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Physics paper 2 > Forces > Flashcards

Forces Flashcards

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1
Q

What is a vector quantity?

A

A quantity that has a size and a direction e.g. force, velocity

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2
Q

What is a scalar quantity?

A

Quantities with size but no direction e.g. speed, distance

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3
Q

What is a contact force?

A

When two objects have to be touching for a force to act e.g. friction

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4
Q

What is a non contact force?

A

Where objects do not need to be touching for the force to act e.g. magnetic forces

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5
Q

How does gravity effect anything near a planet or star?

A

On the surface of the planet, it makes all things accelerate towards the ground it gives everything a weight

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6
Q

What is weight?

A

The force acting on an object due to gravity

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7
Q

What is a centre of mass?

A

Where the force is acting at a single point on the object; normally the centre

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8
Q

How do you find the weight of an object?

A

Mass x gravitational field strength

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9
Q

How is a free body diagram used?

A

The size of the arrows shows the relative magnitude of the forces and the direction show the direction of the force acting on the object

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10
Q

What is resultant force?

A

If there are more than one forces acting on an object (with the same effect) the overall effect on the object is called resultant force

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11
Q

What happens when a force moves an object?

A

Energy is transferred and work is done on the object

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12
Q

How can an object be elastically deformed?

A

If it can go back to its original shape and length when the force is removed

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13
Q

How can an object be inelastically deformed?

A

If it doesn’t return to the original shape and length after the force has been removed

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14
Q

How does an elastically deformed object affect the energy transferred?

A

When work is done on the object, energy is transferred to the elastic potential energy stored. If the object is elastically deformed, ALL of the energy goes to the elastic potential energy store

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15
Q

What is the relationship between extension and force?

A

They are directly proportional

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16
Q

Why does force and extension being directly proportional stop?

A

There is a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally; this is known as the limit of proportionality

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17
Q

What is pressure?

A

The force per unit area

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18
Q

What is density?

A

A measure of compactness of a substance

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19
Q

What happens when the depth of a liquid increases?

A

The number of particles above that point increases which means that the weight of these particles adds to the pressure felt at that point

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20
Q

What happens when an object is submerged in a fluid?

A

The pressure of the fluid exerts a force on it from every direction

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21
Q

What is the upthrust of an object submerged in water?

A

This is a resultant force upwards and is equal to the weight of the object submerged

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22
Q

What happens if an object floats?

A

This means that the weight of the object is the same as the upthrust

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23
Q

What does an object float upon depend on?

A

The density

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24
Q

What happens to an object that is less dense than the fluid it is placed in?

A

This means that it weighs less than the equivalent volume of fluid so it displaces a volume of fluid that is equal to its weight before it is completely submerged

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25
Q

What happens to an object that is denser than the fluid it is placed in?

A

It is unable to displace enough fluid to equal its weight, so its weight is always larger than the upthrust and it will sink

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26
Q

Why does atmospheric pressure decrease with height?

A

Atmospheric pressure is created on a surface by molecules colliding with that surface, so when altitude increases, the atmosphere gets less dense, so there are fewer air molecules that are able to collide with the surface

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27
Q

What is speed?

A

How fast you are going

28
Q

What is velocity?

A

Speed in a given direction

29
Q

What is happening to an object moving in a circle at constant speed?

A

It has a constantly changing velocity as the direction is always changing

30
Q

What is the average speed of a person walking?

A

1.5 m/s

31
Q

What is the average speed of a person running?

A

3 m/s

32
Q

What is the average speed of a person cycling?

A

6 m/s

33
Q

What is the average speed of a car?

A

25 m/s

34
Q

What is the average speed of a train?

A

55 m/s

35
Q

What is the average speed of a plane?

A

250 m/s

36
Q

What is uniform acceleration?

A

Constant acceleration e.g. acceleration due to gravity is uniform for objects in free fall

37
Q

What do different distance time graphs tell you about a journey?

A

Gradient = speed, flat = stationary, straight uphill = steady speed, curves = acceleration or deceleration

38
Q

What do different velocity time graphs tel you about a journey?

A

Gradient = acceleration, flat = steady speed, uphill = acceleration, downhill = deceleration, curve = changing acceleration, area under section of graph =distance travelled in time interval

39
Q

How does a driver travel at a steady speed to counteract friction?

A

They need to balance the frictional forces as friction always acts in the opposite direction to movement

40
Q

How do you reduce drag?

A

By keeping the object streamlined as it allows fluids to flow over it easily

41
Q

How do you increase the top speed of a vehicle?

A

Reduce drag by altering the shape and increasing the power of the engine

42
Q

What is terminal velocity?

A

A steady velocity that an object falling reaches after the velocity begins to decrease

43
Q

How would a velocity-time graph look for a falling object?

A

A steep gradient (for the great acceleration) which then levels out and becomes flat, as the object reaches it’s terminal velocity (as the forces are balanced and the object is no longer accelerating)

44
Q

What factors affect terminal velocity?

A

Shape and area, as resistance can play a part in this

45
Q

What is Newton’s first law?

A

If the resultant force on a stationary object is zero, the object will remain stationary but if the resultant force on a moving object is zero, it will keep moving at the same speed but if there is a resultant force on an object non-zero, the velocity will change

46
Q

What changes in velocity can an object experience when a resultant force is acting upon it?

A

Starting, stopping, changing direction, slowing down and speeding up

47
Q

What is Newton’s second law?

A

The larger the resultant force acting upon an object, the larger the acceleration (directly proportional) and acceleration is also inversely proportional to the mass of the object

48
Q

What is inertia?

A

The tendency to keep moving at the same velocity or to continue in the same state of motion

49
Q

What does an objects inertia mass measure?

A

How difficult it is to change the velocity of an object

50
Q

What is Newton’s third law?

A

When two objects interact, the forces they exert on each other are both equal and opposite

51
Q

What is the total stopping distance?

A

The sum of the braking distance and the thinking distance

52
Q

What is the thinking distance?

A

The distance the vehicle travels during the driver’s reaction time

53
Q

What is the braking distance?

A

The distance the vehicle travels after the brakes are applied, before coming to a complete stop

54
Q

What factors affect thinking distance?

A

How fact you are going and your reaction time (could be affected by tiredness or drugs etc.)

55
Q

What factors affect braking distance?

A

How fast you’re doing, how good your brakes are, how good your tires are and how good the grip is (can be affected by weather conditions)

56
Q

How can reaction time be tested?

A

By doing the ruler drop test; the longer the distance caught on, the longer the reaction time

57
Q

What is the typical human reaction time?

A

Between 0.2 s and 0.9 s

58
Q

How can you make the results of an experiment more reliable?

A

Do repeats, then calculate the mean

59
Q

Why do the brakes heat up when used?

A

The brakes rely on friction between the brakes and the wheels, causing work to be done, causing energy transfer from the kinetic energy stores of the wheels to the thermal energy stores of the brakes

60
Q

What is momentum?

A

A property of moving objects; the greater the mass and velocity of an object, the greater the momentum it has

61
Q

What is conservation of momentum?

A

In a closed system, the total momentum before an event is the same as the total momentum after the event

62
Q

What happens to momentum in an explosion?

A

Before the explosion, the momentum is zero and after the explosion, pieces fly in different directions so that the individual momentums of each piece cancel each other out, making the overall momentum zero

63
Q

Why are cars designed to slow people down over a longer period of time in a crash?

A

The longer it takes for a change in momentum, the smaller the rate of change in momentum, and so the smaller the force

64
Q

What safety features do cars have and how do they help?

A

Crumple zones crumple on impact so increase the time taken to stop, seat belts increase the time taken for the wearer to stop and airbags, when inflated, slows you down more gradually

65
Q

How do bike helmets help safety?

A

They contain a crushable layer of foam which helps lengthen the time it takes for your head to stop in a crash, reducing the impact on your brain

66
Q

How do crash mats and cushioned playground flooring help safety?

A

The increase the time taken for you to stop when you fall on them as they are made from soft, compressible materials

Physics paper 2 (3 decks)

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