1 Forces and Motion

Question 1

distance time graphs

Answer 1

A constant gradient represents constant speed

The gradient of the line represents the speed:
A very steep gradient means the object is moving at a large speed
A shallow gradient means the object is moving at a small speed
A flat, horizontal line means the object is stationary (not moving)

Objects might be accelerating - this is represented by a curve
In this case, the gradient of the line will be changing
If the gradient is getting steeper, the speed is increasing (accelerating)
If the gradient is getting shallower, the speed is decreasing (decelerating)

The speed of a moving object can be calculated from the gradient of the line on a distance-time graph

Question 2

speed, distance and time equation

Answer 2

speed = distance / time

Question 3

practical: investigate the motion of everyday objects such as toy cars or tennis balls

Answer 3

Measure out a height of 1.0 m using the tape measure or metre ruler
Drop the object from this height, which is the distance travelled by the object
Use the stop clock to measure how long the object takes to travel this distance
Record the distance travelled and time taken
Repeat steps 2-3 three times, calculating an average time taken for the object to fall a certain distance
Repeat steps 1-4 for heights of 1.2 m, 1.4 m, 1.6 m, and 1.8 m

Question 4

acceleration, time taken and change in velocity equation

Answer 4

acceleration = change in velocity / time taken

Question 5

velocity time graphs

Answer 5

The gradient of the line represents the magnitude of acceleration
A steep gradient means large acceleration
A shallow gradient means small acceleration
A positive gradient (upward slope) shows increasing velocity -> acceleration
A negative gradient (downwards slope) shows decreasing velocity -> deceleration
A horizontal line means the acceleration is zero so the object is moving with a constant velocity

Question 6

how to find acceleration from a velocity time graph

Answer 6

calculated from gradient of the line

Question 7

how to find the distance traveled on a velocity time graph

Answer 7

find the area under the line

Question 8

what does kg measure

Answer 8

mass

Question 9

what does N/kg measure

Answer 9

gravitational field strength or acceleration due to gravity

Question 10

what are the effects of forces between bodies

Answer 10

When a force acts on an object, the force can affect the object in a variety of ways
The object could:
change speed
change direction
change shape

Question 11

types of forces

Answer 11

Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
Electrostatic - the force between any two objects with charge (like a proton and an electron)
Thrust - the force pushing a vehicle (like the push from rocket engines on the shuttle)
Upthrust - the upward force on any object in a fluid (like a boat on the surface of a river)
Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
Compression - forces that squeeze an object (like squeezing a spring)
Tension - forces that stretch an object (like two teams in a tug-of-war)
Reaction force - the force between any two objects in contact (like the upwards force from a table on a book)

Question 12

what is the difference between vectors and scalers

Answer 12

Scalars are quantities that have magnitude but not direction
Vectors are quantities that have both magnitude and direction

Question 13

examples of vectors

Answer 13

displacement
force
weight
velocity
acceleration
momentum

Question 14

what is a force that opposes motion

Answer 14

friction

Frictional forces always act in the opposite direction to the object’s motion
Friction occurs when two (or more) surfaces rub against each other
At a molecular level, both surfaces contain imperfections - i.e. they are not perfectly smooth
These imperfections push against each other

Question 15

examples of scalers

Answer 15

distance
speed
mass
energy
temperature

Question 16

force, acceleration and mass equation

Answer 16

force = mass x acceleration

Question 17

weight, mass and gravitational field strength equation

Answer 17

weight = mass x gravitational field strength

Question 18

what is the stopping distance

Answer 18

thinking distance + braking distance

Question 19

what factors affect the vehicles stopping distance

Answer 19

speed
mass of car
condition of cars breaks
road condition
reaction time

Question 20

forces acting on falling objects

Answer 20

Weight
Air resistance

The force of air resistance increases as the object’s speed increases
This is because the object collides with air particles as it moves through the air
The faster the object is travelling, the more collisions it has with the air particles

Question 21

terminal velocity

Answer 21

Terminal velocity is the fastest speed that an object can reach when falling
Terminal velocity is reached when the upward and downward acting forces are balanced
The resultant force on the object reaches zero
The object no longer accelerates and a constant terminal velocity is reached

Question 22

skydiver example of terminal velocity

Answer 22

At the instant the skydiver steps out of the plane, the support force of the plane is no longer acting on the skydiver, but they are not yet falling, so the only force exerted them is the weight force
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force
The skydiver accelerates downward at maximum acceleration

As the skydiver begins to fall, the force of air resistance is very small because the skydiver’s speed is small
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration decreases

As the skydiver accelerates, their speed increases, so the force of air resistance increases
There is a downward acting resultant force on the skydiver
The resultant force is equal to the weight force minus the force of air resistance
The skydiver accelerates downward but the acceleration continues to decrease

As the skydiver’s acceleration decreases, their speed increases at a slower and slower rate
Eventually, the skydiver reaches a speed at which the force of air resistance is equal to the force of weight
The forces are balanced, so the resultant force is zero
The skydiver no longer accelerates and a constant velocity is reached
This is terminal velocity

Question 23

equation with initial speed, final speed, distance moved and acceleration

Answer 23

(final speed)^2 = (initial speed)^2 + (2 x acceleration x distance moved)

Question 24

how to calculate the resultant force that acts along a line

Answer 24

largest force - smallest force

Question 25

Practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands

Answer 25

1. set up a clamp and stand with a G-clamp holding it to the desk so the clamp doesn't fall over 2. strap a ruler to the stand so the 0 is aligned with the bottom of the spring when it is hanging 3. add a 100g mass onto the spring 4. record the mass (kg) and the extension of the spring (cm) 5. repeat 3+4 until all masses have been added 6. remove all masses and repeat whole process 3x and calculate mean for average length of extension extension is the distance the bottom of the spring has moved from where the bottom originally was NEED TO WEAR GOGGLES incase spring snaps don't stand below the weights incase they fall

Question 26

Hooke's Law

Answer 26

The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

Question 27

force - extension graphs

Answer 27

Hooke's law on a graph is only the part where the line is straight and goes through the origin (proportional) when the line is no longer straight then the object does not obey Hooke's law and it has gone beyond its limit of proportionality

Question 28

elastic behavior

Answer 28

the ability of a material to recover its original shape after the force causing the deformation has been removed

Question 29

elastic deformation

Answer 29

where the object does return to its original shape after the force has been removed

Question 30

inelastic deformation

Answer 30

where an object does not return to its original shape after force is removed

Question 31

formula with momentum, mass and velocity

Answer 31

momentum = mass x velocity

Question 32

formula with force, change in momentum and time taken

Answer 32

force = change in momentum / time taken

Question 33

unit for momentum

Answer 33

kg m/s

Question 34

principle of conservation of momentum

Answer 34

the total momentum before an interaction is equal to the total momentum after an interaction if no external forces are acting on the objects the interaction can either be a collision where two objects collide with each other or an explosion where a stationary object explodes into two or more parts

Question 35

how to calculate mass, velocity or momentum of objects

Answer 35

calculate original momentum of each object then add together to get total momentum before as total momentum before = total momentum afterwards calculate momentum of objects after add momentum of objects after together and this number must =momentum before

Question 36

how to explain safety features using momentum

Answer 36

to reduce the force experienced by passengers extend the contract time as force = change in m / time so as change in momentum is constant by changing the time you can change the force. cars have front and back crumple zone to absorb energy and extend the time taken for the impact which then also increases the time taken when the force acts which increases the time taken for the change in momentum to act reducing the force and risk of injury airbags also deploy and are compressible so when you hit them your head compresses them so you are in contact with them for longer so the time taken is longer which decreases the force and deceleration over a longer time seatbelts prevent you hitting the steering wheel and increases the time for you to stop so therefore decreases the force

Question 37

newtons third law

Answer 37

for every force that acts there is an EQUAL sized reaction force of the SAME type, SAME size but OPPOSITE direction each force acts on DIFFERENT objects for example, i am attracted to the earth by weight and the earth is attracted to me by weight

Question 38

formula with moment, force and perpendicular distance from the pivot

Answer 38

moment = force x perpendicular distance so by opening a door far away from its hinge it is much easier as the distance is larger

Question 39

where does the weight of an object act through

Answer 39

its centre of gravity

Question 40

principle of moments

Answer 40

total moments clockwise = total moments anticlockwise in equilibrium

Question 41

unit for moment

Answer 41

Nm newton metre

Question 42

how to calculate force or distance from pivot using principle of moments

Answer 42

calculate the total moments clockwise and also total moments anticlockwise if in equilibrium these will equal each other