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edexcel igcse physics > unit one: forces and motion > Flashcards

unit one: forces and motion Flashcards

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1
Q

torque (turning effect) unit

A

newton meter (Nm)

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2
Q

momentum unit

A

kilogram metre per second (kg m/s)

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3
Q

acceleration unit

A

metre per second squared

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4
Q

force unit

A

newton (N)

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5
Q

gravitational field strength unit

A

newton per kilogram (N/kg)

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6
Q 
average speed (m/s) =
v =
A 
distance moved (m)  / time (s)
s / t
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7
Q

v =

A

s / t

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8
Q

how do you convert seconds into hours

A

multiply by 60 and then multiply by 60

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9
Q

how do you convert m/s into km/h

A

(multiply by 60 twice and then divide. by 1000) multiply by 3.6

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10
Q

on a distance time graph, how do you calculate the speed

A

speed = gradient

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11
Q

what does a curved line on a distance time graph mean

A

the speed or velocity is changing

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12
Q

what is a vector

A

a quantity with magnitude and direction

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13
Q

if the line on a distance time graph slopes down to the right what is it

A

a negative slope or negative gradient.

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14
Q

average velocity =

A

increase in displacement / time taken

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15
Q

practical: how would you investigate motion using a toy car

A

roll a car down a ramp and use the equation ( v=s/t) to calculate the speed. you will need to measure the height of the raised end of the wooden track every time you change height.

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16
Q

acceleration def

A

the rate at which objects change theri velocity

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17
Q

acceleration (m/s squared) =

a =

A

(final velocity - initial velocity) / time (s)

(v - u) / t

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18
Q

why is u the symbol for initial velocity

A

it comes before v

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19
Q

what does a negative acceleration mean

A

its a deceleration

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20
Q

velocity =

v =

A

distance / time

s / t

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21
Q

how do you find the gradient of a velocity time graph

A

divide the increase in velocity by time taken to do the increasee

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22
Q

how do you find the acceleration of an object from a velocity time graph

A

calculate the gradient of the line by (v-u)/t

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23
Q

how do you find the distance travelled from a velocity time graph

A

either calculate the area underneath the the line or use the equation: (u +v) / 2

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24
Q

scalar

A

a quantity which only has magnitude and no direction

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25
Q

forces acting on a car

A

push by a man or engine
normal reaction
weight (downward pull of gravity)
friction

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26
Q

a force of one newton will make a mass of one kilogram accelerate at…

A

one metre per second

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27
Q

if the forces add to zero will the object move

A

no there has to be a resultant force

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28
Q

how do you work out resultant force

A

add all the forces (but subtract the ones going in the OTHER direction.)

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29
Q

what is friction

A

the force that causes moving objects to slow down and finally stop. the kinetic energy of the moving object is transferred to heat as work is done by the friction force

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30
Q

when does friction occur

A

when solid objects rub up against eachother

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31
Q

brittle

A

materials that break rather than stretching and do not return to their orginal shape

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32
Q

elastic

A

materials that dont break easily and stretch. they return to their original shape

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33
Q

plastic

A

materials that dont break often but change shape and dont go back to their original shape

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34
Q

what happens if you stretch a spring too mucuh

A

it wont return to its original shape and length

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35
Q

hookes law

A

the extension of a spring is proportional to the force of the spring

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36
Q

practical: investigate how the extension of. a spring changes with load

A

attach the spring to a retort stand and clamp with ruler behind it. attach weights to the end of it and plot the extension of the spring to the load on a graph. if it goes through the origin ten it obeys hooked law

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37
Q

do rubber bands obey hookes law

A

no

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38
Q

an object will not change its velocity (accelerate) unless

A

there is an unbalanced force acting on it

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39
Q

how would you investigate the acceleration of a trolley going down a ramp

A

take a series of pictures at equal time intervals using a digital video camera, or use a data logger

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40
Q

if force vs acceleration shows a straight line goi no through the origin what does it ean

A

the force is proportional to acceleration

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41
Q

force =

F =

A

mass x acceleration

m x a

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42
Q

what does breaking distance depend on

A

weight, tread of wheels, dry road

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43
Q

what is thinking distance

A

the distance travelled during the time. for the driver to respond to the new situation before taking any action

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44
Q

what is breaking distance

A

the time it takes for the vehicle to stop

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45
Q

what does thinking distance depend on

A

alchol, drugs, visibility, tiredness, distraction

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46
Q

weight (N) =

W =

A

mass (kg) x gravitational field strength (N/kg)

m x g

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47
Q

what is drag coefficient

A

a measure of how easily an object moves through air

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48
Q

what forces does an object falling through air experience

A

air resistance/drag/ weight force

opposing drag force

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49
Q

what is terminal velocity

A

when there is no longer an unbalanced force because the drag force has increased to the point where it exactly balances the weight force, so its acceleration is 0. however it is still falling, it just cant get faster

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50
Q

the size of drag forces in liquids are much ______ than in gases

A

higher

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51
Q

current unit

A

amperes (A)

52
Q

charge unit

A

coulomb (C)

53
Q

resistance unit

A

ohm

54
Q

voltage unit

A

volts (V)

55
Q

power unit

A

watts (W)

56
Q

purpose of the earth wire

A

to protect you if an appliance develops a fault by. providing a path fo current to escape through the user

57
Q

voltage supplied to homes in the UK

A

230 V

58
Q

what is a fuse

A

a cylinder or cartridge whcih obtains a thin piece of wire made from a metal with a low melting point

59
Q

what is the fuse there for

A

if there is too large a current then the fuse wire becomes very hot and melts. the circuit is now incomplete and reduces the chance of getting a shock or electrical fire

60
Q

size of fuses

A

3A
5A
13A

61
Q

why do many appliances have a metal casing

A

if the live wire becomes damaged or breaks and comes into contact with the casing the earth wire provides a low resistance path for the current, which would probably be big enough to blow the fuse and turn the circuit off.

62
Q

where should a switch always be placed and why

A

in the live wire so when the switch is o pen no energy in the form of electricity can reach an appliance. if the switch is placed in the neutral wire, energy can still enter a faulty appliance and possibly cause an electric shock

63
Q

if we want wires to become warm (heating elements) what do they have

A

high resistance

64
Q

if we dont want wires to become warm what do they have

A

low resistance

65
Q

why will a 70J bulb be brighter than a 50@ oe

A

it transfers 70J of electrical energy every second as opposed to 50J

66
Q

what is power measured in

A

joules per second or watts

67
Q

1kW is

A

1000W

68
Q

power (W) =

P =

A

current (A) x voltage (V)

I x V

69
Q

energy (J) =

E =

A

power (W) x time (s)

P x t

70
Q

direct current

A

current/voltage that isi always in the same direction and have the same value. on a graph it would be a straight line

71
Q

alternating current

A

an electric current that reverses its direction many times a second at regular intervals, typically used in power supplies.

72
Q

what is an electric current

A

a flow of charge

73
Q

electrons flow through all metals , so metals are

A

conductors of electricity

74
Q

voltage (V) =

V =

A

current (A) x resistance (ohms)

I x R

75
Q

what usually happens in a conductor

A

the electrons are free to move between the atoms. the number of electrons flowing in any one direction is equal to the number of electrons flowing in any other direction.

76
Q

what happens in a conductor when a cell or battery is connected across a conductor

A

the electrons start flowing away from the negative terminal and to the positive terminal. now there is a net flow of charges or electric current.

77
Q

how do you measure current

A

using an ammeter

78
Q

the size of an electric current indicates…

A

the rate at which the charge flows

79
Q

if there is a current of 1A then it means

A

1C of charge is passing along the wire each second

80
Q

charge (C) =

Q =

A

current (A) x time (s)

I x t

81
Q

what is a volt

A

a joule per coulomb

82
Q

energy (j) =

A

charge (c) x voltage (v)

Q x V

83
Q

how do you measure volts

A

using a voltmeter

84
Q

series circuit

A

only one path the current can take

85
Q

parallel circuit

A

multiple paths and junctions that the current can take

86
Q

if one bulb in a series breaks,

A

it causes a gap int he circuit and all of the other bulbs will stop working

87
Q

the energy in a series circuit is shared between all the bulbs, so the more bulbs you add,

A

the dimmer they all become

88
Q

if one bulb in parallel breaks,

A

only bulbs in the same branch of the circuit break so not all of the bulbs will break

89
Q

in a series circuit how is the current distributed

A

the current is the same in all parts and not used up

90
Q

in a parallel circuit how is the current distributed

A

the current will be different in different parts of the circuit,

91
Q

voltage (V) =

V =

A

current (A) x resistance (ohms)

I x R

92
Q

practical: how to investigate how current varies with voltage with different components

A

have a circuit with a switch, variable resistor , voltmeter, ammeter and piece of wire. turn up the variable resistor to maximum and close the switch to take readings from the. ammeter and voltmeter. alter value of variable resistor or and take a new reading. repeat at least six times and plot values, drawing a graph of current against voltage

93
Q

on a current vs voltage graph what does a flat slope indicate

A

a high resistance

94
Q

what does a fixed resistor do

A

to control the sizes of currents and voltages. without it the voltage across the bulb may cause too large a current and the bulb will break

95
Q

how is a variable resistor different to a fixed resistor

A

you can vary the resistor, allowing the bulb to shine more brightly or less brightly.

96
Q

what is a thermistor

A

a resistor whose resistance changes quite.a lot even with small changes in temperature

97
Q

what is a light dependent resistor

A

it has a resistance that changes when light is shone on it. in the dark its resistance is high

98
Q

where are thermistors used

A

temp sensitive circuits like fire alarms

99
Q

where are LDRs used

A

automatic lighting controls and burglar alarms

100
Q

what are diodes

A

special resistors that allow charges to follow through them in one direction.

101
Q

when diodes are used in rectifier circuits what do they do

A

they convert alternating current into direct current

102
Q

PRACTICAL: investigate the motion of everyday objects (such as toy cars)

A
  1. Attach the bench pulley to the end of a long bench.
  2. Secure the mass hanger to one end of the string and attach the other to the toy car
    - pass the string over the bench pulley, and pull the car back so that the mass
    hanger is just resting on the floor.
  3. Mark the car’s position with masking tape - this is the end marker.
  4. Pull the car back so the mass hanger is raised and touches the pulley - mark the
    car’s position with tape - this is the starting marker.
  5. Use the tape measure to record the distance between the start and end markers.
  6. Release the car from the start marker and start the stop clock - stop timing when
    the car reaches the end marker (this will be the same time that the mass hanger
    reaches the ground).
  7. Repeat the experiment 5 times and calculate an average time.
103
Q

PRACTICAL: investigate how extension varies with applied force

A
  1. Using the ruler, measure the initial length of the first spring when no force is applied.
  2. Set up the spring so it is hanging securely from the clamp stand.
    ○ You can also secure the ruler to the clamp stand to ensure it does not move at all
    during the experiment.
  3. Add one of the masses to the end of the spring and record the extension of the spring.
    ○ The extension is the difference between the new length and the initial length.
  4. Continue adding masses and recording the extension each time.
  5. Plot a graph of force applied against the extension of the spring.
    ○ Force can be calculated from mass x gravitational field strength (i.e. 10 x the mass
    hanging on the spring).
    ○ The gradient of the line of best fit will be the spring constant as . k = F/x
    F
  6. Using this value, you can calculate the work done each time the spring extends
    ○ Use the formula . W = 1/2kx squared
104
Q

explain why a vehicles stopping distance is different to its breaking distance

A

stopping distances take into account the driver’s thinking distance as well as the vehicles breaking distance

105
Q

car safety features are designed to…

A

increase the time taken for a passenger’s momentum to change

106
Q

unbalanced forces acting on object makes them…

A

accelerate or decelerate

107
Q

what is a pivot

A

the fixed point where the turning effect of an object takes place.

108
Q

moment of a force =

A

force x perpendicular distance from pivot

F x d

109
Q

what are moments measured in

A

newton metrees (Nm)

110
Q

sum of anticlockwise moments =

A

sum of clockwise moments (if in balance)

111
Q

what is the centre of gravity/mass

A

it is the point at which the whole weight of the object appears to act. if we support the object at this point there is no turning moment in any direction about the point and it balances.

112
Q

what happens when an object is pivoted at the centre of gravity

A

there is no turning point

113
Q

what happens when an object is not pivoted at the centre of gravity

A

there is a turning point

114
Q

if the weight is closer to one end of a beam where will the most force be

A

on that end of the beam.

115
Q

momentum =

p =

A

mass x velocity

m x v

116
Q

what is momentum measured in

A

kg m/s

117
Q

when an unbalances force acts on an object

A

it causes a change in the momentum of that object

118
Q

inital momentum is

A

mu

119
Q

final momentum is

A

mv

120
Q

rate of increase of momentum is

F is

A

time

t

121
Q

momentum before a collision =

A

momentum after a collision

122
Q

what is the conservation of momentum principle

A

momentum before = momentum after

123
Q

why do cars have safety features

A

they increase the time over which the car’s momentum changes in an accident. they protect the passengers in case of an accident.

124
Q

what are crumple zones/what do they do

A

in a car, they collapse during a collision and increse the time during which the car is decelerating. they protect the passengers in case of an accident.

125
Q

newtons third law

A

when you push something it pushes you back just as hard but in the opposite direction. for every action there is an equal and opposite reaction.

126
Q

balanced forces act in

A

opposite directions on the same object

127
Q

action and reaction forces act in

A

opposite directions but always on different objects

edexcel igcse physics (13 decks)

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