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physics paper 2 gcse aqa > forces > Flashcards

forces Flashcards

1
Q

examples of scalar quantities

A

mass, temperature,speed, energy, distance, time

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2
Q

scalar quantities

A

have a magnitude but no direction

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3
Q

vector quantities

A

-displacement
-weight
force
-acceleration
velocity
momentum

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4
Q

vector quantities

A

-have both direction and magnitude[

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5
Q

vectors can be presented using arrows

A

length of arrow represents magnitude of the vector

direction of arrow represents direction of the vector

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6
Q

definition of a force

A

a force is a push or a pull acting on an object due to the interaction with another object
all forces have both magnitude and direction- its a vector quantity
unit newtons

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7
Q

in contact forces, the two objects are

A

physically touching

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8
Q

contact forces:

A
  • tension
  • friction ( eg acts between water or aeroplane causing aeroplane to slow down and stop)
  • air resistance
  • normal contact force (an object on a table, object exerts downwards force on the table and that force is the weight of the lamp at the same time table exerts upwards force on the lamp) this can only happen if two objects are in direct contact
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9
Q

non contact forces two objects physically separated

A
  • gravitational force (attracts moon to Earth and Earth to moon
  • electrostatic force (force between two charged objects) objects with opposite charges experience a electrostatic force of attraction. objects with two like charges experience a electrostatic force of repulsion
  • magnetic force (force experienced by certain objects in a magnetic field)
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10
Q

gravity defintion

A

force of attraction between all objects

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11
Q

is gravity a contact or non contact force

A

a non contact force because two objects are physically separated

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12
Q

is gravity a scalar or vector quantity

A

is a vector quantity because it has magnitude and direction

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13
Q

definition of mass

A

mass tells us how much matter is in an object
unit is kilogram
scalar quantity because it does not have direction

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14
Q

key point about mass

A

mass of an object does not depend on where the object is

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15
Q

weight of an object is the force acting on it due to gravity

unit=newtons

A

weight of an object does depend on where it is

weight depends on gravitational field strength

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16
Q

what is gravitational field strength

A

measure of the force of gravity in a particular location

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17
Q

equation to calculate weight

A

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

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18
Q

weight of an object is directly proportional to mass

A

if we double the mass weight also doubles

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19
Q

a newton meter can be used to determine

A

the weight of an object

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20
Q

centre of mass

A

weight of an object(force acting on an object due to gravity) can be considered to act at a single point

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21
Q

definition of force

A

a force is a push or a pull acting on an object due to its interaction with another object
forces are vector quantities because they have both magnitude and direction

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22
Q

resultant force definition

A

single force that has the same effect of all the original forces acting together

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23
Q

how to calculate resultant force

A

subtract smaller force from larger force

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24
Q

what does it mean if the resultant force is 0N

A

the forces acting on the object are balanced

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25
Q

what does altitude mean

A

height above the ground

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26
Q

description of free body diagram of aeroplane

A

aeroplane is represented as a circle
the weight of the aeroplane is acting downwards towards the Earth
lift acting upwards
forward force provided by engine called thrust acting to the right
air resistance drag acting in reverse to thrust

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27
Q

Equation of work done

A

work done J= force N x distance M

distance must be in the line of action of the force

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28
Q

what is work done

A

work done is when a force is used to move an object

work done is an example of energy transfer

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29
Q

list elastic materials

A
  • slinky
  • rubber bands
  • rubber gloves
  • eraser
  • playground surface
  • tennis ball
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30
Q

in an elastic material

A

the stretching forces are equal in magnitude but opposite in direction
these forces cause the objects to stretch but when the forces are released, the object returns back to its orginal length

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31
Q

elastic materials will always return to their original length or shape if we take away forces acting on them

A

if we apply squeezing forces to the object the object compresses. if we take away the forces, the object returns to its original length
if we remove the forces acting on the material it recovers its orginal properties and returns to its orginal shape or length

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32
Q

elastic deformation

A

when we take away the forces acting on the object, the object will return to its original shape and length

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33
Q

how do we change an objects length or shape

A

we have to apply more than one force

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34
Q

what would happen if we only applied one force to a stationary object

A

forces are no longer balanced

the object would simply move rather than changing length or shape

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35
Q

when we stretch inelastic materials what happens

A

they do not return to their original shape or length when the forces are removed

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36
Q

example of inelastic materials

A

-certain polymers

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37
Q

force= spring constant n/m x extension m

A

force= spring constant n/m x extension

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38
Q

calculate the force required to extend a spring by 0,4 metres the spring constant is 200n/m

A

0.4 x 200= 8N

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39
Q

the same equation can be used to calculate compression how?

A

force (N)= k x e

e is compression in this case

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40
Q

when we stretch or compress an elastic object we are using a force to

A 
do work (transfer energy)
elastic potential energy is stored in the object
work done= elastic potential energy but that is only true if object is not inelastically deformed
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41
Q

an elastic material returns to its orginal shape when forces are removed
an inelastic material….

A

an inelastic material does not return to its original shape when forces are removed

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42
Q

When a person stretches or compresses an elastic object, ———– energy stores in the person’s
muscles transfer to the ———— energy store in the elastic object. This is an example of work
done. The total work done is ——— the energy transferred as long as the object is not inelastically deformed.

A

when a person stretches or compresses an elastic object, chemical energy stores in the person’s muscles transfer to the elastic potential energy store in the elastic object. this is an example of work done. the total work done is equal to the energy transferred as long as the object is not inelastically deformed.

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43
Q

what is the definition of elastic potential energy

A

energy stored in an elastic material when its stretched

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44
Q

energy used in stretching or compressing a material is stored as…

A

elastic potential energy

45
Q

what does hookes law state

A

if you apply a force in the form of a weight, to a spring it will stretch and the extension produced is directly proportional to force applied

46
Q

what is the limit of proportionality

A

the force applied is no longer directly proportional to the extension

47
Q

what equation is used to calculate pressure

A

pressure (pa)= force normal to surface (N) / area of surface m^2

48
Q

A gas inside a container applies a force of 40,000 N the wall of the container have an area of 8m^2 calculate pressure of the gas

A

40,000/ 8

50,000 Pa

49
Q

how does atmpspheric pressure dcrease with an icnrease in height

A

atmosphere is a thin layer of air around the Earth
the atmosphere is most dense at the surface of the Earth
at the Earth’s surface there is the greates number of particles for a given volume
atmosphere gets less dense as we increase altitude
pressure of atmosphere is caused by air molecules colliding with a surface
as a surface increases height above ground level, number of air molecules above surface decreases
this means that atmospheric pressure decreases with an increase in height

50
Q

why do mountain climbers need an oxygen supply

A

air pressure on mountain may be too low to supply all oxygen they need

51
Q

crips packet inflates because

A

at ground level, pressure inside the bag is equal to pressure outside the bag however when aeroplanes are flying the air pressure in the cabin is kept at slightly lower pressure than air pressure on the ground. air pressure inside the bag is now greater than the air pressure inside the cabin

52
Q

as surface height above ground level increases

A

number or air molecules above the atmospehere decreases so atmospeheric pressure ddecreases with an increase in height
atmosphere gets less dense as we increase altitude

53
Q

what os pressure of the atmosphere caused by

A

air molecules colliding with a surface

54
Q

How do particles in fluids produce pressure on walls of the container

A

When particles in a fluid collide with the walls of the container, they exert a force. This force acts at
right angles to the surface of the wall. Scientists call this a normal force (ie acting at right angles).

55
Q

How do particles in fluids produce pressure on walls of the container

A

When particles in a fluid collide with the walls of the container, they exert a force. This force acts at
right angles to the surface of the wall. Scientists call this a normal force (ie acting at right angles).

56
Q

pressure of column of liquid equation

A

pressure (pa)= height of column (m)- denisty of liquid kg/m^3 x gravitational field strength N/kg

57
Q

the pressure increases with the height of the column ( the depth) because

A

as the depth increases, there is a greater weight of liquid acting downwards
pressure of liquid also increases with density
liquids with a greater density have a greater weight acting downwards

58
Q

the pressure of a liquid depends on teh depth because the greater teh depth teh greater the weight acts downwards

A

as pressure increases there is a greater weight of liquid acting downwards

59
Q

the pressure of q liquid dpeends on teh depth

the bottom of the liquid

A

is a at a greater depth than at the top of the liquid
the bottom of the liquid experiences a larger pressure than at the top
because of this there is a larger force acting at the bottom of the object
there is a resultant force acting upwards

60
Q

what is upthrust

A

the resultant force acting upwards

61
Q

for an object to float

A

upthrust must be equal to objects weight ( force acting downwards due to gravity)

62
Q

if the upthrust is less than teh objects weight then the

A

object sinks

63
Q

when an object is lowered the level of water rises why

A

because the object displaces the water

64
Q

the size of the upthrust acting on an object is the same as the weight of the water displaced by the object

A

the size of the upthrust acting on an object is teh same as the wieght of the water displaced by the object
if an object can displace its own weight of water, then the upthrust will equal teh objects weight and the object will float

65
Q

an object that is less dense only needs to displace a small volume of water before the weight of the water displaced equals the wieght of the object now the upthrust is euqal to teh wieght of the objecr and the objetc can float. in this cas ethe object floats high in the water

A
66
Q

an object that is more dense than water

A

object cannot displace water equal to its own weight

the weight of the object is greater than uothrust so the object sinks

67
Q

why does a greater depth have a greater pressure

A

because bottom of teh object is at ta greater depth then at the top so it experiences a greater pressure. this means the the bottom of the object experiences a greater force than atthe top.
because of this we have a resultant force acting upwards and scientists call this upwards force upthrust an object will float if the upthrust is equal to the weight of the object if the weight is greater than the upthrust then the object will sink.

68
Q

momentum

A

all moving objects have a momentum

69
Q

if an object is not moving the momentum is always

A

zero

70
Q

momentum equation

A

momentum kg/ms= mass kg x velocity m/s

71
Q

conservation of momentum

A

in a closed system, total momentum before an event is equal to total momentum after event

72
Q

conservation of momentum question: a van with a mass of 1400kg is travelling at 20m/s. the van collides with a stationary car with a mass of 1000 kg. both the van and the car continue moving together. calculate velocity of van and car together

A

1400x20=28000kgm/s
car has momentum of zero because its stationary
total momentum after collision =28,000kgm/s
to calculate velocity divide total momentum by mass of the car
28000/2400=
11.67m/s

73
Q

rapid changes in momentum can be extremely dangerous

A

a huge force is placed on the passenger and this could increase the risk of injury

74
Q

force(N)= mass (kg) x acceleration m/s^2

equation for acceleration

A

change in velocity/ time

75
Q

combine the two equations to calculate force

A

force= mass x change in velocity/ change in time

76
Q

how do you calculate change in momentum

A

mass x change in velocity

77
Q

a man with a mass of 100kg is a passenger in the car. the car is travelling at 30m/s. the car comes to a stop in 1 s. calculate forces acting on the man

A

100x30/1 force= mass x change in velocity/ change in time

3000N

78
Q

a force acting on a person could be fatal

rapid changes in momentum lead to huge forces applying and these are extremely dangerous

A

a force acting on a person could be fatal rapid changes in momentum lead to huge forces applying and tehse are extremly dangerous

79
Q

how can we reduce danger

A

make change in momentum over a longer itme

80
Q

devices that can slow down momentum change

A
  • air bags
  • safety belt
  • helmet
  • cushioned surface
  • crashmat
81
Q

how do these reduce momentum change

A

they reduce the forces acting and reduces risk of serious injury

82
Q

when momentum is acting in a backwards direction

we present velocity ….

A

with a negative sign because velocity and momentum are vector quantities they have both magnitude and direction

83
Q

atmospheric pressure decreases with height

explanation

A

the atmosphere is a layer of thin air that surrounds the Earth. atmospheric pressure is created on a surface by air molecules colliding with the surface
as the altitude (height above the ground increases) atmospheric pressure decreases because as altitude increases atmosphere gets less dense fewer air molecules that are able to collide with the surface
there are also fewer air molecules above a surface as height increases. this means that teh weight of the air above it whivh contributes to atmospheric pressure, decreases with altitude

84
Q

the more dense a given liquid, the more particles it has in a certain space this means that

A

there are more particles able to collide so pressure is higher
as the depth of the liquid increases, number of particles above that [point increases the weight of these particles adds to pressure felt at that point so liquid pressure increases with depth.
p=hpg

85
Q

stopping distance

A

total distance travelled from when driver spots obstruction to when the car actually stops

86
Q

the stopping distance can be divided into two parts
the thinking distance
braking distance

A

thinking distance- distance travelled by car during drivers reaction time
reaction time- time taken for driver spot the obstruction, make a decision and move their foot to the brake

87
Q

the braking distance is the distance

A

car travels from when driver applies breaks to when car actually stops

88
Q

greater the speed of the vehicle

A

greater stopping distance assuming same force was applied to breaks

89
Q

reaction time varies from

A

0.2 to 0.9 seconds

reaction time can be measured using ruler

90
Q

how do we measure reaction time

A

one person holds the ruler and a volunteer places their fingers on either side. the ruler is dropped and the volunteer has to catch it
the further the ruler falls before its caught the longer the reaction time
by measuring distance the ruler fell we can look up reaction time in a table

91
Q

should a driver have a short reaction time or a long reaction time

A

drivers should have shortest possible reaction time so that they can react very quickly when they see obstructions.

92
Q

what factors affect the braking distance ( distance travelled when drivers apply brakes to when drivers actually stop)

A

terrain
wet or icy conditions reduce friction between tyres and the road and increase braking distance.
braking distance will also increase if car has worn out tyres because it reduces friction between tyre and road.
worn brakes also increase breaking distance

93
Q

what factors would affect reaction time thus thinking distance

A

-tiredness a tired driver would have a longer reaction time
-alcohol and drugs can make the reaction time longer
-distractions in the car such as a mobile phone will also increase drivers reaction time.
because these factors increase reaction time they also increase thinking distance

94
Q

what happens if a car has a greater speed

A

the stopping distance will increase larger force will be needed to stop the car

95
Q

what are ideal conditions like

A

driver is well rested
no alcohol or drugs
weather is good no fog mist , sunny weather
road condtions are normal no wet icy terrain

96
Q

recap stopping distance of a car consists of thinking distance + braking distance
defintions for all trhee

A

stopping distance- sum of thinking and braking distance. distance car travels from when driver spots obstruction to when vehicle actually stops
braking distance- distance travelled by car from when driver applies breaks to when car actually stops.
thinking distance- distance travelled by car during reaction time. reaction time varies from 0.2 to 0.9 seconds. we can measure it using a ruler. reaction time is the time taken to spot obstruction, make a decision and move foot to brakes.

97
Q

any moving object has kinetic energy

A

1/2mv^2

kinetic energy dpeends on velocity squared if we double velocity kinetic energy of car quadruples

98
Q

when a car brakes and comes to a stop

what is all the kinetic energy converted to

A

other forms of energy

99
Q

what happens during braking

A

brake presses against wheel
force of friction now acts between brake and the wheel
kinetic energy of teh car is conevrted to thermal energy in the brakes
this causes temperature of the brakes to increase
at the same time, car slows down as it loses kinetic energy
the greater the speed, the greater the breaking force needed to stop the car in a certain distance.
if a car is travelling at high speeds. the driver needs to brake
they have to apply a very large breaking force
a large breaking force will cause the car to decelrate rapidly
a large amount of kinetic energy is transferred to thermal energy in the brakes
this can cuase brakes to overheat and driver could lose control of vehicle

100
Q

force mass acceleration

A

force- mass x accerlation

101
Q

‘if a car is travelling at high speeds the driver needs to brake then they have to apply a very large breaking force

A

a large breaking force cuases car to decelerate rapidly at the same time,a large amount of kinetic energy is transferred to thermal energy in the brakes
this can cause brakes to overheat and driver can lose control of vehicle

102
Q

a car of 1000kg is travelling at speed of 3m/s on the motorway they decerlate to leave the motorway velocity decreases to 0 in ten seconds

A

force- mass x acceleration

1000x30= 3000N

103
Q

typical speeds
walking
runnning
cycling

A

walking 1.5m/s
running 3m/s
cycling 6m/s

104
Q

speed can depend on terrain and nature of person

A

an older unfit person will have a slower speed than a fit young person
people move more rapidly on flat ground than on hill
speed can also depend on distance travelled

105
Q

typical vehicle speeds

A

car on a main road 13m/s
fast train 50m/s
cruising aeroplane 250m/s

106
Q

speed of sound in air

A

330 m/s
sound travels faster on warmer days than cooler ones
speed of a moving object is not constant

107
Q

objects moving in a circle- velocity

A

if an object moves at constant speed in a circle, its velocity is constnatly changing even though its speed is constant that is because velocity is speed in a given direction

108
Q

forces acting on skydiver

A

as soon as a skydiver jumps out of the plane the only force acting is weight
this is due to gravity
it will not change during a journey
becayse of weight skydiver experiences a resultant force acting downwards so they accelerate towards the ground
as the skydiver falls, they expereince friction with air molecules ( this is called air reistsance and it acts upwards)
the weight is greater than the air resistance so the skydiver accelerates downwards
as the sky divers velocity increases the air reistance also increases
at a certain point the air reistsance balances the weight
now there is no resultant force so velocity stays constant
skydiver has reached terminal velocity
this velocity is extremely great, the sky diver would die if they touched the ground
so the skudiver opens their parachute increasing their surface area this causes air resistance to massively increase
air resistance is greater than the weight
so there is a resultant force acting upwards
this causes skydiver to decelerate (velocity decreases)
because velocity has decreased air resistance also decreases
at some point air resistance balances teh weight and teh resultant force will be 0.
so vlocity will stay constant
skydiver is falling at a lower terminal velocity
this is now safe for them to hit the ground

109
Q

velocity time graph

A

as soon as sky diver jumps out of the plane only force acting is weight
skydiver accelerates towards teh ground
as the skydiver falls air resistance increases
but weight is still greater than air resistance so teh sky diver ocntinues to accelerate
velocity increases, air resistance also increases
air resistance balances weight and resultant force is zero so velocity stays constant
terminal velocity
this velocity is extremely great the sky diver would die if they hit the ground
at this point skudiver opens parachute
this massively increases surface area and the air resistance increases massively
air resistance is now greater than the weight
so the resultant force now acts upwards
vecause resultant force acts upwards skydiver decelerates
they are still moving towards the ground but at much lower velocity
because velocity has decreased, air resistance has also decreased
when air reistance balances the weight resultnat force is now zero
velocity is now constant and this is alower terminal velocity
tje sky diver lands

physics paper 2 gcse aqa (4 decks)

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