AQA GCSE Combined Science Physics - Paper 2

Vector quantities

have magnitude and direction

Examples of vector quantities

force, velocity, momentum, acceleration

Scalar quantities

Only have magnitude

Examples of scalar quantities

speed, distance, time

Vectors

• Represented by an arrow

• 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

contact force

when two objects are touching for the force to act

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?

• Amount of matter an object is made of

• Same value everywhere

• Measured using a mass balance

What is weight?

• The force acting on an object due to gravity

• depends on the strength of the gravitational field at the location of the object

• Measured using newtonmeter

What is weight directly proportional to?

mass

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

What is 1J equal to?

1Nm

If all the forces acting on an object combine to give a resultant force of zero then the object is in ?

equilibrium

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

Extension is directly proportional to? (Hooke's Law)

The force applied

F∝e

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

What is displacement?

• 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

typical speeds

typical speed of a person walking

1.5m/s

typical speed of a person running

3m/s

Typical speed of a person cycling

6m/s

what is the typical speed of a car

25m/s

Typical speed of a train

55m/s

Typical speed of a plane

250m/s

What factors affect speed?

Fitness of the person

Age of the person

Distance travelled

Terrain

Climate

Gender of the person

What factors affect wind speed?

Temperature

Atmospheric pressure

Any large buildings or structures nearby e.g. forests reduce wind speed travelling through them

Acceleration

change in velocity in a certain amount of time

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

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?

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?

Inertia

Newton's First Law - Law of Inertia

Resultant force on a stationary object = 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

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.

Investigating acceleration

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

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

3) Alcohol

4) Drugs

5) Sleep deprivation

6) Distractions

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?

• More ekinetic energy

• More work needs to be done to stop it

• Greater braking force will be needed to make the vehicle stop within a certain distance

• Deceleration will be larger

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

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

What is the conservation of momentum?

In a closed system, the total momentum before an event is the same as after the event

Wave

something that transfers energy from one place to another

transverse waves

The vibrations are perpendicular (at right angles) to the direction of energy transfer

- direction of energy transfer is sideways - but oscillations are up and down

examples of transverse waves

- electromagnetic waves e.g light

- Ripples and waves in water

longitudinal waves

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 denser so it changes direction

Compression

regions where the air particles are very close together

Rarefaction

regions where the air particles are spaced out

amplitude

The amplitude of a wave is the greatest distance a point on the wave moves from its undisturbed postion

wavelength

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

frequency

the number of waves passing a point each second

1 Hz = 1 wave per second

period

time (in seconds) for one wave to pass a point

What is the speed of sound in air?

330m/s

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 transmitted through the material - carries on travelling

- The wave is absorbed by the material

- The wave is reflected - '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

1m-10⁴m

Length of a microwave

10⁻²m

Length of a infrared wave

10⁻⁵m

Length of a visible light wave

10⁻⁷m

Length of an ultraviolet wave

10⁻⁸m

Length of an x-ray

10⁻¹⁰m

Length of a gamma ray

10⁻¹⁵m

EM continuous spectrum

1) Radio waves

2) Microwaves

3) Infrared waves

4) Visible light rays

5) Ultraviolet waves

6) X-rays

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

ray diagrams

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