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Physics 21st Century > Explaining motion > Flashcards

Explaining motion Flashcards

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1
Q

What does the speed of an object tell us?

A

How far it will travel in a certain time

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2
Q

How do you calculate speed?

A

Speed (m/s) = distance travelled (m)/time(s)

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3
Q

If the object is not travelling at a constant speed what does distance/time give us?

A

The average speed.

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4
Q

How many seconds in a minute?

A

60

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5
Q

How many seconds in an hour?

A

3600

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6
Q

If the question gives time in hours, and you need to calculate speed in m/s, what can you do?

A

Convert hours into seconds.

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7
Q

What does average speed over a very short time interval give you?

A

A value that is close to instantaneous speed (though it will still be an average over that small time interval)

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8
Q

What is the displacement of an object?

A

The distance from the start - so earth travels a long way in a year, but the displacement (seen from the sun) is zero.

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9
Q

Why is displacement a vector?

A

It has size (magnitude) and direction.

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10
Q

What is velocity?

A

Speed in a certain direction.

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11
Q

Why is velocity a vector?

A

It has magnitude and direction.

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12
Q

When plotting a distance time graph, where does time go?

A

On the X axis

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13
Q

When plotting a distance time graph, where does distance go?

A

On the Y axis.

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14
Q

What does a horizontal line on a distance time graph tell you?

A

The object being tracked is not moving.

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15
Q

What is horizontal?

A

Parallel to the floor … the X axis on a graph

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16
Q

What is vertical?

A

Sticking straight up into the air… the Y axis on a graph.

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17
Q

On a distance time graph, what is the gradient equal to?

A

The speed, but only if you have time on the X axis.

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18
Q

On a distance time graph, what does a curved line show?

A

The speed is changing

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19
Q

On a distance time graph what does a steeper line mean?

A

The object being tracked is moving faster.

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20
Q

On a distance time graph what would a vertical line mean?

A

The object has moved an infinite amount of distance in zero time.

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21
Q

What is a displacement time graph?

A

A way of showing a return journey, where displacement goes to 0 when the object returns.

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22
Q

What does the graph going below the X axis mean on a displacement time graph?

A

The object went past the starting point and kept going, it is now behind the position that it started at.

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23
Q

What is acceleration?

A

The rate at which an object changes velocity

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24
Q

If an object is slowing down, what is it doing?

A

Showing negative acceleration. Can be called retardation or deceleration.

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25
Q

What is the unit of acceleration?

A

metres per second per second - m/s^2

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26
Q

What is a car doing when going round the corner at a constant speed?

A

Accelerating. It is changing direction, this is still acceleration

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27
Q

On a speed-time graph, what goes on the X axis?

A

Time

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28
Q

On a speed-time graph, what goes on the Y axis?

A

Speed

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29
Q

On a speed time graph, what does a horizontal line mean?

A

The object is going at constant speed.

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30
Q

On a speed time graph, what does it mean if the graph is on the X axis?

A

The object is not moving (stationary)

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31
Q

What does the gradient of the graph tell you?

A

The acceleration of the object (only if time is on the X axis!)

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32
Q

What does a velocity-time graph show?

A

It takes direction of the object into account - however, it does so only in one direction. If you want to have more fun you need a 3D graph… and at least A level maths :D

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33
Q

If a velocity-time graph goes under the X axis, what does that show?

A

The object is moving in the opposite direction to the one it started in.

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34
Q

What is a force?

A

A push or a pull between two objects.

35
Q

How many forces at the time?

A

They always act in pairs.

36
Q

What is a repulsive force?

A

One that pushes objects apart

37
Q

What is an attractive force?

A

One that pulls objects together

38
Q

What is the size of each force in the pair?

A

Equal and opposite.

39
Q

Why are forces vectors?

A

They have magnitude and direction.

40
Q

What is friction?

A

A force that opposes the movement when two surfaces slide over one another.

41
Q

What does the size of the friction force depend on?

A

Roughness of the surface; how hard the surfaces are pushed together.

42
Q

What happens when you try to move something?

A

Friction will equal the applied force and the object remains at rest. If you push harder friction pushes back harder too, until eventually you are pushing hard enough to overcome the force and the object will start to move.

43
Q

What happens to the kinetic energy of two surfaces in contacts?

A

It is transferred to heat energy (rub your hands together).

44
Q

How can you reduce friction in a machine?

A

Lubrication (oil) is used.

45
Q

When there are multiple forces acting on an object how can you work out the resultant force?

A

You can calculate it by adding/subtracting the forces - remember to take the direction into consideration.

46
Q

What happens when forces are unbalanced?

A

The object will accelerate.

47
Q

What is weight?

A

The force on an object due to gravity.

48
Q

What is mass?

A

The amount of matter in an object.

49
Q

What is weight measured in?

A

Newtons.

50
Q

What is mass measured in?

A

Kg

51
Q

What happens to my weight and mass if I go to the moon?

A

My weight goes down, my mass remains the same.

52
Q

What is acceleration due to gravity on earth?

A

9.8 m/s^2

53
Q

Where does the force of gravity act towards (on earth)?

A

The centre of the earth.

54
Q

What slows down falling objects (on earth)?

A

Air resistance, or drag.

55
Q

Which direction does drag act in?

A

The opposite direction to the movement of the object

56
Q

What happens to drag as the speed of the object increases?

A

It increases

57
Q

What happens to drag as the surface area of the object increases?

A

It increases

58
Q

What is the constant maximum speed of a falling object known as?

A

Terminal velocity

59
Q

How does drag act on a car?

A

It opposes the direction of travel

60
Q

What is momentum?

A

Mass in motion - calculated by mass x velocity

61
Q

How would you calculate the change of momentum of an object?

A

Change of momentum (kg m/s) = resultant force(N) x time (s)

62
Q

What is the force exerted by change of momentum?

A

Force (N) = change of momentum (kg/s) /time (s)

63
Q

Why do we use air bags and crumple zones in cars?

A

They increase the impact time - if you double the impact time you halve the force as the force = change in momentum /time. You must mention momentum if you get this question.

64
Q

What is work?

A

The energy used by the movement of a force.

65
Q

What are energy and work measured in?

A

Joules.

66
Q

What is energy?

A

The ability to do work.

67
Q

How would you calculate work done?

A

work done (J) = Force (N) x distance moved (in the direction of the force!) (m)

68
Q

When you do work on an object, what happens?

A

Energy is transferred to the object.

69
Q

What happens when an object does work?

A

The object transfers energy to another object.

70
Q

How do you calculate how much energy has been transferred by the work done?

A

Amount of energy transferred (J) = Work done (J)

71
Q

What forms of energy can work?

A

They all can.

72
Q

Is all the energy that you have transferred as work done?

A

No, some is not transferred to the object and is lost as heat.

73
Q

What are you working against when you lift an object?

A

Gravity

74
Q

How much work can 1 Joule do?

A

It can lift a weight of 1 Newton a distance of 1 metre.

75
Q

Where does the energy expended lifting something go?

A

It is transferred to gravitational potential energy (GPE) of the object.

76
Q

How would you calculate the change in GPE (gravitational potential energy)?

A

Change in GPE (J) = weight (N) x vertical height difference.

77
Q

What is the energy an object has due to the fact it is moving?

A

Kinetic energy

78
Q

How do you calculate kinetic energy?

A

Kinetic energy (J) = 1/2 x mass (kg) x velocity^2 (VELOCITY IS SQUARED FIRST)

79
Q

What does the work done by an applied force on an object equal?

A

Work done = force x distance moved

80
Q

What is meant by conservation of Energy?

A

Energy can be neither created nor destroyed.

81
Q

What are the energy transfers as a roller coaster goes round the track (assume no friction or drag)

A

Gravitational potential energy converts to kinetic energy, and back again.

82
Q

What really happens to the energy of a roller coaster?

A

Some is lost as heat due to friction and drag.

83
Q

What is the mathematical relationship between GPE and kinetic energy?

A

loss of GPE = gain in kinetic energy (pretending there is no friction/drag)

Physics 21st Century (8 decks)

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