P2 Flashcards
(91 cards)
1
Q
How do you measure distance and time in the laboratory?
Trolley moving down a ramp:
A
Distance:
Use a ruler
Time:
Use a stopwatch or light gates
2
Q
How do you measure distance and time in the laboratory?
Falling object:
A
Distance:
Use a ruler
Time:
Use light gates
3
Q
How do you calculate average speed?
A
Average speed =distance/time
4
Q
Is force a vector or scalar and how do you present it?
A
Some quantities such as force have a magnitude (size and a direction)
Force is a vector.
-the length of the arrow shows the magnitude and the direction of the arrow shows the direction.
5
Q
What the difference between a vector and scalar?
A
Vectors have direction and magnitude where as scalars only have magnitude
Magnitude = size
Force is a vector, something like time or distance is a scalar.
6
Q
What is the difference between displacement and distance?
A
Distance is your total amount of travel where as displacement is the direction and amount away from your starting point.
7
Q
What is the difference between speed and velocity?
A
-Speed is a scalar quantity e.g 15 m/s
-Velocity is a vector quantity. It has a direction as well as magnitude so 15 m/s south is a velocity
8
Q
How do you add vector quantities?
A
20m/s 20m/s 40m/s
—> + —> = —>
20m/s 20m/s 0m/s
—> + <— = zero
9
Q
What is acceleration?
A
The change in velocity per second
10
Q
What does uniform acceleration mean?
A
Uniform acceleration means that the acceleration does not change.
11
Q
What does + mean in velocity
A
Speeding up
12
Q
What does - mean in velocity
A
Slowing down
13
Q
What is the formula for acceleration?
A
Acceleration (m/s^2) = change in velocity (m/s) / time (s)
14
Q
How do you calculate acceleration if you know the final and initial velocity?
A
Acceleration(m/s^2) = final velocity-initial velocity (m/s) / time(s)
15
Q
What does a graph of distance against time mean?
A
A graph of distance against time tells you about the speed of an object on its journey. The speed is equal to the gradient (or slope) of the graph.
-a straight line means the objects speed is constant because the gradient does not change
-a horizontal line means the object is not moving
-the steeper the line, the faster the object is travelling.
16
Q
How is a distance-time graph different from a displacement-time graph?
A
-A distance time graph shows the total distance travelled
-if you plot a displacement time graph then the gradient can be positive, zero or negative. The gradient of the graph is the velocity so it has direction as well as a magnitude.
17
Q
How do you calculate speed from a graph?
A
Draw a right angles triangle under the line
Change in distance/change in time
18
Q
How do you calculate velocity from a graph?
A
Velocity= final displacement- initial displacement/ change in time
19
Q
What does it mean if the acceleration is negative?
A
The object is slowing down
20
Q
What does it mean if the acceleration is positive?
A
The object is speeding up
21
Q
How do you calculate distance travelled?
A
The distance travelled is the area Under a speed time graph. The displacement is the area under a velocity time graph.
(The area under a graph =distance/ displacement)
22
Q
What is an equation of motion?
A
There are equations that link velocities, acceleration, distance and time for objects that have constant acceleration. You need to be able to apply this equation of motion to calculate a final velocity, initial velocity , acceleration or displacement.
(Final velocity (m/s))^2 - (initial velocity (m/s))^2 = 2 x acceleration (m/s^2) x distance (m)
23
Q
How do you calculate kinetic energy?
A
Kinetic energy(J) = 0.5 x mass(kg) x (speed(m/s))^2
24
Q
What is very important in physics?
A
REARRANGING
25
How do forces arise?
Pairs of forces arise when objects interact:
In an interaction pair:
-Each force acts on a different object
-the forces are the same size, and type (e.g. gravitational)
-the forces act in opposite directions
26
What is Newton’s third law?
For every action there is an equal and opposite reaction
27
What are non-contact forces?
Some objects interact without being in contact with each other. You have learned about these non-contact forces:
Electrostatics
Magnetism
Gravity
-these forces arise because charges,magnets, and masses interact at a distance. Electric charges and magnets both repel and attract, but gravity only attracts. These forces are the result of fields. A field is a region where an electrical charge, a magnetic material or mass experiences a force. forces are vectors so you represent a force with a force arrow. You usually draw force arrows for non-contact forces from the centre of the object.
28
What are contact forces?
When you stand on a diving board, the board pushes up on you. Solid surfaces can exert a force on objects that exert a force on them. You draw contact force arrows from the point of contact.
-the bonds between the atoms behave like springs.
29
About the contact force-friction on a sliding box
The interaction pair:
-The force of the box on the surface
-The force of the surface on the box
The mechanism that produces it:
The atoms that make up the surfaces interact when tough surfaces slide over each other
30
About the contact force-drag on a falling leaf(drag is air resistance it water resistance)
The interaction pair:
-The force of the falling leaf in the air
-the force of the air on the leaf
31
About the contact force-normal contact force acting on an elephant
The interaction pair:
-the force of the elephant on the ground
-the force of the ground on the elephant
The mechanism that produces it:
Solid objects deform slightly when you exert a force on them. The bonds between the particles are compressed.
32
About the contact force-upthrust in a floating boat
Interaction pair:
The force of the boat on the water
The force of the water on the boat
The mechanism that produces it:
Gravity produces pressure differences in a fluid. The pressure produces a net upwards force.
33
About the contact force- tension in the cord of a bungee jumper
The interaction pair:
-the force of the bungee jumper on the bungee cord
-the force of the bungee cord on the bungee jumper
The mechanism that produces it:
Solid objects deform slightly when you exert a force on them. The bonds between the particles are stretched.
34
What is weight?
Weight is shorthand for the gravitational force of one object on another.
35
How do you draw a free body diagram?
You know that the force or forces acting on an object can be from several different interaction pairs
Step 1: identify all the non-contact pairs
Step 2: identify all the contact pairs
Step 3: focus on a single object. Draw the object with arrows showing all the forces acting in the object
“The force of x on y” “the force of y on x”
36
How do you find the resultant force?
Forces are vectors so you need to account for their direction when you add them.
5N<————0——>3N
Resultant force = <——0 2N
37
How do you find resultant forces at an angle?
You use Pythagoras c^2=a^2+b^2
38
What is Newton’s first law?
“An object will continue to stay at rest with uniform velocity unless a force acts on it”
It takes a resultant force to change the motion (speed or direction) of an object
39
Why do objects continue to move at a steady speed?
If the speed or direction of an object does not change then the resultant force is zero. A steady speed means that that there is a zero resultant force.
The toolkit lost by an astronaut will continue to move with a steady velocity if no force acts on it.
40
What happens if there is no friction?
If there is no friction, you do not need to exert a force for something to continue at a uniform velocity
41
What is equilibrium?
When the resultant force is zero so the motion does not change. The objects are in equilibrium.
42
What happens when the resultant force isn’t zero?
A resultant force can:
-Change the speed of an object
-change the direction of motion on an object
-change both the speed and direction of motion of an object
43
What is Newton’s second law and how do you calculate with it?
Newton’s second law states that the acceleration that the resultant force produces on an object depends on:
-The size of the resultant force
-the mass(inertia) of the object
Force(N) = mass(kg) x acceleration(m/s^2)
44
What is the calculation for force?
Force(N) = mass(kg) x acceleration(m/s^2)
45
Why would objects move in a circle?
An object moving in a circle at a constant speed is still accelerating even though it’s speed does not change.
-It is constantly changing direction, so it’s velocity is constantly changing.
-To do this a force directed towards the centre of the circle acts on the object
46
How do you explain the motion of objects when the forces are at an angle?
-you can analyse these situations by resolving the forces so that you are only dealing with forces that act in two directions at right angles
-use a scale diagram
47
How do you explain the motion of falling objects?
When you jump out of a plane:
-you accelerate
-your motion changes due to a resultant force acting on you
-the air exerts a force on you but the Earth exerts a larger force on you
As you accelerate the force of the air increases.
-eventually the force of the air equals the force of the earth on you, and your motion no longer changes.
-you have reached terminal velocity
48
How do you explain the motion of rockets?
-When a rocket takes off there is a resultant force on it that produces a large acceleration.
-the burning fuel pushes exhaust gases out of the bottom of the rocket. The gases pushing on the rocket and the rocket pushing on the gases are another example of newtons third law
-when the force of the gases on the rocket is bigger than the force of the earth on the rocket then the rocket will accelerate
49
What is momentum?
Momentum is a vector so when you do calculations involving momentum you need to take into account direction.
50
How do you calculate momentum?
Momentum(kgm/s) = mass (kg) x velocity (m/s)
51
What is the conservation of momentum?
In any collision momentum is conserved, so the momentum before is equal to the momentum afterwards. This is the law of conservation of momentum.
52
What happens when objects collide?
-In an elastic collision no energy is transferred to other stores.
-the energy in the kinetic store stays the same
-eg a ball hits another ball, the initial ball will stop but the momentum of the initial ball will cause the new ball to move
53
What happens when objects collide and join together?
-In an elastic collision some energy is transferred to other stores. One example is when snooker balls collide, and energy is transferred by sound to a thermal store.
-another example is a collision after which the velocity of the combined object is less than that of the original objects.
54
What is Work?
-Doing work in science is about using forces to transfer energy between stores.
-You use a force to lift your suitcase into a car, and you do work against gravity.
-You have shifted energy to a gravitational store
-when you pull your suitcase along you are doing work against friction. Energy is shifted to a thermal store.
55
What is the equation for work?
Work done(J) = force(N) x distance (m)
56
Why are joules equal to newton -metres?
You know that a newton is a derived unit and 1N = 1kgm/s^2
If you multiply force and distance the unit of the quantity you calculate is the newton metre
1Nm= 1kgm/s^2 x m = 1kgm^2/s^2
This is the same unit as the unit of kinetic energy. One newton metre is the same as 1 joule
57
What is a newton
A newton is a derived unit and 1N = 1kgm/s^2
58
What is power?
-you have learned that power tells you the rate at which energy is transferred a powerful person can run upstairs in a short time.
-If both people are the same weight when they do the same amount of work.
-Each person transfers the same amount of work.
-Each person transfers the same amount of energy to a gravity store.
-The more powerful person transfers the energy in a shorter time.
59
How do you calculate power?
Power(w) = work done(J) / time (s)
60
How do you change the shape of an object?
Forces can compress, stretch or bend objects. You need more than one force to do this.
61
What is a “plastic” object?
Materials that stretch but do not return to their original shape, such as modelling clay. They are deformed or distorted when you apply forces and stay that way when you remove the forces.
62
What is an “elastic” object
An object that does return to its original shape when you remove forces on it.
63
What happens when you stretch a spring?
-Force and extension have a linear relationship up to a point.
-This is called the limit of proportionality.
-There is an elastic limit, if you go beyond this elastic limit the spring/ object shall not return to its original length-it is permanently deformed.
64
How do you calculate the spring constant?
-If you double the force on a spring, it’s extension doubles.
-The extension of a spring is promotional to the force acting on it until you reach limit of proportionality.
-This is Hooke’s law.
65
What is the calculation for hooke’s law?
Force exerted by a spring(N) = spring constant (n/M) x extension (m)
-The gradient of the linear section of a graph of force against extension is the spring constant.
-The constant shows you how stiff/ difficult it is to stretch
66
How do you calculate the energy transferred in stretching a spring?
Energy transferred in stretching (J) =
0.5 x spring constant(N/m) x (extension (m))^2
Energy transferred is also “work done”
67
What happens when you stretch other materials?
-The graph for an elastic band shows that there is a non-linear relationship between force and extension
-you cannot use an elastic band in a newtonmeter.
-You need a spring as it obeys hooke’s law
68
How can you describe the graph of a bungee chord?
-When you blow up a rubber balloon, at first it is difficult.
-The rubber is quite stiff.
-Once you’ve started blowing it up, it requires less force to produce an extension.
-Finally it becomes stiffer again
69
What is a gravitational field?
-A gravitational field is a region where a mass experienced an attractive force.
-All matter has a gravitational field that causes attraction
70
How do you calculate the gravity force?
Gravity force (N) = mass (kg) x gravitational field strength (N/kg)
71
What is gravitational field strength?
Gravitational field strength,g, or gravity constant,g, is a measure of the force in a 1kg mass when it is in a gravitational field due to another mass.
-Mass does not change, but the force on the mass depends on the field.
-A gravitational field is a region where a mass experiences an attractive force
-The same size force acts on each object. The force is bigger if:
-the mass of one or both of them is bigger
-the distance between them is smaller
72
What is weight?
-Weight is what we call the force of the Earth on an object, such as you, when it is on the Earths surface.
-You measure weight using scales, or with a newton meter.
73
What is the acceleration due to gravity?
-The symbol, g, is also used for the acceleration due to gravity.
Gravity force (N) = mass (kg) x gravitational field strength (N/kg)
Resultant force (N) = mass (kg) x acceleration due to gravity (m/s^2)
Acceleration due to gravity,g (also called acceleration of free fall), is 10m/s^2 on the earth
74
What is gravitational potential energy?
-when you lift an object in a gravitational field strength you transfer energy to a gravity store.
-this energy is called gravitational potential energy
75
How do you calculate gravitational potential energy?
Gravitational potential energy (J) = mass (kg) x height (m) x gravitational field strength (N/kg)
76
How do forces cause rotation?
-the legs of your chair act as a pivot.
-the force acting on you when you lean back acts at a certain distance from the pivot, so your chair turns.
-this is called the effect, of moment
-it is more difficult to produce a turning effect when the force acts closer to the pivot.
-For example without a spanner to a nut, it would be very difficult to turn
77
How do you calculate the moment of a force?
Moment of a force (Nm) = force (N) x distance (m)
78
What is the principle of moments?
An object is balanced if the anti-clockwise moments are equal to the clockwise moments about the pivot.
-This is the principle of moments.
79
How do levers transmit forces?
-A lever is a force multiplier.
-It transmits forces by rotating about a pivot.
80
What is the effort in a lever?
The effort is the force that you exert on the lever.
81
What is the load in a lever?
The load is the force that the lever exerts on the load.
82
What is the mechanical advantage?
Mechanical advantage = load/effort
83
How do you calculate effort?
Effort = (load x distance from pivot to load) / distance from pivot to effort
84
How do gears transmit forces?
-gears are like levers that rotate
-a small cog can rotate at a certain force that makes a bigger force rotate. The bigger force will exert a bigger force but will not move as far.
85
What are other types of force multipliers?
Ramps,pulleys,wheels,gears and levers
86
How does the pressure in a fluid cause a force?
-when you are underwater you feel water pressure acting on all sides of your body, not just from above.
87
How do you use the equation for pressure?
-there is a bigger force if the pressure is bigger or the area is bigger
Pressure(Pa) = force normal to the surface (N) / area of that surface (m^2)
88
What is a hydraulic machine?
-A machine that uses a liquid to transmit forces is called a hydraulic machine.
-A simple hydraulic machine is made of two pistons connected by a pipe.
-when you push on one piston the pressure is transmitted through the liquid, and the other piston moves.
89
How do you calculate charge
Charge = current x time
90
How much is one charge
1.6 x10^-19 coulombs
91
How do you calculate the number of electrons needed to transfer a charge
Q / Q1
