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A-Level Physics > [AS] Forces and Energy > Flashcards

[AS] Forces and Energy Flashcards

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1
Q

What is Newton’s First Law?

A

The velocity of an object will not change unless a resultant force acts on it

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2
Q

What is Newton’s Second Law?

A

Acceleration is proportional to resultant force

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3
Q

What is Newton’s Third Law?

A

Every force has an equal and opposite reaction force

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4
Q

What kind of friction acts between solid surfaces?

A

dry friction / contact friction

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5
Q

What kind of friction acts between fluid surfaces?

A

drag / fluid resistance / air resistance

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6
Q

What do you call a force that opposes motion?

A

Friction

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7
Q

What does friction convert kinetic energy into?

A

Heat and Sound

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8
Q

What is lift?

A

An upwards force on an object moving through a fluid.

It acts perpendicular to the direction of the fluid’s flow

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9
Q

What force acts perpendicular to the direction a fluid flows in?

A

Lift

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10
Q

What causes lift?

A

Fluid flowing changes direction as it moves over object’s shape

Difference in pressure on either side of the object

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11
Q

What two forces are equal at terminal velocity?

A

Friction and Driving Force

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12
Q

What are the two conditions for an object reach terminal velocity?

A
  1. a constant Driving Force

2. a Frictional Force that increases with speed

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13
Q

How can you increase a vehicle’s maximum speed?

A
  1. increase the Driving Force (increase engine size)

2. reduce the Frictional Force (more streamlined body)

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14
Q

Describe how a skydiver reaches terminal velocity

A
  1. Skydiver initially accelerates due to gravity
  2. Air resistance increases until it equals his weight (terminal velocity)
  3. The parachute opens, increasing air resistance
  4. He decelerates until he is slow enough for air resistance to equal weight
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15
Q

What does ‘resolving a force’ mean?

A

Splitting it into perpendicular components

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16
Q

What is always true for three coplanar forces acting on a point in equilibrium?

A

The three forces can be drawn as a closed triangle

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17
Q

For a force triangle, what is true about the direction of the forces?

A

You can trace their directions around the triangle in a loop

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18
Q

How do you find the resultant force of two component forces?

A

Add them together

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19
Q

What is density?

A

Mass per unit volume

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20
Q

What is an object’s density dependent on?

A

The material it is made of

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21
Q

Under what condition will a solid object float in a fluid?

A

If its density is lower than the fluid’s

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22
Q

What is pressure?

A

Force per unit area

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23
Q

What is pressure measured in?

A

pascals (Pa)

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24
Q

What is one pascal equivalent to?

A

Nm^-2

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25
Q

What are the SI base units of the Newton?

A

kg⋅m⋅s^-2

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26
Q

What is the extra pressure on an object in a depth in a fluid equal to?

A

p = hρg

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27
Q

What is upthrust?

A

An upward force a fluid exerts on objects that are fully or partially submerged in the fluid

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28
Q

What is Archimedes’ Principle?

A

Upthrust is equal to the weight of the displaced fluid

29
Q

Does the mass of an object change when g changes?

A

No

30
Q

Does the weight of an object change when g changes?

A

Yes

31
Q

What is weight a measure of?

A

Force

32
Q

What is weight equal to?

A

mg

33
Q

Where should you assume all of the mass of an object acts?

A

Centre of mass

34
Q

When will an object topple over?

A

If the centre of mass is outside its base

35
Q

What is a moment?

A

The turning effect of a force

36
Q

How do you calculate the moment?

A

Force × perpendicular distance from picot

37
Q

What happens if the moments are imbalanced?

A

The object will turn

38
Q

What is the principle of moments?

A

Sum of clockwise moments

sum of anticlockwise moments

39
Q

What is a couple?

A

Two equal-size coplanar forces acting parallel to each-other in opposite directions

40
Q

How do you calculate the moment of a couple?

A

Size of one of the forces × distance between them

41
Q

How do you calculate momentum?

A

Mass × velocity

42
Q

Is momentum conserved?

A

Yes

43
Q

What is an elastic collision?

A

Momentum and kinetic energy are conserved

44
Q

What is an inelastic collision?

A

Momentum is conserved

Some kinetic energy is converted to other forms (e.g. sound)

45
Q

What is impulse?

A

The change in momentum

46
Q

How do you calculate impulse from a graph?

A

Area under a force-time graph

47
Q

What is the area under a force-time graph?

A

Impulse

48
Q

What is a Crumple zone?

A

An area at the front/rear of a car designed to crumple on impact

49
Q

How does a Crumple zone reduce risk?

A

Absorb some of the car’s kinetic energy

Increase time taken to slow down, reducing force

50
Q

When is work done?

A

When energy is transferred?

51
Q

What is done when energy is transferred?

A

Work

52
Q

What happens to kinetic energy when an object stops moving?

A

It is transferred to another form of energy

53
Q

Why do you need a force to move an object?

A

To overcome another force

54
Q

Define work done

A

The amount of energy transferred from one form to another when a force causes movement

55
Q

What is an equation for work done with force and distance?

A

Work done = Force × distance

56
Q

How do you calculate work done from a graph?

A

Area under a force-displacement graph

57
Q

What is the area under a force-displacement graph?

A

Work done

58
Q

Define power

A

The rate that work is done

Energy transferred per second

59
Q

What is the unit of Power?

A

Watt

60
Q

What is kinetic energy?

A

Energy an object has due to movement

61
Q

What is gravitational potential energy?

A

Energy an object has due to its position in a gravitational field

62
Q

How is GPE related to Work?

A

GPE gained =

work done moving through a height

63
Q

What is change in kinetic energy of an object equal to?

A

Work done on the object

64
Q

What it the Principle of Conservation of Energy?

A

Energy can’t be created or destroyed. It can only be transferred between forms

65
Q

What is lost energy?

A

Energy transferred to a waste form

66
Q

Is it possible for no energy to be lost?

A

No

67
Q

What causes heat loss?

A

Friction

68
Q

What is efficiency?

A

The ratio of useful energy output to total energy input

A-Level Physics (13 decks)

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