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Physics > Motion Graphs and Forces > Flashcards

Motion Graphs and Forces Flashcards

1
Q

what does the gradient represent on a distance/time graph?

A

the gradient is equal to the speed of the object (velocity)

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2
Q

what is the equation for speed?

A

distance ÷ time

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3
Q

what is the equation for the average speed?

A

total distance ÷ total time

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4
Q

what does the gradient of a velocity/time graph represent?

A

the gradient is equal to the acceleration of the object

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5
Q

how do you work out the distance travelled on a velocity/time graph?

A

look at the area under the gradient

e.g. if it makes a triangle under the line you then do 1/2 x base x height to work out the distance

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6
Q

what is the units for velocity?

A

m/s

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7
Q

what is the units for acceleration?

A

m/s2

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8
Q

if a ticker tape timer produces dots at a frequency of 50Hz, how many dots are produced per second?

A

50

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9
Q

on a ticker tape timer, how can you tell if the dots are moving at a constant speed?

A

the dots are equally spready apart

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10
Q

on a ticker tape timer, how can you tell if the dots accelerating?

A

the dots will get further apart

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11
Q

on a ticker tape timer, how can you tell if the dots decelerating?

A

the dots will get closer together

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12
Q

what is aceleration?

A

the rate of change of velocity

rate of change = 1/t

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13
Q

what is the equation for acceleration?

A

a = v - u ÷ t ( v = final velocity, u = initital velocity)

change in velocity ÷ time taken

a = Δv ÷ t = m/s x 1/s = m/s2

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14
Q

how do velocity and acceleration act in decelration?

A

in opposite directions causing the velocity to get smaller

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15
Q

what is a scaler quantity?

A

quantities that have magnitudes or a size only

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16
Q

what is a vector quantity?

A

quantities that have magnitude and direction

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17
Q

give some examples of scalars

A

mass

temprature

distance

time

speed

energy

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18
Q

give some examples of vectors

A

velocity

force

weight

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19
Q

what is Newton’s first law?

A

objects will remain at rest or continue to move at a constant speed unless acted upon by a resultant force

if F=0 a =0m/s2

(F = resultant force)

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20
Q

what is Newtons second law?

A

resultant force is directly proportional to the rate of change of momentum

F∝ mv - mu ÷ t

(F = resultant force, ∝ = directly proportional, t = rate of change, mv - mu = momentum)

F = mv-mu ÷ t

F = m (v-u) ÷ t [acceleration]

F= ma

resultant force = mass x acceleration

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21
Q

what are the units used in the equation for Newton’s second law?

A

resultant force = mass x acceleration​

F = ma

F = resultant force (N)

m = mass (kg)

a = acceleration (m/s2)

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22
Q

what is static friction?

A

the friction acting on stationairy objects

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23
Q

what is dynamic friction?

A

the friction acting on moving objects

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24
Q

what is the control variable?

A

something that is constant and unchanged

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25
Q

what is thinking distance?

A

the distance a vehicle travels while the driver is reacting

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26
Q

what is breaking distance?

A

the distance a vehicle travels while the brakes are being applied until it stops

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27
Q

what is stopping distance?

A

thinking distance + breaking distance

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28
Q

give some factors that affect thinking distance

A

use of alcohol

use of drugs (il/legal)

distracted by passengers in the vehicle

tired

using a mobile

speed of car

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29
Q

give some factors that affect braking distance

A

mass of car

weather

tread of tyres

wornout breakes

level of grip on road

speed of car

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30
Q

if the distance = 8,000m and the time = 3,600s, calculate the average speed

A

average speed = total distance ÷ total time

= 8000 ÷ 3600

=2.2 m/s

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31
Q

describe the motion of a on this distance/time graph

A

a is stationairy because the gradient is a straight, vertical line

we did not move it we just let the device play

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32
Q

describe the motion of e on this distance/time graph

A

e is accelerating away from the origin

there is no constant speed

we started the pencil case at the device (origin) and then accelerated it away

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33
Q

describe the motion of b and c on this distance/time graph

A

b is moving fast at a constant speed

c is moving fast at a consant speed but faster than b, almost double

to achieve this graph we flipped the sensor from its side to face upwards and we moved a pencil case upwards and away from it in a constant motion

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34
Q

describe the motion of f on this distance/time graph

A

f is movimg at a fast away from the device (origin) and constant pace but then remains stationairy at a point

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35
Q

describe the motion of a on this velocty/time graph

A

a is moving at a constant speed

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36
Q

describe the motion of d on this velocity/time graph

A

d is deccelerating at a constant rate

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37
Q

describe the motion of b and c on this velocity/time graph

A

b is acelerating at a constant rate

c is acelerating at a constant rate faster than b

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38
Q

in equilibrium or when stationionairy or moving a constant speed, what is the resultant force?

A

0N

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39
Q

calculate the resultant force and the accelertaion of this 5.0kg mass

A

F = 1050-895

= 155N (downwards)

as F = ma

a = F ÷ m

= 155÷5

= 31 m/s2

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40
Q

calculate the resultant force and the accelertaion of this 5.0kg mass

A

F = 100 + (-80)

= 20N (to the left)

as F = ma

a = F ÷ m

= 20 ÷ 5

= 4 m/s2 (to the left)

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41
Q

calculate the resultant force and the accelertaion of this 5.0kg mass

A

F = 10 + (-15)

= 5N (downwards)

as F = ma

a = F ÷ m

= 5 ÷ 5

=1 m/s2

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42
Q

calculate the resultant force and the accelertaion of this 5.0kg mass

A

F = 100 + (-500)

= 400N (downwards)

as F = ma

a = F ÷ m

= 400 ÷ 5

=80m/s2 (downwards)

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43
Q

what is the reaction time of the driver?

A

0.6 seconds

44
Q

calculate the thinking distance

A

area of the rectangle (imagine this)

20 x 0.6

= 12m

45
Q

how long did the car brake for?

A

2.8-0.6

= 2.2 secs

46
Q

calculate the braking distance

A

area of triangle

0.5 x 20 x 2.2

= 22

47
Q

calculate the stopping distance if it has been previously worked out that the thinking distance is 12m and the braking distance is 22m

A

22 + 12

= 34m

48
Q

in terms of energy, what do brakes do to a car?

original kinetic energy = 400,000J

final kinetic energy = 0J

A

kinetic energy is converted into heat and sound which is then disipitated into the atmosphere

the brake pads do work

kinetic energy –> heat + sound

49
Q

if Fd = change in Ek, calculate the average braking force (F) produced by the brakes

kinetic energy = 400,000J

braking distance = 22m

A

d = braking distnace = 22

Ek = 400,000J

F = Ek ÷ d

= 400,000 ÷ 22

= 18181.81 N

50
Q

when giving an acceleration, what must it have?

A

a direction

e.g. downwards, to the left

51
Q

complete this skydiver velocity/time graph

A
52
Q

state the value or direction of the resultant force at A

A

Resultant force is acting dowanwards because weight is the only force acting on the sky diver

towards the ground (downwards)

53
Q

state the value or direction of the resultant force at B

A

resultant force is decreasing yet it still acting downwards because air resistance is increasing

54
Q

state the value or direction of the resultant force at C

A

resultant force is zero

the skydiver has reached terminal velocity

because the graident and acceleration is zero

55
Q

state the value or direction of the resultant force at D

A

resultant force is acting upwards (velocity acting down, accelerating upwards)

because he is rapidly deccelertaing

56
Q

state the value or direction of the resultant force at E (end of graph parachute)

A

resultant force is zero as the sky diver has reached a new terminal velocity

because the gradient and acceleration is zero

57
Q

the weight of an object is the force of ……which acts on it

A

gravity

58
Q

when you drop something, first of all it …..

A

acelerates

59
Q

the faster an object falls, the bigger force of ……. which acts on it

A

friction

60
Q

eventually a dropped object will …….

A

fall at a steady speed

61
Q

which force is the foward force from the engine?

which force is the force resisting the van’s motion?

A

A is the foward force

E is the force resisting motion

62
Q

complete this table

A
63
Q

complete the following paragraph to explain why seatbelts reduce the risk of injury if the van stops suddenly

a large …. is needed to stop the van suddenly

the driver and passengers would continue to move …..

the seatbelts supply a …. force to keep the driver and passengers in their seats

A

a large force is needed to stop the van suddenly

the driver and passengers would continue to move fowards

the seatbelts supply a backwards force to keep the driver and passengers in their seats

64
Q

if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the acceleration of the car during the 11 scesonds

A

a = v-u ÷ t

= 33 - 0 ÷ 11

= 3m/s2

65
Q

if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the force needed to produce this acceleration

A

F = ma

= 950 x 3

=2850 N

66
Q

The manufactor of a car claims a top speed of 110 miles per hour. Explain why there must be a top speed for a car

A

the air resistance will increase directly proportionally to the speed

the car cannot accelerate forever, it must reach a resultant force

everntually the engine force will = air resistance

67
Q

a driver may have to make an emergency stop

give three factors which affect their thinking distance or braking distance

A

use of alcohol affects thinking distance as it slows down you reaction time. this affects your stopping distance as stopping distance = thinking + braking distance. if your thinking distance increases, so will your stopping distance

being distracted by the passengers in the car will affect thinking disatnce as you aren’t focused and your reaction time is delayed - this increased stopping distance as they are connected

worn out brakes will affect your braking distances as the efficiency of the brakes decreases . friction will act in opposite motion to the tyres, increasing the braking distance. as braking distance increases, so does stopping

68
Q

what does the acceleration of a car depend on?

A

the force applied by the engine and the mass of the car

69
Q

the velocity of a car is its speed in a particular ……

A

direction

70
Q

what part of the graph represents thinking time of the driver and what is this time in seconds?

A

A - B

0.7 seconds

71
Q

calculate the distance travelled by the car in thinking time

A

area of rectangle

0.7 x 24

= 16.8m

72
Q

calculate the acceleration of the car after the brakes are applied

A

a = v - u ÷ t

= 24 ÷ t

= -6 m/s2

73
Q

calculate the distance travelled by the car during braking

A

are under the traingle

4x 24 ÷ 2

= 48m

74
Q

the mass of the car is 800kg

calculate the braking force

A

F = ma

= 800 x -6

= - 4800 N

75
Q

Explain the motion of a skydiver

A

Before the parachute opens:

  1. When the skydiver jumps out of the plane he accelerates due to the force of gravity pulling him down.
  2. As he speeds up the upwards air resistance force increases. He carries on accelerating as long as the air resistance is less than his weight.
  3. Eventually, he reaches his terminal speed when the air resistance and weight become equal. They’re said to be balanced.

After the parachute opens:

  1. When the canopy opens it has a large surface area which increases the air resistance. This unbalances the forces and causes the parachutist to slow down.
  2. As the parachutist slows down, his air resistance gets less until eventually it equals the downward force of gravity on him (his weight). Once again the two forces balance and he falls at terminal speed. This time it’s a much slower terminal speed than before.
76
Q

Look In Experiment Write-Ups:

describe an experiment to investigate friction

A
77
Q

Define resultant force

A

the sum forces acting on an object

78
Q

What is the equation that links gravity, mass and weight?

A

weight (N) = mass (kg) x gravity (N/kg)

79
Q

What are the units for force?

A

Newtons (N)

80
Q

What are the units for acceleration?

A

Metres per second2 (m/s2)

81
Q

What are the units for gravity?

A

Netwong per kilogram (N/kg)

82
Q

What are the units for mass?

A

Kilograms (kg)

83
Q

A force is simply a … or a …

A

A force is simply a push or a pull

84
Q

What are the twelve different types of forces you need to know?

A

gravity

weight

reaction force

electrostatic force

thrust

push

pull

drag

air resistance

friction

lift

tension

85
Q

Gravity or weight always act …

A

Gravity or weight always act straight downwards

86
Q

Reaction force from a surface usually acts …

A

Reaction force from a surface usually acts straight upwards

87
Q

The direction of electrostatic force between two charged objects depends on …

A

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

88
Q

Thrust or push or pull speeds/slows something up/down

A

Thrust or push or pull speeds something up

89
Q

Drag or air resistance or friction speeds/slows something up/down

A

Drag or air resistance or friction slows something down

90
Q

Lift acts on …

A

Lift acts on aeroplane wings

91
Q

Tension acts in a … or …

A

Tension acts in a rope or cable

92
Q

What four forces are acting on a moving car?

A
93
Q

If an object has no force propelling it foward, it will always slow down and stop because of …

A

If an object has no force propelling it foward, it will always slow down and stop because of friction

94
Q

What is friction?

A

friction is a force that opposes motion

95
Q

In what three main ways does friction occur?

A

Friction betwen solid surfaces which are gripping (static friction)

Friction between solid surfaces which are sliding past each other

Resistance or ‘drag’ from fluids (liquids or gases)

96
Q

How do you reduce:

Friction betwen solid surfaces which are gripping (static friction)

Friction between solid surfaces which are sliding past each other

A

by putting a lubricant, like oil or grease, between the surfaces

97
Q

In a fluid, friction always increases as the speed …

A

In a fluid, friction always increases as the speed increases

98
Q

Explain how moving objects reach a terminal velocity

A

Wehn objects first set off they have much more force accelerating them than resistance slowing them down

As the velocity increases, the resistance increases

This gradually reduces the acceleration until eventually the resistance is equal to the accelerating force and then it won’t be able to accelerate any more - it will have reached its terminal velocity

99
Q

How can you investigate falling objects using sycamore seeds?

A
  1. Sycamore seeds have a small wieght and a large surface area so they reach terminal velocity really quickly and fall slowly
  2. Collect a bunch of sycamore seeds of different sizes and measure the mass and wing length of each one. Use an accurate ruler and repeat each measurement several times to make sure it’s accurate. Use all the seeds that have similar masses but different wavelengths
  3. Drop each of the seeds from the same height and use a stopwatch to find how long each one takes to fall to the ground. The higher you drop them the better - it gives a larger measurement and so improves the accuracy of the measurement
  4. Repeat the experiment for each seed and find an average time
  5. Plot a graph of length of the wings (x) against the time taken to hit the floor (y). This will tell you if there is a relationship between the shape of the sycamore seeds and their terminal velocity
  6. Bigger wings means bigger surface area and so higher drag. Higher drag means lower terminal velcoty, and so the seeds fall more slowly
100
Q

Explain the relationship between drag (air resistance) and weight during terminal velocity

A

during terminal velocity, weight = drag (air resistance)

101
Q

What is Newton’s Third Law?

A

if object A exerts a force in object B then object B exerts the exact opposite force on object A

102
Q

Objects … when the resultant force is positive

Objects … when the resultant force is negative

A

Objects accelerate when the resultant force is positive

Objects decelerate when the resultant force is negative

103
Q

Be able to describe the motion of objects on a distance/time graph

A
104
Q

Be able to describe the motion of objects on a velocity/time graph

A
105
Q

Describe an experiment to investigate the motion of a toy car on a ramp

A
  1. Mark a line on the ramp - this is to make sure the car starts from the same point each time
  2. Measure the distance between each light gate - you’ll need this to find the car’s average speed
  3. Let go of the car just before the light gate so that it starts to roll down the slope
  4. Let go of the car just before the light gate so that it starts to roll down the slope
  5. The light gates should be connected to a computer. When the car passes through each light gate, a beam of light is broken and a time is recorded by a data-logging software
  6. Repeat this experiment several times and get an average time for the car to reach each light. This will make your results more reliable
  7. Using these times and distances between lightgates you can find the average speed of the car on the ramp and the average speed of the car on the runway

Physics (24 decks)

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