AQA GCSE Combined Science Physics - Paper 2
Terms in this set (146)
have magnitude and direction
Examples of vector quantities
force, velocity, momentum, acceleration
Only have magnitude and no direction
Examples of scalar quantities
speed, distance, time
represented by an arrow - the length of the arrow shows the magnitude. The direction of the arrow shows the direction of the quantity
A force is
a push or pull on an object that is caused by it interacting with something
when two objects are touching for the force to act, its a ....
examples of contact forces
friction, air resistance, tension in ropes. etc
If the objects do not need to be touching for the force to act, the force is a ......
non contact force
examples of non contact forces
magnetic force and gravitational force
Two effects of gravity
- makes all things fall towards the ground
- gives everything a weight
What is mass?
The amount of material an object is made of
It is the same value everywhere
Measured using a mass balance
What is weight?
The force acting on an object due to gravity
It depends on the strength of the gravitational field at the location of the object
Measured using a calibrated spring balance - newtonmeter
Equation for Weight
Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg)
What is weight directly proportional to?
What are free body diagrams?
Diagrams that show all the forces acting on an object
What is the resultant force?
The single force that replaces multiple forces acting at a single point
How is work done?
When a force moves an object through a distance, energy is transferred and work is done on the object
Equation for 'Work Done'
Work done (J) = Force (N) x Distance (m)
What is 1J equal to?
If all the forces acting on an object combine to give a resultant force of zero then the object is in ?
What could happen when you apply a force to an object?
It may stretch, compress or bend
What happens when an object is elastically deformed
The object can go back to its original shape and length after the force has been removed
What happens when an object is inelastically deformed?
The object won't return to its original shape and length after the force has been removed
Equation for Force 1
Force (N) = Spring Constant (N/m) x Extension (m)
Extension is directly proportional to? (Hooke's Law)
The force applied
What is the limit of proportionality?
The point at which extension is no longer directly proportional to force
Practical: Investigating the link between force and extension
- First, measure the original length of the spring using a milimetre ruler
- Next, add different masses on the spring and measure the length of the spring in each case.
- The extension = change in length
- Repeat this process until you have enough measurements ( no fewer than 6)
- Plot a graph with extension of the spring on the x axis and force on the y axis.
- The graph will only start to curve if you exceed the limit of proportionality
Equation for Elastic potential energy
Elastic potential energy (J) = 1/2 x Spring Constant (N/m) x extension^2 (m)
Ee = 1/2Ke^2
What is displacement?
It measures the distance and direction in a straight line from an object's starting point to its finishing point
What is velocity?
Speed (how fast you're going) in a given direction
Equation for Speed
Distance Travelled (m) = Speed (m/s) x Time (s)
typical speed of a person walking
typical speed of a person running
Typical speed of a person cycling
what is the typical speed of a car
Typical speed of a train
Typical speed of a plane
What factors affect speed?
Fitness of the person
Age of the person
Gender of the person
What factors affect wind speed?
Any large buildings or structures nearby e.g. forests reduce wind speed travelling through them
change in velocity in a certain amount of time
Equation for Acceleration
Acceleration (m/s²) = Change in Velocity (m/s) / Time (s)
What is deceleration?
Negative acceleration - when something slows down, the change in velocity is negative
What is constant acceleration?
Uniform acceleration - acceleration due to gravity is uniform for objects in free fall
Equation for Uniform Acceleration
Final velocity² (m/s) - Initial velocity² (m/s) = 2 x Acceleration (m/s²) x Distance (m)
Distance-Time Graphs - Features
1) Gradient = speed
2) Flat sections = object is stationary
3) Straight uphill sections = object is travelling at a steady speed
4) Curves = object is accelerating or decelerating
5) Steepening curve = object is speeding up
6) Levelling off curve = object is slowing down
Velocity-Time Graphs - Features
1) Gradient = acceleration
2) Flat sections = object is travelling at a steady speed
3) Uphill sections = object is accelerating
4) Downhill sections = object is decelerating
5) Curves = object is changing acceleration
The steeper the graph, the greater the acceleration or deceleration
What does friction do?
It causes objects to slow down when they rub against another surface
What is drag?
The resistance you get in a fluid
Air resistance is a type of drag
How do you reduce drag?
Keep the shape of an object streamlined
process of a falling object
1) When a falling object first sets off, the force of gravity is much more than the frictional force slowing it down, therefore the object accelerates
2) As the speed increases, the friction builds up
3) The acceleration is gradually reduced until eventually, the friction force is equal to the accelerating force - the resultant force is 0
4) At this point, it will have reached maximum speed or terminal velocity and will fall at a steady speed
What determines the terminal velocity?
The terminal velocity of any object is determined by its drag in comparison to its weight
In the last few metres of his descent during the parachute stage, the person travels at a terminal velocity. Explain why (2)
- Because the drag had the same force on the parachuter as the weight
- weight pushes him down
- Drag/air resisance keeps him. Hes reached terminal velocity (2)
What is the tendency for objects to continue at the same speed in the same direction called?
Newton's First Law - Law of Inertia
If the resultant force on a stationary object is zero, the object will remain stationary
If the resultant force on a moving object is zero, it will just carry on moving at the same velocity
Newton's Second Law
Force ∝ Acceleration
Acceleration is inversely proportional to the mass of an object
Equation for resultant force
Resultant Force (N) = mass (Kg) x acceleration (M/s^2)
Newtons third Law
When two objects interact, the forces they exert on each other are equal and opposite
An action always has an equal and opposite reaction
Explain why you don't move when you lean on a wall, even though you are exerting a force (3)
When you lean on a wall, you exert a force on the wall. Due to Newtons third Law, the wall also exerts an equal but opposite force back onto you.(1) You also exert a force on the ground and the ground exerts a force on you(1)The resultant force is zero, so you remain stationary (1)
Investigating effect of mass
Add masses to the trolley one at a time to increase the mass of the system
2)Record average acceleration for each mass
To reduce the effect of friction use an air track.
1) Set up a trolley so it holds a piece of card that will interrupt the signal on the light gate twice.
2) This will measure acceleration.
3) Using a light measure the first and second point it passes.
Work out an average acceleration.
To reduce the effect of friction use an air track.
investigating effect of force
1) Keep total mass of the system the same but the change the mass on hook
2) Start with all the masses onto trolley
3) Transfer the hooks one at a time to the hook, to increase the accelerating force
4) The mass of the system stays the same as you're transferring the masses from one part of the system to another (the hook)
5) Record the average acceleration for each force
To reduce the effect of friction use an air track.
What is the thinking distance?
How far the car travels during the driver's reaction time
What is the braking distance?
The distance taken to stop under the braking force
What is stopping distance?
The distance it takes for a car to stop in an emergency
Equation for Stopping Distance
Stopping Distance = Thinking Distance + Braking Distance
What is thinking distance affected by?
1) Speed - the faster you're going, the further you'll travel during your reaction time
2) Your reaction time - the longer it is, the longer your thinking distance
5) Sleep deprivation
What is braking distance affected by?
1) Speed - the faster a vehicle travels, the longer it takes to stop
2) Weather/Road surface - if it's wet or icy, there is less grip (and less friction) between a vehicle's tyres and the road, which can cause tyres to skid
3) Condition of tyres - if the tyres are bald, then they cannot get rid of water in wet conditions, thus leading to skidding on top of the water
4) Quality of brakes - if brakes are worn or faulty, they won't be able to apply as much force as well-maintained brakes, which could be dangerous when wanting to brake hard
What happens when a vehicle is going really fast?
It has more energy in its kinetic energy stores, so the more work needs to be done to stop it - a greater braking force will be needed to make the vehicle stop within a certain distance, therefore the deceleration will be larger
The larger the deceleration, the more dangerous it will be as the brakes could overheat or cause the vehicle to skid
At one time in the investigation, the cyclist was distracted.
The distraction increased the stopping distance of the bike but did not affect the braking distance
Explain why the stopping distance increased
The cyclist's reaction time increased (1)
The thinking distance increased (1)
Stopping distance is thinking distance plus braking distance (1)
Describe how Newtons third law applies to the forces between the bike and the trailer
The forces of the bike on the trailer and the trailer on the bike are equal in size and opposite in direction
Typical reaction time
in between 0.2 - 0.9
Measure reaction time :
- Ruler drop test
- Computer based experiments
Marks reaction time is tested using the ruler drop test. He is tested early in the afternoon and at night.
In the afternoon, he catches the ruler after it has fallen a distance of 16.2cm. At night, he catches the ruler after it has fallen 18.5cm.
a) Calculate Mark's reaction time in the afternoon. Give your answer to 2 significant figures
v^2 - u^2 = 2as
v^2 = 2 x 9.8 x 0.162 + 0 = 3.1752 (1)
v= √3.1752 = 1.781 m/s (1)
a = Δv/t
t = Δv / a
= 1.781 / 9.8 = 0.181 s (1)
= 0.18 (to s.f)
What is momentum?
How much 'oomph' an object has
All moving objects have it
The momentum of one thing is always equal to the momentum of another thing e.g. a skateboarder has the same momentum as the skateboard
Equation for Momentum
Momentum (kg m/s) = mass (kg) x velocity (m/s)
What is the conservation of momentum?
In a closed system, the total momentum before an event is the same as after the event
something that transfers energy from one place to another
The vibrations are perpendicular (at right angles) to the direction of energy transfer
- direction of energy transfer is sideways - but
are up and down
examples of transverse waves
- electromagnetic waves e.g light
- Ripples and waves in water
The oscillations are parallel to the direction of energy transfer
examples of longitudinal waves
sound waves e.g ultrasound
Explain the differences between the properties of the sound waves produced by the motor and the water waves in the ripple tank
Sound waves are longitudinal, in longitudinal waves the oscillations are parallel to the direction of energy transfer
Water waves are transverse. In transverse waves, the oscillations are perpendicular to the direction of energy transfer
Explain why the light is refracted
Because light travels more slowly (in the glass block than in the air) so it changes direction
regions where the air particles are very close together
regions where the air particles are spaced out
wave speed equation
wave speed (m/s) = frequency (H/z) x wavelength (m)
V = f λ
The amplitude of a wave is the greatest distance a point on the wave moves from its undisturbed postion
The wavelength of a wave is the distance from a point on one way to the equivalent point on the adjacent wave
measure wavelength on longitudinal waves
measure from one compression to the next compression or from one rarefaction to the next rarefaction
the number of waves passing a point each second
1 Hz = 1 wave per second
time (in seconds) for one wave to pass a point
equation for period
period = 1/frequency (H/z)
What is the speed of sound in air?
measuring the speed of water ripples practical
use signal generator attached to dipper of ripple tank - can create water waves at set frequency
use strobe light to see wave crests on a screen below the tank
increase frequency of strobe light until wave pattern on the screen appears to freeze and stop moving.
Distance between each shadow line is equal to one wavelength
Measure the distance between shadow lines that are 10 wavelength apart, then divide this distance by 10 to find the average wavelength
use V = f λ
strobe is effective because
it allows you to measure a still pattern instead of a constantly moving one
required practical: waves in a solid
- Turn on the signal generator and vibration transducer. String will start to vibrate
- Adjust the frequency of the signal generator until there's a clear wave on the string
- Measure the wavelength of these waves by measuring the lengths of 5 half wavelengths in one go, then divide to get the mean half wavelength, then double this to get a full wavelength
- Frequency of the wave is whatever the signal generator is set to
- use V = f λ to find the speed of the wave
3 things that could happen when a wave meets a boundary between two materials :
- The wave is
through the material - carries on travelling
- The wave is
by the material
- The wave is
- 'sent back' - this is how echoes are produced
Rule for all reflected waves
Angle of incidence = angle of reflection
What is the angle of incidence?
The angle between the incoming wave and the normal
What is the angle of reflection?
the angle between the refracted wave and the normal
What is the normal?
An imaginary line that's perpendicular to the surface at the point of incidence
Length of a radio wave
Length of a microwave
Length of a infrared wave
Length of a visible light wave
Length of an ultraviolet wave
Length of an x-ray
Length of a gamma ray
EM continuous spectrum
1) Radio waves
3) Infrared waves
4) Visible light rays
5) Ultraviolet waves
7) Gamma rays
mnemonic for EM spectrum
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on the red end of spectrum, waves have a
lower frequency, longer wavelength
on the violet end of the spectrum waves have a
higher frequency, shorter wavelength
What is refraction?
When a wave hits a boundary at angle it will change direction
What happens during refraction?
The wavelength of a wave changes but the frequency stays the same
What affects the rate of refraction?
How much the wave speeds up/slows down - this depends on the density of the two materials
If the wave slows down, it will bend towards the normal
If the wave speeds up, it will bend away from the normal
What is optical density?
A measure of how quickly light can travel through a material - the higher the optical density, the slower light waves travel through it
draw boundary between two materials
draw incident ray that meets the normal at boundary
angle between incident ray and normal = angle of incidence
now draw the refracted ray on other side of boundary
wave front diagrams
a wave front is a line showing all of the points on a wave that are in the same position as each other after a given number of wavelengths
Describe how radio waves can be produced
Produced by alternating currents/oscillations of charged particles in electrical circuits
Why are radio waves used
because they can travel long distances before being absorbed e.g by buildings and trees
State one use of radio waves
Hands free Bluetooth headsets to use in the car
- Used for communication to and from satellites because microwaves can pass through the atmosphere without being reflected or refracted
- Slight time delay between a signal being sent & received from a satellite due to the long distance it's had to travel
Microwaves - ovens - use a different wavelength from satellites
Microwaves need to be absorbed by the water molecules in food
The microwaves penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules - causes the water to heat up
The water molecules then transfer this energy to the rest of the food molecules by heating - quickly cooks the food
- Given out by all objects, hotter the object, the more IR radiation it emits
- Infrared cameras used to detect infrared radiation and monitor temperature. The hotter an object is, the brighter it appears
- Food can be cooked using IR radiation - temperature of food increases when it absorbs IR radiation
optical fibres are
thin glass or plastic fibres that can carry data over long distances as pulses of visible light
- used to carry telephone and cable t.v signals
Used in tanning - tanning salons where UV lamps are used to give artificial suntans.
Overexposure to UV radiation = dangerous - increases risk of skin cancer and causes premature ageing.
X-rays and Gamma rays
Both used for medical imaging - x-rays can be used to visualise broken bones, Gamma rays are used to detect cancers
Both X-rays and Gamma rays are very penetrative - can easily pass through body tissue
X-rays are absorbed by bones which is why we can see them on X-ray images
State two uses of X-rays
X-ray photographs (1)
Treating cancers (radiotherapy) (1)
Explain why plastic optical fibres use pulses of visible light to transmit data
Visible light is easy to refract to the angles that are needed to trap the light ray inside the optical fibre (1) Visible light is also not easily absorbed or scattered in a fibre (1)
Infrared radiation: Leslie cube practical
Leslie cube is a hollow, watertight metal cube with four different surfaces ; matt black, white, shiny black, shiny metallic
- First, fill the Leslie's cube with hot water
- Then point an infrared detector at each of the four surfaces and record the amount of infrared emitted
- Keep the same distance between Leslie's cube and the infrared detector so measurements are repeatable
- Results = matt black emits the most infrared radiation, followed by shiny black, then white, then shiny metallic = emits least IR radiation
Infrared radiation: Absorption: Melting wax practical
- Bunsen burner with two metal plates on either side. one plate is painted shiny metallic, and the other is painted matt black.
- On other side of plates, vaseline is used to attatch a drawing pin
- Switch on the heater and start timing, record the time it takes for the vaseline to melt and the drawing pins to fall off
- The drawing pin falls of the matt black plate first because matt black absorbs more IR than shiny metallic surfaces
- IR tends to be reflected from shiny metallic surfaces
Dangers of EM waves
Low frequency e.g radio waves = not harmful - pass through soft tissue without being absorbed
High frequency e.g gamma rays transfer lots of energy = lots of damage
X- rays + Gamma rays = ionising radiation = gene mutation/cell destruction, and cancer
- Radiation Dose = measured in
= measure risk of harm from body being exposed to radiation
Permanent and Induced Magnets
permanent magnets = produce their own magnetic fields
induced magnets = an object that becomes a magnet when placed in a magnetic field
What is a magnetic field?
A region where other magnets or magnetic materials experience a non contact force
The stronger the magnetic field...
...The closer together the magnetic field lines are
Where is the magnetic field strongest?
At the poles of the magnet
Two of the same poles =
Two different poles =
Repulsion of each other
Attraction to each other
What do compasses do?
They show the direction of magnetic fields - they contain a tiny bar magnet whose north pole is attracted to the south pole of any other magnet it is near
What happens when a current flows through a wire?
a magnetic field is produced around the wire
The larger the current, the ...
larger the magnetic field
The magnetic field is ? closer to the wire, as we move further from the wire, the strength of the magnetic field ?
How do you work out the direction of the magnetic field produced by a wire
use right hand grip rule -
use your right hand and point your thumb in the direction of current and curl your fingers
The direction of your fingers = direction of field
How do you increase the strength of a magnetic field?
By wrapping the wire into a coil called a solenoid. When the current is turned on , there is a strong and uniform magnetic field inside the solenoid
3 ways to increase the magnetic field produced by a solenoid
- Increase the current
- Increase the number of coils in the wire
- Place a piece of Iron inside the solenoid (iron core)
A solenoid with an iron core is called an ?
Electromagnets are extremely useful as ?
you can change the strength of the magnetic field by changing the size of current and you can turn the electromagnet on or off
What is the motor effect?
When a current-carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet & the conductor to exert a force on each other - this can cause the wire to move
What does the force acting on a conductor in a magnetic field depend on?
1) The magnetic flux density
2) The size of the current through the conductor
3) The length of the conductor that's in the magnetic field
Flemings left hand rule
Used to find the direction of a force
1) Use your left hand and point your First Finger in the direction of the Field
2) Point your seCond finger in the direction of the Current
3) Your thuMb will then point in the direction of the force (Motion
Forces act on the two side arms of a coil of wire that's carrying a current - the usual forces which act on any current in a magnetic field
Since one coil is on a spindle, it rotates as the forces act one up & one down
The split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction
The direction of the motor can be reversed by swapping the polarity of the dc supply (reversing the current) or swapping the magnetic poles over (reversing the field)