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Physics > Topic 5: Forces > Flashcards

Topic 5: Forces Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

Define a ‘force’

A

A push or pull that acts on an object due to the interaction with another object

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2
Q

What is a contact force?

A

Objects are physically touching

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3
Q

What is a non-contact force?

A

Objects that are physically separated?

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4
Q

4 examples of contact forces

A

Friction, air resistance, tension and normal contact force

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5
Q

3 examples of non-contact forces

A

gravitational, electrostatic and magnetic

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6
Q

Define a ‘scalar’ quantity

A

A quantity with magnitude only

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7
Q

Define a ‘vector’ quantity

A

A quantity with magnitude and direction

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8
Q

What does the length of a vector arrow show?

A

Magnitude

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9
Q

3 examples of vector quantities

A

Force, velocity and displacement

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10
Q

3 examples of scalar quantities

A

Speed, distance, mass

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11
Q

What is ‘resultant force’

A

The overall force acting on an object

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12
Q

Define ‘equilibrium’

A

When all of the forces on an object balance out

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13
Q

Elasticity

Why to change the shape of an object, do you need more than one force?

A

The object would move in the direction of the applied force, instead of changing shape

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14
Q

What does it mean if an object has been ‘elastically deformed’?

A

It will go back to its original shape and length (after force has been removed)

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15
Q

What does it mean if an object has been ‘inelastically deformed’?

A

Doesn’t go back to its original shape and length (after force has been removed)

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16
Q

What does the ‘limit of proportionality’ mean?

A

When force and extension are no longer directly proportional (Hooke’s Law)

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17
Q

What does a lower ‘spring constant’ mean?

A

The object is more elastic

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18
Q

What does a higher ‘spring constant’ mean?

A

The object is more stiff

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19
Q

Define a ‘moment’

A

The turning effect of a force

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20
Q

In terms of moments, what does it mean if an object is balanced?

A

Total clockwise moment = total anticlockwise moment

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21
Q

Briefly explain how levers work [3]

A
  1. Levers increase the distance from the pivot at which a force is applied
  2. Since M = Fd this means less force is needed to get the same moment
  3. This means levers make it easier to work
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22
Q

What are gears used for?

A

To transmit the rotational effect of a force from one place to another

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23
Q

What will a force transmitted to a larger gear do and why?

A

Will cause a bigger moment because the distance from the pivot is greater

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24
Q

p = hpg

What 3 factors affect pressure in liquids?

A

height of liquid above object, density of liquid and gravity

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25
Q

Explain ‘upthrust’ [3]

A
  1. A submerged object experiences a greater pressure on the bottom surface than the top surface
  2. This creates a resultant force upwards
  3. This force is called upthrust
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26
Q

Describe the 2 circumstances which cause an object to sink

A
  1. Weight is greater than the upthrust
  2. The object is denser than the fluid
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27
Q

Describe the 2 circumstances which cause an object to float

A
  1. Weight is less than the upthrust
  2. The object is less dense than the fluid
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28
Q

What happens to the atmospheric pressure as altitude increases?

A

It decreases

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29
Q

Explain why atmospheric pressure decreases as altitude increases? [4]

A
  1. As the altitude increases, the atmosphere gets less dense
  2. Therefore, there are less air molecules able to collide with the surface
  3. There are also fewer air molecules above the surface as height increases
  4. This means that the weight of air above it, which contributes to atmospheric pressure, decreases with altitude
30
Q

What kind of quantity is distance and why?

A

Scalar. Does not involve direction

31
Q

What kind of quantity is displacement and why?

A

Vector. It involves magnitude (distance) and direction

32
Q

What kind of quantity is speed and why?

A

Scalar. Does not involve direction

33
Q

What kind of quantity is velocity and why?

A

Vector. It involves magnitude (speed) and direction

34
Q

Typical value of walking

A

1.5 m/s

35
Q

Typical value of running

A

3 m/s

36
Q

Typical value of cycling

A

6 m/s

37
Q

Typical value of a car

A

25 m/s

38
Q

Typical value of a train

A

30 m/s

39
Q

Typical value of a plane

A

250 m/s

40
Q

Typical value of sound in air

A

330 m/s

41
Q

When calculating acceleration, if an object is dropped, what will its acceleration be?

A

9.8 m/s² (gravity)

42
Q

What do straight uphill sections represent on a distance/time graph?

A

Steady speed

43
Q

What do **flat **sections represent on a distance/time graph?

A

Stationary

44
Q

What do curves represent on a distance/time graph?

A

Acceleration/deceleration

45
Q

What does the gradient of a line on a distance/time graph represent?

A

Speed

46
Q

How do you find** acceleration** at a specific point on a distance/time graph?

A

Draw a tangent to the line

47
Q

What do flat sections on a velocity/time graph represent?

A

Steady speed

48
Q

What do uphill sections represent on a velocity/time graph?

A

Constant acceleration

49
Q

What do downhill sections represent on a velocity/time graph?

A

Constant deceleration

50
Q

What does a curve represent on a velocity/time graph?

A

Changing acceleration

51
Q

What does the gradient of a line on a distance/time graph represent?

A

Acceleration

52
Q

How do you calculate the distance travelled on a velocity/time graph?

A

Calculate the area under the graph

53
Q

Write on paper and check

Explain what happens when a person jumps out of an aeroplane (up until 1st terminal velocity) [6]

A
  1. When the person starts falling, their weight downwards is much larger than any air resistance upwards
  2. There is a resultant force in the downwards direction, causing the person to accelerate
  3. As the person accelerates and their velocity increases, the air resistance also increases
  4. The resultant force downwards gets smaller
  5. At some point, the air resistance will equal the person’s weight
  6. There is no resultant force, the person does not accelerate and they have reached terminal velocity
54
Q

Write on paper and check

Explain what happens when a person opens their parachute (reaching 2nd terminal velocity) [6]

A
  1. As the parachute is opened, the SA is increased
  2. Therefore, the air resistance would increase
  3. The resultant force would now be upwards and the person would accelerate upwards and slow down
  4. The slower the person is falling, the lower the air resistance
  5. The resultant force upwards would get smaller and smaller
  6. Eventually the air resistance would become equal to the weight and the person would have reached a new, lower terminal velocity
55
Q

Think: skydiver

What does the size of air resistance depend on? [2]

A

SA, velocity

56
Q

What is Newton’s 1st law of motion?

A

A resultant force is required to change the motion of an object

57
Q

What is Newton’s 2nd law of motion?

A

If a non-zero resultant force acts on an object, then it will cause the object to accelerate

58
Q

Define ‘inertia’

A

The tendancy for the motion of an object to remain unchanged

59
Q

What is Newton’s 3rd law of motion?

A

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

60
Q

What is stopping distance a sum of?

A

Thinking distance + braking distance

61
Q

What affects thinking distance? [2]

A

Speed and reaction time

62
Q

What affects braking distance? [4]

A
  1. Speed
  2. Weather/road surface
  3. Condition of tyres
  4. Quality of brakes
63
Q

What is the typical range of a person’s reaction time?

A

0.2 - 0.9 s

64
Q

Does speed affect thinking or braking distance more?

A

Braking distance

65
Q

What is the ‘conservation of momentum’?

A

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

66
Q

Explain how crumple zones work [2]

A
  1. Crumple zones crumple on impact
  2. Increases the time taken for the car to lose its momentum
67
Q

Explain how seat belts work [4]

A
  1. Seat belts stretch slightly
  2. Increases the time taken for the person to lose momentum
  3. Results in a lower force acting on the person
  4. Less likely to be injured
68
Q

Explain how air bags work [4]

A
  1. Air bags inflate before you hit the dashboard of a car
  2. The compressing air inside it increases the time taken for you to lose momentum
  3. Results in a lower force acting on the person
  4. Less likely to be injured
69
Q

Explain how bike helmets work [4]

A
  1. Bike helmets contain a crushable layer of foam
  2. Increases the time taken for the person’s head to lose momentum
  3. Results in a lower force acting on the person
  4. Less likely to be injured (head)
70
Q

Explain how crash mats/playground flooring works [4]

A
  1. Made from soft, compressible material
  2. Increases the time taken for you to lose momentum
  3. Results in a lower force acting on the person
  4. Less likely to be injured

Physics (8 decks)

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