GCSE Physics - Topic 1

What happens when energy is transferred to an object?

It is stored in one of the object's energy stores

How do you remember the 8 energy stores?

KG (of) CEMENT

Kinetic energy stores

When something moves

Gravitational potential energy stores

When something is high up

Chemical energy stores

In batteries

Elastic potential energy stores

When something elastic is stretched

Magnetic energy stores

Magnets attracting or repelling

Electrostatic energy stores

Static on a balloon

Nuclear energy stores

Inside atoms

Thermal energy stores

When something heats up

What is another word for thermal energy stores?

Internal energy stores (but this is not the same as internal energy)

What do methods of energy transfer describe?

How energy is moving between objects in a system

What are the 4 methods of energy transfer?

Heating (of particles) - increasing internal energy
Electrically (work done by moving charges)
Radiation e.g light / sound / infared (heat)
Mechanically (work done by a force)

What is a system?

An object or group of objects

What happens when a system changes?

There are changes in the way energy is stored

How can energy be transferred within a system?

Transferred into the system
Transferred away from the system
Transferred between different objects in a system
Transferred between different types of energy stores

What is a closed system?

Neither matter nor energy can leave - the net change in the total energy of a closed system is always zero

In physics what do you always do?

Used close systems (otherwise describing energy transfers would be never ending as energy is never destroyed)

How is energy described when transferred in a single object system? (a bungee jumper jumping off a bridge)

When the bungee jumper is at the bottom of their jump

How is energy described when transferred in a single object system? (the wind causes a windmill to spin)

When the wind turns the windmill

How is energy described when transferred in a two object system? (the heating of a kettle

which then heats up water)

What does "work done" mean?

It is the same as saying "energy transferred"

When can work be done?

When current flows (work is done against resistance in a circuit)
By a force moving an object

Why won't these following examples have a method of energy transfer?

Because the work done is the method of energy transfer

How does throwing a ball upwards do work?

The initial force exerted by a person throwing a ball upwards does work
It causes energy to be transferred from the chemical energy store of the person's arm to the kinetic energy store of the their arm
Then energy is transferred mechanically from the kinetic energy store of their arm to the kinetic energy store of the ball

How does an object accelerated by a constant force do work? (e.g a ball dropped from a height)

The ball is accelerated by gravity - the gravitational force does work
It causes energy to be transferred from the ball's gravitational potential energy store to the kinetic energy store of the ball

How does a vehicle slowing down do work?

The friction between a car's brakes and its wheels does work as it slows down
It causes energy to be transferred from the kinetic energy store of the wheels to the thermal energy store of the surroundings

How does a moving object hitting an obstacle do work?

In the collision between a stationary object and a constant force (e.g a moving car)

If asked to describe an energy transfer

what is useful to know? (But this will be covered in a later topic)

What energy store is involved when an object is moving?

Kinetic energy store

When is energy transferred into an objects kinetic energy store? (Very important)

ONLY when an object speeds up

When is energy transferred away from an objects kinetic energy store? (and into a different store)

When an object slows down

What does the energy in an object's kinetic energy store depend on?

The object's mass and speed

Therefore an object with a greater mass

that is moving faster will...

What is the formula for calculating kinetic energy?

Ek (k in subscript) = 1/2mv2

Kinetic energy (J) = 1/2 x mass (kg) x velocity squared (m/s)

What must you remember about this equation?

Don't put the fraction "1/2" into your calculator

What does lifting an object in a gravitational field require?

Work done - this causes a transfer of energy to the gravitational potential energy store of the raised object

What happens the higher an object is lifted?

The more energy is transferred to this store

What does the amount of energy in the GPE store depend on?

An object's mass

What is the equation for calculating the amount of energy in an object's GPE store?

Egrav (grav in subscript) = m x g x ∆h

GPE (J) = mass (kg) x gravitational field strength (N/kg) x change in height (m)

Unless the questions specifies otherwise

what is the gravitational field strength on earth?

What happens when an object falls?

Energy from its GPE store is transferred to its kinetic energy store

So what is a helpful equation for falling objects (when there is no air resistance)?

Energy lost from GPE store = energy gained in kinetic energy store

Would that be the case in real life?

No

What would the air resistance do?

Causes some energy to be transferred to other energy stores e.g some energy would be dissipated as heat due to the air resistance

What does stretching / squashing an object do?

Transfer energy to its elastic potential energy store

What is the equation for calculating the elastic potential energy of a stretched spring?

E (el in subscript) = o.5 x k x e2

Elastic potential energy (J) = 0.5 x spring constant (N/m) x extension2 (m)

When is that equation only valid?

If the limit of proportionality has not been exceeded

What do you need to remember about this calculation?

It uses extension - not overall length. In some questions

What is a spring constant?

It tells us the amount of force required to stretch a spring by 1m (measured in N/m)

What is the equation for the spring constant? (Also known as Hooke's law)

Force (N) = Spring constant (k) x Extension (m)
F = ke (e is sometimes x)
- They are directly proportional

How do the two equations link?

E = o.5 x F x e
E = o.5 x ke x e
E = o.5 x ke2

What must you ALWAYS remember with equations?

Check for unit conversions first
Write out equations
Substitute numbers
Rearrange (so you don't loose as many marks if you rearrange wrong because you substituted the numbers correctly)
Solve

How can you calculate the amount of energy stored in / released from a system as its temperature changes?

ΔE = m x c x Δθ

Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg°C) x change in temperature (°C)

What is specific heat capacity?

The amount of energy needed to RAISE (not change) the temperature of 1kg of a substance by 1 degree C

Does specific hate capacity vary with material?

Yes - different materials have different specific heat capacities as SHC is just a way of saying how hard it is to heat something up

How does specific heat capacity vary with material?

More energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others e.g you need 4200J to warm up 1kg of water by 1C

If a material needs to gain lots of energy in their energy stores to warm up

what will they need to cool down?

Where can you find flashcards with more information on specific heat capacity?

Topic 3

What is power?

The rate at which energy is transferred / the rate at which work is done

What is power (EODM)?

A powerful machine is not necessarily one which can exert a strong force (although it usually ends up being that way). A powerful machine is one which transfers a lot of energy in a short space for time
E.g take two cars that are identical in every way apart from the power of their engines. Both cars race the same distance. The car with the more powerful energy will reach the finish line faster than the other car (it will transfer the same amount of energy (as they are going the same distance)

What are the two equations for power? 1/2

P = E/t

Power (W) = Energy transferred (J) x time (s)

What are the two equations for power? 2/2

P = W/t

Power (W) = Work done (J) x time (s)

What is the equivalent of 1 Watt?

An energy transfer of 1 Joule per second

What can't happen to energy? (Very important)

It CANNOT be created or destroyed

What is the conservation of energy principle?

ENERGY IS ALWAYS CONSERVED: energy can be transferred usefully

What is dissipation?

Spread out to the point where it can no longer be useful

What does this mean in terms of energy?

Energy is conserved - In a closed system

When energy is being transferred between stores

is all of the energy transferred usefully (into the store you want it to go)?

What is dissipated energy sometimes called?

Wasted energy because the energy is being stored in a way that is not useful

What is an example of this? (Mobile phone)

A mobile phone is a system. When you use it

What is thermal conductivity?

The rate at which energy can be transferred through a material (through conduction)

What is the unit for thermal conductivity?

There isn't one - it's just a number

What happens in materials with a high thermal conductivity?

They transfer energy between their particles quickly

Examples of a low conductivity material

Concrete

Example of a high conductivity material

Copper

What happens to materials with a high thermal conductivity?

The higher the thermal conductivity of a material

What is conduction?

The process where vibrating particles transfer energy to neighbouring particles

Describe the process of conduction 1/3

Energy transferred to an object by heating is transferred to the thermal store of the object. This energy is shared across the kinetic energy stores of the particles in the object

Describe the process of conduction 2/3

The particles in the part of the object being heated vibrate more and collide with each other more frequently. These collision cause energy to be transferred between the particles kinetic energy stores. This is conduction.

Describe the process of conduction 3/3

This process continues throughout the object until the energy is transferred to the other side of the object. It's then usually transferred to the thermal energy store of the surroundings (or anything else touching the object)

What is convection?

Where energetic particles move away from hotter to cooler regions

What two states can convection only occur in?

Liquids and gases

Describe the process of convection 1/3

Energy is transferred by heating to the thermal store of the liquid or gas. This energy is shared across the kinetic energy stores of the gas or liquid's particles (like in conduction)

Describe the process of convection 2/3

Unlike in solids

Describe the process of convection 3/3

Because liquids and gases can flow

Therefore why do liquids and gases usually transfer energy by convection instead of conduction?

Their particles are much more free to move around and more spread out

Where does heat always move to and from?

Moves from hot to cold

How does a radiator create convection currents in the air of a room? 1/3

Energy is transferred from the radiator to nearby air particles by conduction (the air particles collide with the radiator surface)
The air by the radiator becomes warmer and less dense

How does a radiator create convection currents in the air of a room? 2/3

This warm air rises and is replaced by cooler air

How does a radiator create convection currents in the air of a room? 3/3

This cycle repeats

What are the two ways you can reduce the amount of energy being transferred to uselessly?

Lubrication
Thermal insulation

What happens when an object moves?

There's usually at least one frictional force against it

What does this frictional force cause?

Energy in the system to be dissipated e.g air resistance can transfer energy from a falling object's kinetic energy store to its thermal energy store

What does lubrication do?

Reduce frictional forces

How does lubrication reduce frictional forces?

For objects being rubbed together

What are some examples of lubricants?

Lubricants are usually liquids (like oil)

What does insulation do?

Reduces the rate of energy transfer by heating

How can you prevent energy losses through heating in a house? 1/2

Have thick walls that are made from a material with a low thermal conductivity
- The thicker the walls and the lower the thermal conductivity

How can you prevent energy losses through heating in a house? 2/2

Use thermal insulation