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ALevel Physics NEW > Section 4 - Mechanics > Flashcards

Section 4 - Mechanics Flashcards

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1
Q

Define scalar

A

Something with only a magnitude

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2
Q

Define vector

A

Something with a magnitude and a given direction

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3
Q

Give examples of scalars

A

Mass, temperature, time, length, distance, speed, energy

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4
Q

Give examples of vectors

A

Displacement, velocity, force, acceleration, momentum

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5
Q

What are the 2 methods of combining vectors?

A

Scale drawings, Pythagoras and trigonometry

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6
Q

Describe the method of adding vectors together with scale drawings

A

Draw a scale diagram with a ruler and protractor, then measure the missing side with a ruler and find the missing angle with a protractor

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7
Q

Describe the method of adding vectors together with Pythagoras and trigonometry

A

Sketch the vectors end to end, draw a line from the tail of the first vector to the tip of the second vector to give the resultant. Can use Pythagoras to get the magnitude, and trig to get the angle

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8
Q

What does the horizontal component equal when an item is travelling at an angle theta to the horizontal?

A

V cos theta

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9
Q

What does the vertical component equal when an item is travelling at an angle theta to the horizontal?

A

V sin theta

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10
Q

What do free body force diagrams show?

A

All forces on a single body

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11
Q

What should a free body force diagram show?

A

All forces that act on a body, but not the force that it exerts on the rest of the world

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12
Q

What is a moment?

A

A turning effect of a force

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13
Q

What happens when moments aren’t balanced?

A

The object will turn

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14
Q

Define a moment

A

force times the perpendicular distance from the point to the line of action of the force

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15
Q

State the principle of moments

A

For a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of anti clockwise moments about the same point

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16
Q

What forces act in a lever?

A

An effort force acts against a load force by means of a rigid object rotating around a pivot

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17
Q

What is a couple?

A

A pair of coplanar forces

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18
Q

What are coplanar forces?

A

Forces of equal magnitude but in opposite directions

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19
Q

What does a couple produce?

A

No resultant linear force, but does produce a turning effect

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20
Q

Define the moment of a couple?

A

The size of one of the forces times the perpendicular distance between the lines of action of the forces

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21
Q

Define mass

A

The amount of matter in it

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22
Q

What does a greater mass lead to in terms of motion?

A

The greater resistance to a change in velocity

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23
Q

What happens to the mass when the gravitational field changes?

A

It doesn’t change

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24
Q

What is weight?

A

A force experienced by a mass due to a gravitational field

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25
Q

The happens to the weight when the gravitational field changes?

A

It varies

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26
Q

What is the centre of mass?

A

A point where the mass is thought to be most concentrated

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27
Q

What are the 2 methods of finding the centre of mass?

A

Symmetry or experiment

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28
Q

How can you find the centre of mass by symmetry?

A

It is at its centre, and halfway through the thickness

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29
Q

How can you find the centre of mass by experiment?

A
  • Hang the object freely from a point and draw a vertical line downwards from the point of suspension
  • Hang the object from a different point and repeat the process
  • The COM is where the lines cross
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30
Q

What does the stability of an object depend on?

A

COM and base area

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31
Q

When will an object topple over?

A

When the line of action of its weight falls outside its base area

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32
Q

What conditions make an object more stable?

A

Wider base and low centre of mass

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33
Q

Define speed

A

How fast something is moving

34
Q

Define displacement

A

How far an object’s travelled from its starting point in a given direction

35
Q

Define velocity

A

The rate of change of an object’s displacement

36
Q

Define acceleration

A

The rate of change of an object’s velocity

37
Q

What does acceleration look like on a displacement-time graph?

A

A curved line

38
Q

What does faster acceleration look like on a displacement-time graph?

A

A steeper gradient

39
Q

What does slower acceleration look like on a displacement-time graph?

A

A shallower gradient

40
Q

What does deceleration look like on a distance-time graph?

A

A decreasing gradient

41
Q

What does the gradient of a displacement-time graph tell you?

A

Velocity

42
Q

How can you find the velocity on a curved displacement graph?

A

Draw a tangent and find the gradient of a tangent

43
Q

What does the gradient of a velocity-time graph tell you?

A

Acceleration

44
Q

What does the area under a velocity-time graph tell you?

A

Displacement

45
Q

What does the area under an acceleration-time graph tell you?

A

Change in velocity

46
Q

What are the advantages of data loggers?

A
  • More accurate
  • Much higher sampling rate than humans
  • Can see data in real time
47
Q

What is free fall?

A

When there is gravity acting on an object and nothing else

48
Q

What affects the vertical component motion?

A

Gravity

49
Q

Is the horizontal component motion affected by gravity?

A

No, it just moves at a constant speed

50
Q

How would you solve a problem if a projectile is launched at an angle?

A
  • Resolve initial velocity into horizontal and vertical components
  • Use vertical component to work how long it is in the air/how high it goes
  • Use horizontal component to work out how far it goes horizontally
51
Q

Describe how you would use the horizontal component to work out time when a projectile is launched at an angle

A
  • Halfway through the ball’s flight the v=0

- use v = u + at, and multiply by 2

52
Q

State Newton’s 1st law

A

The velocity of an object will now change unless acted upon by a resultant force

53
Q

State Newton’s 2nd law

A

Force equals mass times acceleration

54
Q

Who proved that all objects fall at the same rate?

A

Galileo

55
Q

State Newton’s 2rd law

A

Each force has an equal and opposite reaction force

56
Q

What is friction?

A

A force that opposes motion

57
Q

What are the 2 main types of friction?

A

Dry friction between solid surfaces

Fluid friction

58
Q

What is a fluid?

A

Something that can flow - air or a gas

59
Q

In fluid friction, what does the force depend on?

A

The viscosity of the fluid

60
Q

What is fluid friction also known as?

A

Drag

61
Q

What does the magnitude of fluid friction depend on?

A

The speed and the shape

62
Q

What are the main 3 facts about fluid friction?

A
  • Act in the opposite direction to the motion
  • Can never speed things up/start things moving
  • Convert KE into heat and sound
63
Q

Which direction does lift act in?

A

Perpendicular to fluid flow

64
Q

What occurs at terminal velocity in a car?

A

Driving force equals friction force

65
Q

Describe the 3 stages of driving from rest up to terminal velocity

A
  • Car accelerates from rest, with resultant and driving force forward
  • As speed increases, friction increases which reduces resultant force on car and reduces acceleration
  • Car reaches speed where frictional force equals driving force -> No resultant force
66
Q

Describe the velocity time graph for a parachute

A

The skydiver accelerates up to its terminal velocity, and then the parachute opens and there is a sharp decrease in velocity and then there is a terminal velocity after the parachute has opened

67
Q

When is momentum conserved?

A

When no external forces act on the system

68
Q

What is an elastic collision?

A

When momentum and KE are conserved

69
Q

What is an inelastic collision?

A

Some of KE is converted into other forms of energy, but momentum is conserved

70
Q

What is an impulse?

A

Change in momentum

71
Q

How can you calculate impulse from a force-time graph?

A

The area under it

72
Q

What does reducing the impact time of a collision do to the force?

A

Increases the force

73
Q

State some vehicle safety features

A

Crumple zones - The front and back of the car can crumple, making the car take longer to stop
Seat belts - Stretch slightly, increasing time taken for wearer to stop and spread force around body
Air bags - Slow down passengers more gradually, and preventing them from hitting hard surfaces in the car

74
Q

When is work done?

A

When energy is transferred

75
Q

Why do you normally need a force to move something?

A

As you have to overcome another force

76
Q

What is work?

A

The energy that’s been changed from one form to another

77
Q

Is the force always in the same direction as the movement?

A

No

78
Q

What does the area under a force-displacement graph represent?

A

Work done

79
Q

What is power?

A

Energy transferred per second

80
Q

State the principal of energy

A

Energy cannot be created or destroyed. It can be transferred from one form to another but the total amount of energy in a closed system will not change

81
Q

What is kinetic energy?

A

The energy of anything moving

82
Q

What is gravitational potential energy?

A

The energy you gain of you lift something up

ALevel Physics NEW (12 decks)

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