Shape
Direction of travel
Speed
What are different types of forces?
Weight
Gravitational
Friction
Air resistance (drag)
Tension
Up thrust
Reaction force
The same force is applied to two objects with different masses. Which will accelerate the most?
Lower mass object
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
What is Newton’s second law?
Resultant force= mass x acceleration
F= ma
How can friction be reduced?
Lubrication eg oil for friction
Streamlined design for air resistance
Lubrication eg oil for friction
Streamlined design for air resistance
Brakes on a car
What is an example of unuseful friction?
What is an example of unuseful friction/
What is Newton’s 3rd law?
If A exerts a force on B, then B exerts the same force on A but in the opposite direction
What is mass?
The amount of matter contained in an object
What is weight?
Force of gravity acting on an object
What is the equation involving weight, mass and gravitational field strength?
Weight = mass x gravitational field strength
W = mg
What is gravitational field strength?
Force between objects that have mass
A rocket takes off and accelerates. The rocket will use up its fuel but the thrust of the engine remains constant. How do the following change over time?
Thrust
Mass
Weight
Resultant force
Acceleration
Velocity
Thrust = constant
Mass = decrease
Weight = decrease
Resultant force = increase
Acceleration = increase
Velocity = increase
In free fall what is the only force acting?
Weight
In the absence of air resistance all objects will fall with an acceleration equal to gravity
How does air resistance change as you speed up?
Increases
What two forces act on skydivers?
weight which remains constant
- air resistance that increases with speed
What are the 3 parts of a free fall question that you have to include?
- As parachutist jumps:
- only force acting = weight
- air resistance = 0
- acceleration - Then:
- air resistance increases as speed increases
- resultant downwards force decreases (cos more upwards force)
- acceleration thus decreases - Terminal velocity:
- air resistance reaches a maximum + is equal to weight
- resultant force is 0N
- acceleration = 0
- travels at constant velocity (terminal velocity)
What are the 3 parts of a parachutist question that you have to include?
- Parachutist at terminal velocity :
- resultant force + acceleration = 0
- constant velocity - Opens chute:
- air resistance increases + resultant force is in negative direction
- thus large deceleration
- still moves down - As it slows, air resistance decreases until air resistance = weight
- resultant force = 0 and acceleration = 0
- new slower terminal velocity
What is the aim of the springs and rubber bands practical?
Investigate relationship between force and extension
Describe the method for the Hooke’s law practical
- Set up apparatus
- Record initial length of spring (should subtract this from all further measurements to find extension)
- Add 100g mass to spring
- Record mass and new length of spring
- Add another 100g mass to spring
- Record new mass and new length of spring
- Repeat
- Remove all masses and repeat 3 times and take mean average of extension
- Calculate the force by multiplying the mass x gravity
- Plot graph force x extension
What is Hooke’s law?
The extension of a spring is directly proportional to the applied load force
What does directly proportional mean?
Force extension graph will be a straight line through the origin
If the force doubles the extension doubles
Force divided by extension is constant
What is elastic behaviour of a material?
When the stretching force is removed the object will return to its original shape
What are the safety precautions?
goggles in case spring snaps
stand up so no feet are under masses
g clamp to secure clamp stand to desk so that it does not fall over
How do you calculate the spring constant?
F= kx (where F = force, k = spring constant, x = extension)
Constant= F/x (stiffness of spring)
Thus if you double the force, you double the extension (because k is always constant)
What are the possible errors of the experiment?
make sure measurements with ruler are taken at eye level to avoid parallax error
What is plastic behaviour of a material?
When the stretching force is removed the object will not return to its original shape, it will be permanently deformed
What is the gradient equal to?
The spring constant
What happens when the spring goes above the elastic limit?
wont return to its original shape
- unloading extensions will be larger than the loading extensions
What is the unit for spring constant?
N/m not Nm! Which is unit for moment
What is a moment?
Turning effect around a pivot
What is the equation involving moments?
M = Fd
Moment = force x perpendicular distance from pivot
Moment unit is Nm
What is the principal of moments?
Total clockwise moment = total anti-clockwise moment
Explain what must happen to a counterweight on a tower to keep it balanced if a larger mass was placed on the loading platform?
to make the anti clockwise and clockwise moments balanced, you should increase the weight/force of the counterweight ‘by increasing the counterweight’s mass of moving it further away from the pivot point
both would increase the moment since moment = force x perpendicular distance
What is centre of mass?
Point at which all of mass of an object could be said to act (avg position of mass)
When does an object become unstable?
when the line of action of the centre of mass passes beyond the edge of the object’s base
How can the stability of an object be increased?
Increasing size of base
(Heavy base lowers centre of gravity)
Decreasing height
Decreases toppling angle
Why does the upwards force at the right end of a plank of wood increase when object is moved towards that end?
moments about left support
as weight moves to right clockwise moment increases
perp distance between weight + pivot increases
anti-clockwise moment must increase to remain in equilibrium
to increase the anti-clockwise moment right upwards force must increase
What are renewable sources of energy?
Can be replenished by natural processes or human activity
What are non renewable sources of energy?
Cannot be replenished by natural processes/human activity - only a finite amount
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
What are the energy transfers involved in generating electricity using fossil fuels?
Coal oil /gas is burned -> chemical store of coal -> transferred by heating to thermal store of coal oil -> transferred by heating to thermal, kinetic store of water + light and sound radiation
Water turned into steam
Steam turns turbine -> kinetic store of water -> transferred mechanically to kinetic store of turbine generator -> transferred mechanically to generator
Generator generates electricity
What is biofuel?
Created over a short time span from biomass
Fossil fuels were created over hundreds of millions of years -> biofuels are carbon neutral because carbon released when burned is same as carbon used to create them
What are the energy transfers involved in nuclear power?
nuclear reactor is used to turn water into steam
nuclear store of uranium -> transferred by heating to thermal store of uranium -> transferred mechanically to kinetic store of turbine -> transferred electrically
What are the energy transfers involved in wind?
kinetic store of air transferred mechanically -> kinetic store of turbine -> transferred electrically to generate electricity
What are the energy transfers involved in hydroelectricity
gravitational store of water -> transferred mechanically -> to kinetic store of water -> kinetic store of turbine generator
What are the energy transfers involved in geothermal energy?
thermal store of rocks -> transferred by heating -> thermal store of water -> kinetic store of water -> turns to steam which turns turbine
What are the energy transfers involved in solar cells?
energy from sun transferred by radiation, solar cells transfer energy from sunlight electrically, producing a current + generating electrical power -> electrons flow
What energy transfers are involved solar heating systems?
light from sun can be used to directly heat water
this can be used to heat homes and as a hot water supply
Pros cons of fossil fuels
reliable
abundant
relatively easy to generate electricity
non renewable
fuel costs
greenhouse gases produced
acid rain
Pros cons nuclear
high energy density
no greenhouse gases
no acid rain
non renewable
expensive
production of nuclear waste
radioactive matter into environment
Biofuel pros cons
carbon neutral
renewable
-reduced fossil fuel reliance
labour intensive
large amounts of land taken up
Wind pros cons
no air pollution
renewable
cheap to run
visual pollution
expensive to build
unreliable
Pros cons water
renewable
cheap to run
no air pollution
reliable
can be turned on
damage to habitats
visual pollution
can block access to ports
trapped vegetation can produce green house gases
Pros cons solar
no air pollution
cheap
renewable
not efficient
-unreliable
what is specific heat capacity?
heat energy required to raise the temperature of a 1kg mass of a substance by one degree
equation
change in thermal energy = mass x c x change in temperature
How to find specific heat capacity of a solid?
Find mass of copper block in kg using balance
Place thermometer into smaller bore of copper block and measure initial temp of sample
Place copper block into insulating holder and place onto heatproof mat
Lubricate electrical heater with petroleum jelly and insert into larger bore in metal block
Connect electrical heater to power pack, add ammeter and voltmeter to circuit
Switch on power supply, start stopwatch - record values of voltage and current for heating circuit
Wait for temp of copper block to rise by between 20 and 30c
Switch off power supply, stop stopwatch, record time
Wait until temp on thermometer stops rising and record final temp of copper block
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
