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physics > forces and motion > Flashcards

forces and motion Flashcards

1
Q

What is speed and velocity?

A

speed - how fast you’re going
velocity - the same w/ direction

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2
Q

What is the formula for average speed?

A

average speed = distance moved / time taken

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3
Q

What is acceleration?

A

how quickly velocity is changing

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4
Q

What is the first formula for acceleration?

A

acceleration = change in velocity / time taken

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5
Q

What is the second formula for acceleration?

A

v^2 = u^2 + 2as

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6
Q

What does the gradient represent in distance-time graphs?

A

speed of the object

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7
Q

What does the flat sections represent in distance-time graphs?

A

where it’s stopped

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8
Q

What does a steeper distance-time graph mean?

A

goes faster

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9
Q

What do curves represent in distance-time graphs?

A

acceleration

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10
Q

What does it mean when a curve gets steeper in distance-time graphs?

A

speeding up (increasing gradient)

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11
Q

What does it mean when a curve levels off in distance-time graphs?

A

slowing down (decreasing gradient)

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12
Q

What does the gradient represent in velocity-time graphs?

A

acceleration

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13
Q

What does the flat sections represent in velocity-time graphs?

A

steady speed

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14
Q

What does a stepper velocity-time graph represent?

A

greater acceleration/deceleration

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15
Q

What do uphill sections in a velocity-time graph represent?

A

acceleration

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16
Q

What do downhill sections in a velocity-time graph represent?

A

deceleration

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17
Q

What does the area in a velocity time graph represent?

A

distance travelled in that time interval

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18
Q

What does a curve in a velocity-time graph represent?

A

changing acceleration

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19
Q

What is another way to find the speed in a distance-time graph?

A

divide the total distance travelled by the time it takes to travel that distance

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20
Q

What is gravity and what does it do (1 - define) (3 characteristic)

A

the force of attraction between all masses
1. makes everything accelerate
2. gives everything a weight
3. keeps planets, moon and satellites in their orbits

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21
Q

What is the acceleration on Earth?

A

9.8 m/s2 or 10m/s2

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22
Q

What is mass and what is it measured in?

A

amount of matter in an object and measured in kg with a mass balance

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23
Q

What is weight and what is it measured in?

A

a measure of the force of gravity on an object and measured in Newtons (measured w spring balance or newton meter)

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24
Q

What is the formula relating weight, mass and gravity?

A

weight = mass x gravitational field strength

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25
Q

What does the force of gravity or weight do?

A

acts straight downwards

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26
Q

What does a reaction force do?

A

acts perpendicular to a surface and away from it (so if the surface is horizontal, it would act straight upward)

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27
Q

What is electrostatic force?

A

the force between charged objects > direction depends on type of charge (like charges repel, opposite charges attract)

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28
Q

What does thrust mean?

A

a push or pull due to an engine or rocket, increasing the speed of the object

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29
Q

What does drag/air resistance/friction mean?

A

slows the object down

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30
Q

What does lift do?

A

helps bring a plan up with pressure (due to an aeroplane wing)

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31
Q

What does tension mean?

A

the strength used when coming or holding the hair that stretches the hair out of its normal shape (rope or cable)

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32
Q

What do objects with a weight feel?

A

a reaction force back from the surface its on. otherwise it would keep falling

33
Q

What happens when an object moves through a fluid?

A

it feels drag in the opposite direction of its motion

34
Q

Why do objects slow down and stop?

A

if the object has no force acting on it, friction slows it down

35
Q

What is friction?

A

a force that opposes motion

36
Q

What is the first out of the three ways that friction occurs?

A

static friction - when friction happens between solid surfaces which are gripping

37
Q

What is the second out of the three ways that friction occurs?

A

sliding friction - when friction happens between solid surfaces which are sliding past each other

38
Q

What is the third out of the three ways that friction occurs?

A

resistance or drag from fluids - in a fluid friction always increases as the speed increases

39
Q

What is the first law of motion?

A

balanced forces mean no change in velocity

40
Q

State the relationship between an object moving at constant speed and its forces

A

when an object moves at a constant velocity, the forces must all be balanced

41
Q

What is needed to go at a steady speed?

A

zero resultant force

42
Q

What is the second law of motion?

A

a resultant force means acceleration - if there’s an unbalanced force, then the object will accelerate in that direction

43
Q

What will a resultant force always produce?

A

acceleration

44
Q

State the 5 ways acceleration can occur

A
  1. starting
  2. stopping
  3. speeding up
  4. slowing down
  5. changing direction
45
Q

What is the formula of resultant force?

A

resultant force = mass x acceleration

46
Q

What is the third law of motion?

A

for every action there is an equal and opposite reaction

47
Q

Why is it easier to stop an empty trolley than a full trolley over the same amount of time?

A

the empty trolley has a smaller mass, so less force is needed to cause the same deceleration and so to stop the trolley

48
Q

What are vectors? Give examples.

A

quantities that have size and direction
- forces, velocity, momentum

49
Q

What are scalars? Give examples.

A

quantities that only have a size
- volume, density, speed, energy, mass and time

50
Q

How can we work out the resultant force?

A

add the vectors

51
Q

What is terminal velocity

A

the greatest velocity a falling object reaches

52
Q

What happens when an object starts to fall? (4)

A
  1. the object has much more force accelerating it than resistance slowing it down
  2. as the velocity increases, the resistance builds up
  3. the resistance force gradually reduces the acceleration until the resistance force equals the accelerating force
  4. at this point, the object can’t accelerate so it reaches its terminal velocity
53
Q

What happens when an object starts to fall? (7)

A
  1. When an object first starts to fall, it undergoes free fall and accelerates due to the force of gravity, as there is no initial air resistance.
  2. The object experiences much more force accelerating it than resistance slowing it down in the absence of air resistance.
  3. As the velocity of the falling object increases, it encounters air resistance (drag), which opposes its motion.
  4. The drag force gradually builds up with the square of the velocity, becoming more pronounced as the object descends.
  5. The resistance force steadily reduces the object’s acceleration until it reaches a point where the resistance force equals the force of gravity.
  6. At this equilibrium point, the object can no longer accelerate, and it attains its terminal velocity.
  7. Terminal velocity is the constant speed achieved when the drag force matches the force of gravity, resulting in a dynamic balance between acceleration and resistance.
54
Q

What does the terminal velocity of falling objects depend on?

A

shape and area

55
Q

What does air resistance cause?

A

objects to fall at different speeds

56
Q

What is the terminal velocity of an object determined by?

A

the objects drag compared to its weight

57
Q

Explain how terminal velocity occurs in a human skydiver (4)

A
  1. he has a small surface area when his parachute isn’t open and a force is equal to his weight, pulling him down
  2. he reaches a terminal velocity of 120 mph
  3. but w his parachute open, there’s much more air resistance
  4. once he reaches his terminal velocity, (RESISTANCE = WEIGHT) > his terminal velocity is 15 mph
58
Q

Explain why an object falling through the air will eventually stop accelerating (9)

A
  1. Initially, when an object falls through the air, it experiences acceleration due to the force of gravity.
  2. As the object gains velocity during its descent, it encounters air resistance, also known as drag.
  3. Air resistance acts in the opposite direction to the object’s motion and increases with the square of the object’s velocity.
  4. The force of air resistance becomes more pronounced as the object accelerates.
  5. There comes a point where the force of air resistance equals the force of gravity pulling the object downward.
  6. At this equilibrium point, the net force acting on the object becomes zero.
  7. The object reaches a state of constant velocity, known as terminal velocity.
  8. Terminal velocity is the maximum speed a falling object can achieve when the opposing forces of gravity and air resistance reach a dynamic equilibrium.
  9. At terminal velocity, there is no further net acceleration, and the object continues to fall at a steady speed.
59
Q

Explain why a skydiver falls slowly after they’ve opened their parachute (2)

A
  1. the open parachute leads to the resistance force equalling the skydiver’s weight at a much lower speed than before the parachute was open
  2. this means the skydiver falls slower after they open the pararchute
60
Q

What is Hooke’s law?

A

extension is proportional to force

61
Q

What is natural length?

A

the length of an unstretched metal wire

62
Q

In Hooke’s law, what produces an equal and opposite force? (2)

A
  1. if a metal wire is supported at the the top and then a weight is attached at the bottom, it stretches.
  2. the weight pulls down with force producing an equal and opposite force at the support
63
Q

Where does the production of an equal and opposite force also happen?

A

helical springs and any object that will stretch without immediately snapping or deforming

64
Q

What will obey Hooke’s Law?

A

a metal spring if a pair of opposite forces are applied to each end

65
Q

What supplies are needed to investigate Hooke’s Law with a spring? (5)

A
  • clamp
  • spring
  • hanging mass
  • weighted stand
  • extra masses
66
Q

How can you investigate Hooke’s Law with a spring? (1-3)

A
  1. set up the apparatus as as shown to the right. ensure you measure the weight of each extra masses (w a balance)
  2. measure the length of the spring when no load is applied. ensure the ruler is vertical and measure the spring at eye level (spring’s natural length)
  3. add one mass at a time and allow the spring to come to rest, then measure the new length of the spring. the extension is the change in the length from the original length. adding a marker to the top and bottom of the spring might make measuring lengths easier. repeat this process until you have enough measurements
67
Q

How can you investigate Hooke’s Law with a spring? (4-6)

A
  1. once done, repeat the experiment and calculate an average value for the length of the spring for each applied weight
  2. plot your results on a graph - show force on the y axis and total extension on the x axis. you should see that the same increase in the weight on the end of the spring always leads to the same increase in extension
  3. repeat the experiment using a metal wire or rubber band instead of spring
68
Q

How can you investigate Hooke’s Law with a spring? (6)

A
  1. set up the apparatus as as shown to the right. ensure you measure the weight of each extra masses (w a balance)
  2. measure the length of the spring when no load is applied. ensure the ruler is vertical and measure the spring at eye level (spring’s natural length)
  3. add one mass at a time and allow the spring to come to rest, then measure the new length of the spring. the extension is the change in the length from the original length. adding a marker to the top and bottom of the spring might make measuring lengths easier. repeat this process until you have enough measurements
  4. once done, repeat the experiment and calculate an average value for the length of the spring for each applied weight
  5. plot your results on a graph - show force on the y axis and total extension on the x axis. you should see that the same increase in the weight on the end of the spring always leads to the same increase in extension
  6. repeat the experiment using a metal wire or rubber band instead of spring
69
Q

What is elastic limit?

A

maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation

70
Q

What happens if you increase the force past the elastic limit?

A

the material will be permanently stretched and when all the force is removed, the material will be longer than at the start

71
Q

What are factors that affect total stopping distance? (4)

A
  • speed of car
  • mass of car
  • how worn the brakes and tyres are
  • road surface
72
Q

What is the formula for stopping distance?

A

stopping distance = thinking distance + braking distance

73
Q

What is thinking distance?

A

the distance travelled by the vehicle in the time it takes the driver to react

74
Q

What are two factors that affect thinking distance?

A
  • your speed
  • your reaction time
75
Q

What factors affect your reaction time? (4)

A
  • tiredness
  • drugs
  • alchohol
  • old age
76
Q

What is braking distance?

A

distance your car travels after yoi apply the brakes

77
Q

What is braking time?

A

time it takes for the brakes and friction between the road and tires to stop the vehicle

78
Q

What factors affect your braking distance (4)

A
  1. your speed - faster ur going = further it takes to stop
  2. mass of vehicle - larger the mass = longer it takes to stop
  3. quality of brakes
  4. quality of grip - (depends on 3 things: road surface, weather conditions, road tyres)

physics (6 decks)

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