Full Physics Paper 2

SI unit - time

seconds(s)

SI unit - length

metre(m)

SI unit - current

ampere(A)

SI unit - amount of substance

mole(mol)

SI unit - mass

kilogram(kg)

SI unit - temperature

Kelvin(K)

giga

G, 10^9

mega

M 10^6

kilo

k, 10^3

centi

c, 10^-2

milli

m 10^-3

micro

μ 10^-6

nano

n 10^-9

How to convert celsius to Kelvin

C + 273.15 = K

how to convert from N/cm² to pascals

pascals is N/m² so multiply by 10000 (100×100)

systematic error

All data points are affected by the same amount. E.g. Scale has not been zeroed before use.

random error

Only some data points are affected, or all data points are affects by a different amount. E.g. taking measurement from a fluctuating scale or multimeter.

how can you improve accuracy in time measurements

Using a longer time to reduce percentage uncertainty due to human reaction time. E.g. time over longer distance or for multiple rotations.

Give ways in which measurements can be taken accurately.

Measure at eye level to reduce parallax error

Repeat and average

Use an instrument with a higher resolution

Increase time so that human reaction time is a smaller percentage of the measurement

Record with a slow motion camera with ruler and timer in shot.

Energy Store - Kinetic

the energy of a moving object

Energy Store - Gravitational

The energy an object has due to its height in a gravitational field

Energy Store - Elastic

the energy stored when an object is stretched, squashed or bent

Energy Store - Magnetic

the energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart

Energy Store - Electrostatic

the energy stored when repelling charges have been moved closer or when attracting charges have been pulled further apart

Energy Store - Chemical

the energy stored in chemical bonds, such as those between molecules

Energy Store - Nuclear

the energy stored in atomic nuclei when they release energy from their nuclear store during nuclear reactions

Energy Store - Thermal

the total kinetic and potential energy of the particles in an object, in most cases this is the vibrations - also known as the KE - of particles. in hotter objects, the particles have more thermal energy and vibrate faster

Energy transfer pathways

Mechanically

Electrically

By heating

By radiation

energy transfer - mechanical

When a force acts on an object (e.g. pulling, pushing, stretching, squashing)

energy transfer - electrical

A charge moving through a potential difference e.g charge flowing through an object

energy transfer - heating by particles

energy transfers from a hotter object to a cooler one e.g a fire burning an object

energy transfer - heating by radiation

Energy transferred by electromagnetic waves (e.g. visible light)

How do energy flow diagrams work?

Different labels represent the energy store at that point.

The arrows represent the energy transfer from one type of store to another.

How do Sankey diagrams work?

Arrows represent the types of energy transferred.

The ones that are straight are useful energy.

The ones that curve to the bottom are wasted energy.

The thickness of all the arrows correspond to a numerical value of the energy type in question.

The thickness of each arrow should be in proportion to each other.

system

an object or a group of objects

What happens when a system is in equilibrium?

Nothing changes, so overall nothing happens

3 states of a thermodynamic system

Closed

Open

Isolated

Open thermodynamic system

allows the exchange of energy and matter to or from its surroundings

Closed thermodynamic system

can exchange energy but not matter to or from its surroundings

Isolated thermodynamic system

does not allow the transfer of matter or energy to or from its surroundings

principle of energy conservation

energy cannot be created or destroyed, it can only be transferred from one store to another

useful energy transfers when a bat hits a ball

transfer from kinetic store of bat to kinetic store of ball

wasted energy transfers when a bat hits a ball

kinetic store of bat to:

thermal store of bat

thermal store of ball

thermal store of surroundings

useful energy transfers when boiling water in a kettle

energy transferred from the mains supply to the thermal store of the heating element in the kettle as as that gets hotter, energy is transferred to the thermal store of the water

wasted energy transfers when boiling water in a kettle

Some of the energy is transferred to the thermal store of the plastic kettle

And some energy is dissipated to the thermal store of the surroundings due to the air around the kettle being heated

How is energy transferred by heating in terms of particles

increase the energy in the kinetic store of the particles that make up that system, which increases the energy in the thermal store of the object

When is energy transferred by force

When mechanical work is done - when a force acts over a distance

How is energy transferred when a current flows?

Current is the flow of charge.

A current flows when there is a potential difference, supplied by a cell or power supply.

The power supply transfers energy electrically to components (electrical work is done).

Energy from the cell’s chemical store is transferred to the lamp’s thermal store, heating the filament.

The lamp transfers energy to the surroundings by heating and radiation (light).

Some energy is also transferred by heating to the wires due to resistance.

How is work done?

When an object is moved over a distance by a force acting in the direction of its displacement

work done equation

W = F x d

W = work done in joules

F = force in newtons

d = distance in metres

How do changes in height affect the GPE of an object?

If the object is lifted up then energy is transferred to its GP store

If the object falls then energy is transferred away from its GP store

gravitational potential energy equation

ΔGPE = mgΔh 

ΔGPE = change in gravitational potential energy, in joules (J)

m = mass, in kilograms (kg)

g = gravitational field strength in newtons per kilogram (N/kg)

Δh = change in vertical height in metres (m)

kinetic energy equation

KE = ½ mv²

KE = kinetic energy in joules (J)

m = mass of the object in kilograms (kg)

v = speed of the object in metres per second (m/s)

What is a perfect energy transfer and when can it assumed to be so?

a transfer such that there is no wasted energy

it can be assumed to be perfect if the wasted energy transfer is able to be excluded

What is an example of a ‘perfect energy transfer‘

a pendulum constantly switching between KE and GPE

What is wasted energy

Energy that cannot be ‘gathered’ for any specific use

ways energy is dissipated

Heat loss to the surroundings

Work done against air resistance

Work done against friction

How does friction act as a means of wasted energy transfers?

Heats up working parts, causing energy to transfer from the kinetic store to the thermal store of the surroundings

How can energy transfer waste by friction be reduced?

Lubrication of the parts that rub together

ways to reduce energy loss

lubrication

Insulation

how does lubrication reduce energy loss

Reduces the amount of friction between working parts

how does insulation reduce energy loss

Reduces energy transfer via conduction by reducing the passing of vibration of particles which is how energy is conducted

three factors of quality of insulation

thermal conductivity

density

thickness

How does thermal conductivity affect the insulation of a material?

The lower it is, the less energy is transferred

Lower the better

How does density affect the insulation of a material?

The more dense an insulator the more conduction can occur as the particles would be closer together allowing for energy transfer between them to be more easier

Lower the better

How does thickness affect the insulation of a material?

Increasing the thickness of an insulation material improves its thermal resistance

thicker the better

How are house lofts often insulated

Glass fibre as there is air trapped between woven fibres which reduces density

Glass can’t conduct heat that well as well, thus it is suitable for insulation

How are gaps between external walls insulated?

Cavity wall insulation

This is often done by drilling a hole through the external wall to reach the cavity and filling it with a special type of foam which is made from blown mineral fibre filled with gas

This lowers the conduction of heat through the walls from the inside to the outside

power

the rate of energy transfer or the rate of work done

power equation

P = E/t

P = power, measured in watts (W)

E = energy transferred or work done, measured in joules (J)

t = time, measured in seconds (s)

1 watt is equal to…

1 joule per second

1 J/s

efficiency

The ratio of the useful energy output from a system to its total energy output

efficiency equation

useful energy output / total energy input

(can be power instead of energy)

force

a push/pull that acts on an object due to the interaction with another object

3 impacts of forces on another objects

They can change their speed

They can change their direction

They can change their shape

weight force

a gravitational force experienced by any mass in a gravitational field

electrostatic force

the force experienced by any charged object in an electric field

thrust

the force causing an object to move such as the force from a rocket engine

air resistance/drag

an object moving through the air experiences air resistance due to collisions between the object and the air particles

upthrust

the force of a fluid (such as water) pushing an object upwards (making it float)

compression

forces that act inward on an object squeezing it

magnetic force

a force experienced between magnetic poles that can be attractive/repulsive

friction

a force that opposes motion

Occurs when objects rub against eachother

tension

an object that is being stretched experiences a tension force

reaction force/normal force

an object at rest on a surface experiences reaction force. this is at right angle to the surface hence the ‘normal’ reaction. anytime 2 objects are in contact there is a reaction force

contact force

a force which acts between objects that are physically touching

examples of contact forces

friction

air resistance

tension

reaction/normal force

non contact force

a force which acts at a distance without any contact between bodies due to the action of a field

examples of non contact forces

gravitational

electrostatic

magnetic

scalars

quantities with only a magnitude

examples of scalar quantities

distance, speed, mass, energy, volume, density, temperature, power

vectors

quantities with both magnitudes and directions

examples of vector quantities

displacement, velocity, weight, force, acceleration, momentum

Newton’s Third Law

if object A exerts a force on object B, object B will exert an equal and opposite force on object A. (Every action has an equal and opposite reaction)

How to draw scale diagrams

Step 1: Link the vectors head-to-tail if they aren’t already

Step 2: Draw the resultant vector using the triangle or parallelogram method

Step 3: Measure the length of the resultant vector using a ruler

Step 4: Measure the angle of the resultant vector (from North if it is a bearing) using a protractor

When is an object in equilibrium?

When there is no resultant force acting on it

What happens to an object as a result of it being in equilibrium?

Remains at rest or at constant velocity (Newton’s first law)

How to draw free body diagrams?

Each force is represented as a vector arrow, where each arrow:

Is scaled to the magnitude of the force it represents

Points in the direction that the force acts

Is labelled with the name of the force it represents

What is the resultant force of an object with balanced forces acting on it?

0N

moment

the turning effect of a force about a pivot