energy stores , transfers , density , particle model and power

What are the main energy stores in AQA GCSE Physics?

The main energy stores are: thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear energy stores. Diagram needed? No.

What does the kinetic energy store mean?

The kinetic energy store is the energy store of a moving object. The faster an object moves and the greater its mass, the more energy it has in its kinetic energy store. Diagram needed? Optional — moving car.

What does the thermal energy store mean?

The thermal energy store is linked to the temperature of an object. The hotter the object, the more energy it has in its thermal energy store. Diagram needed? Optional — hot object particles moving.

What does the gravitational potential energy store mean?

The gravitational potential energy store is the energy store of an object due to its position in a gravitational field. The higher an object is lifted, the more energy it gains in its gravitational potential energy store. Diagram needed? Yes — object lifted above ground.

What does the elastic potential energy store mean?

The elastic potential energy store is the energy stored in an object when it is stretched or compressed, such as a spring, elastic band or trampoline. Diagram needed? Yes — stretched spring.

What does the chemical energy store mean?

The chemical energy store is energy stored in chemical bonds. Examples include food, fuels and batteries. Diagram needed? No.

What does the nuclear energy store mean?

The nuclear energy store is energy stored inside atomic nuclei. It can be released in nuclear reactions such as fission or fusion. Diagram needed? No.

What is a system in physics?

A system is a single object or a group of objects being studied. For example, a ball, a kettle, a phone, a car, or two colliding vehicles can all be systems. Diagram needed? Optional.

What happens when a system changes?

When a system changes, energy is transferred. Energy can be transferred into the system, away from the system, between objects in the system, or between different energy stores. Diagram needed? Yes — arrows between energy stores.

What is a closed system?

A closed system is a system where matter and energy cannot enter or leave. The total energy in a closed system stays the same. Diagram needed? Optional — sealed flask.

What is the net change in energy in a closed system?

The net change in energy in a closed system is zero because energy cannot enter or leave the system. Diagram needed? No.

What does conservation of energy mean?

Conservation of energy means energy can be transferred usefully, stored or dissipated, but it can never be created or destroyed. Diagram needed? No.

What does dissipated energy mean?

Dissipated energy is energy that has been transferred to less useful stores, usually thermal energy stores of the surroundings. It is often called “wasted” energy. Diagram needed? Optional.

Why is energy never actually “used up”?

Energy is not used up because it cannot be destroyed. Instead, it is transferred between energy stores. Some of it may be dissipated to the surroundings, making it less useful. Diagram needed? No.

What are the main ways energy can be transferred?

Energy can be transferred mechanically, electrically, by heating, or by radiation such as light or sound. Diagram needed? Yes — four transfer pathways.

What does energy transferred mechanically mean?

Energy is transferred mechanically when a force acts on an object and causes it to move. This is also called work done. Diagram needed? Yes — force moving object.

What does energy transferred electrically mean?

Energy is transferred electrically when moving charges do work in a circuit. For example, energy is transferred from a battery to components in a circuit. Diagram needed? Optional — circuit.

What does energy transferred by heating mean?

Energy is transferred by heating when energy moves from a hotter object or region to a cooler one, increasing the thermal energy store of the cooler object. Diagram needed? Optional — kettle heating water.

What does energy transferred by radiation mean?

Energy can be transferred by radiation, such as light or infrared radiation. For example, the Sun transfers energy to Earth by radiation. Diagram needed? Optional.

What is work done?

Work done means energy transferred by a force. If a force causes an object to move, energy is transferred and work is done. Diagram needed? Yes.

Energy transfer when a ball is thrown upwards.

When a person throws a ball upwards, energy is transferred chemically from the person’s arm muscles to the kinetic and gravitational potential energy stores of the ball. Diagram needed? Yes — ball thrown upwards.

Energy transfer when a ball falls.

When a ball falls, energy is transferred from its gravitational potential energy store to its kinetic energy store. Diagram needed? Yes — falling ball.

Energy transfer when a car brakes.

When a car brakes, friction between the brakes and wheels transfers energy from the car’s kinetic energy store to the thermal energy stores of the brakes, wheels and surroundings. Diagram needed? Yes — car braking.

Energy transfer in a collision.

In a collision, the normal contact force does work. Energy is transferred from the car’s kinetic energy store to other stores, such as elastic potential energy stores and thermal energy stores of the objects involved. Diagram needed? Yes — collision.

What does kinetic energy depend on?

Kinetic energy depends on the mass of the object and its speed. Greater mass and greater speed mean more kinetic energy. Diagram needed? Optional.

Formula for kinetic energy.

Kinetic energy = ½ × mass × speed². Ek = ½mv² Ek is in joules, mass is in kilograms, and speed is in metres per second. Diagram needed? Yes — formula triangle or labelled equation.

Why does speed have a large effect on kinetic energy?

Speed is squared in the kinetic energy equation, so doubling the speed makes the kinetic energy four times larger. Diagram needed? No.

What does gravitational potential energy depend on?

Gravitational potential energy depends on mass, gravitational field strength and height. Greater mass, height or gravitational field strength means more gravitational potential energy. Diagram needed? Yes — object raised.

Formula for gravitational potential energy.

Gravitational potential energy = mass × gravitational field strength × height. Ep = mgh Ep is in joules, mass is in kg, g is in N/kg, and height is in metres. Diagram needed? Yes — labelled equation.

What happens to energy when an object falls with no air resistance?

If there is no air resistance, the energy lost from the gravitational potential energy store equals the energy gained in the kinetic energy store. Diagram needed? Yes — GPE → KE.

What happens to energy when an object falls with air resistance?

With air resistance, some energy is transferred to the thermal energy stores of the object and surroundings, so not all gravitational potential energy becomes kinetic energy. Diagram needed? Yes — falling object with air resistance.

What is elastic potential energy?

Elastic potential energy is energy stored in an object when it is stretched or compressed. Diagram needed? Yes — stretched spring.

Formula for elastic potential energy.

Elastic potential energy = ½ × spring constant × extension². Ee = ½ke² Ee is in joules, k is in N/m, and e is in metres. Diagram needed? Yes — spring with extension.

When can you use the elastic potential energy equation?

You can use Ee = ½ke² only if the limit of proportionality has not been exceeded. Diagram needed? Optional — force-extension graph.

What is power?

Power is the rate of energy transfer or the rate of doing work. It tells you how much energy is transferred each second. Diagram needed? No.

What is the unit of power?

Power is measured in watts, W. One watt means one joule of energy transferred per second. Diagram needed? No.

Formula linking power, energy and time.

Power = energy transferred ÷ time. P = E ÷ t Power is in watts, energy is in joules, and time is in seconds. Diagram needed? Yes — formula triangle.

Formula linking power, work done and time.

Power = work done ÷ time. P = W ÷ t Power is in watts, work done is in joules, and time is in seconds. Diagram needed? Yes.

What does a more powerful machine do?

A more powerful machine transfers energy faster. It may do the same amount of work in less time, or transfer more energy in the same time. Diagram needed? No.

Why is a powerful car not necessarily more efficient?

A powerful car transfers energy quickly, but it may also waste a lot of energy. Power is about the rate of energy transfer, while efficiency is about the proportion of energy transferred usefully. Diagram needed? No.

Why does friction waste energy?

When objects move against each other, friction transfers energy from useful kinetic stores to thermal energy stores. This dissipates energy to the surroundings. Diagram needed? Yes — rubbing surfaces heating.

How does lubrication reduce wasted energy?

Lubricants reduce friction between surfaces. This means less energy is dissipated to thermal energy stores, so more energy is transferred usefully. Diagram needed? Optional — oil between surfaces.

What are lubricants usually like?

Lubricants are usually liquids, such as oil, because they can flow between surfaces and coat them. Diagram needed? No.

What is efficiency?

Efficiency is the proportion of the total input energy or power that is transferred usefully. Diagram needed? No.

Formula for efficiency using energy.

Efficiency = useful output energy transfer ÷ total input energy transfer. To convert to a percentage, multiply by 100. Diagram needed? Yes — formula triangle.

Formula for efficiency using power.

Efficiency = useful power output ÷ total power input. To convert to a percentage, multiply by 100. Diagram needed? Yes.

How can efficiency be improved?

Efficiency can be improved by reducing wasted energy transfers. This can be done by lubrication, insulation or streamlining. Diagram needed? Optional.

Why is no device 100% efficient?

Most devices waste some energy, usually by transferring energy to thermal energy stores of the surroundings. This means the useful output is less than the total input. Diagram needed? No.

Why are electric heaters often considered 100% efficient?

Electric heaters are usually considered 100% efficient because all the electrical energy is transferred to the useful thermal energy store. Diagram needed? No.

What is specific heat capacity?

Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1°C. Diagram needed? No.

Why do different substances heat up at different rates?

Different substances have different specific heat capacities. A substance with a high specific heat capacity needs more energy to increase its temperature. Diagram needed? Optional.

Formula for specific heat capacity.

Change in thermal energy = mass × specific heat capacity × change in temperature. ΔE = mcΔθ Energy is in joules, mass is in kg, specific heat capacity is in J/kg°C, and temperature change is in °C. Diagram needed? Yes — labelled equation.

What does a high specific heat capacity mean?

A high specific heat capacity means a substance needs a lot of energy to increase its temperature by a small amount. Diagram needed? No.

How do you investigate specific heat capacity of a solid?

Measure the mass of the block, wrap it in insulation, insert a heater and thermometer, connect the heater to a power supply, measure the starting temperature, switch on the heater, record temperature and current at regular intervals, then calculate energy transferred and use ΔE = mcΔθ. Diagram needed? Yes — block, heater, thermometer circuit.

Why is insulation used in the specific heat capacity practical?

Insulation reduces energy transfer to the surroundings, so more of the electrical energy supplied heats the block. This makes the result more accurate. Diagram needed? Optional.

How is energy transferred to the block in the specific heat capacity practical?

The current does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. Energy is then transferred by heating to the block’s thermal energy store. Diagram needed? Yes.

How do you calculate energy transferred by a heater?

Use E = Pt, where energy transferred equals power multiplied by time. If power is not given, calculate power using P = VI. Diagram needed? Yes — formula links.

How can a graph be used to find specific heat capacity?

Plot temperature against energy transferred. The gradient is temperature change divided by energy transferred. Since ΔE = mcΔθ, specific heat capacity can be calculated using c = 1 ÷ (gradient × mass). Diagram needed? Yes — temperature-energy graph.

What is density?

Density is the mass per unit volume of a substance. It tells you how tightly packed the particles are. Diagram needed? Yes — particles close vs spread out.

Formula for density.

Density = mass ÷ volume. ρ = m ÷ V Density is usually measured in kg/m³ or g/cm³. Diagram needed? Yes — formula triangle.

What does high density mean?

High density means a substance has a lot of mass in a small volume, usually because its particles are tightly packed. Diagram needed? Yes.

How are particles arranged in a solid?

In a solid, particles are held close together in a fixed, regular arrangement by strong forces. They vibrate around fixed positions. Diagram needed? Yes — solid particle diagram.

How are particles arranged in a liquid?

In a liquid, particles are close together but arranged irregularly. They can move past each other in random directions. Diagram needed? Yes — liquid particle diagram.

How are particles arranged in a gas?

In a gas, particles are far apart with almost no forces of attraction. They move randomly at high speeds. Diagram needed? Yes — gas particle diagram.

Which state is usually most dense?

Solids are usually the most dense because their particles are packed closely together. Diagram needed? Optional.

How do you find the density of a regular solid?

Measure its mass using a balance. Measure its dimensions with a ruler and calculate its volume using the correct formula. Then use density = mass ÷ volume. Diagram needed? Yes — cuboid with dimensions.

How do you find the density of an irregular solid?

Measure its mass using a balance. Place it into a eureka can filled with water. Measure the volume of water displaced, which equals the volume of the object. Then calculate density using mass ÷ volume. Diagram needed? Yes — eureka can.

How do you find the density of a liquid?

Place a measuring cylinder on a balance and zero it. Pour in a known volume of liquid and record its mass. Repeat for different volumes and calculate density using mass ÷ volume, then find a mean. Diagram needed? Yes — measuring cylinder on balance.

Why repeat measurements when finding density of a liquid?

Repeating measurements allows you to calculate a mean, reducing the effect of random errors. Diagram needed? No.

What is internal energy?

Internal energy is the total energy stored by the particles in a system in their kinetic and potential energy stores. Diagram needed? Yes — particles moving and spacing.

What is kinetic energy in particles?

It is energy due to the movement or vibration of particles. Hotter particles have more kinetic energy on average. Diagram needed? Optional.

What is potential energy in particles?

It is energy due to the positions of particles and the forces between them. It changes when bonds between particles are broken or formed. Diagram needed? Optional.

What happens when a system is heated?

Heating transfers energy to the particles, increasing internal energy. This can cause a rise in temperature or a change of state. Diagram needed? Yes.

What happens to particles when temperature increases?

The particles gain energy in their kinetic energy stores and move or vibrate faster. Diagram needed? Yes — before/after particle motion.

What happens during a change of state?

During a change of state, energy changes the potential energy stores of the particles by breaking or forming bonds, rather than changing temperature. Diagram needed? Yes — heating curve.

Why does temperature stay constant during melting or boiling?

The energy transferred is used to overcome forces between particles and increase their potential energy stores, not to increase their kinetic energy stores. Diagram needed? Yes — heating curve.

Is a change of state physical or chemical?

A change of state is a physical change because no new substance is formed. The substance is the same, but in a different state. Diagram needed? No.

Why is mass conserved during a change of state?

The number of particles stays the same. The particles are only arranged differently, so no mass is lost. Diagram needed? Optional.

What is melting?

Melting is when a solid changes into a liquid. Diagram needed? Yes — solid to liquid.

What is freezing?

Freezing is when a liquid changes into a solid. Diagram needed? Yes.

What is boiling or evaporating?

Boiling or evaporating is when a liquid changes into a gas. Diagram needed? Yes.

What is condensing?

Condensing is when a gas changes into a liquid. Diagram needed? Yes.

What is sublimation?

Sublimation is when a solid changes directly into a gas. Diagram needed? Yes.

How do gas particles move?

Gas particles move constantly in random directions at a range of speeds. Diagram needed? Yes — random motion arrows.

How do gas particles create pressure?

Gas particles collide with the walls of a container. Each collision exerts a force on the wall. The total force exerted over an area creates pressure. Diagram needed? Yes — particles hitting container wall.

What is gas pressure?

Gas pressure is the force exerted by gas particles per unit area of the container wall. Diagram needed? Optional.

How is temperature related to particle kinetic energy?

The temperature of a gas is related to the average energy in the kinetic energy stores of its particles. Higher temperature means higher average kinetic energy. Diagram needed? Yes.

What happens to gas particles when temperature increases?

When temperature increases, gas particles gain kinetic energy and move faster on average. Diagram needed? Yes.

Why does heating a gas increase pressure if volume is constant?

Particles move faster, collide with the container walls more often, and exert a greater force during each collision. This increases pressure. Diagram needed? Yes.

How can doing work on a gas increase its temperature?

Doing work on a gas transfers energy to its particles’ kinetic energy stores, increasing their average speed and therefore increasing the temperature. Diagram needed? Yes — bike pump.

Why does a bike pump get warm?

When you push the plunger, you do work on the gas. Energy is transferred to the kinetic energy stores of the gas particles, increasing the gas temperature and making the pump warmer. Diagram needed? Yes.

What happens to gas pressure when temperature increases at constant volume?

Pressure increases because particles move faster, collide more frequently with the walls, and exert a greater force during collisions. Diagram needed? Yes.

What happens to gas pressure when temperature decreases at constant volume?

Pressure decreases because particles move more slowly, collide less frequently, and exert a smaller force during collisions. Diagram needed? Optional.

What happens to gas pressure when volume decreases at constant temperature?

Pressure increases because the particles are closer together and collide with the walls more frequently. Diagram needed? Yes — smaller container.

What happens to gas pressure when volume increases at constant temperature?

Pressure decreases because the particles are more spread out and collide with the walls less frequently. Diagram needed? Yes — larger container.

What is the relationship between pressure and volume for a fixed mass of gas at constant temperature?

Pressure and volume are inversely proportional. When volume increases, pressure decreases. When volume decreases, pressure increases. Diagram needed? Yes — pressure-volume graph.

Equation for pressure and volume.

For a fixed mass of gas at constant temperature: pV = constant This means pressure × volume stays the same. Diagram needed? Yes — equation.

Why can a gas container expand or compress?

Gas pressure creates a net outward force on the container walls. If the container can change size, differences between inside and outside pressure can cause it to expand or compress. Diagram needed? Yes — balloon.

Why does a helium balloon expand as it rises?

Atmospheric pressure decreases with height. The pressure outside the balloon becomes lower, so the gas inside expands until the inward and outward forces balance. Diagram needed? Yes — balloon rising.

How do electrical appliances transfer energy?

Electrical appliances transfer energy electrically from cells, batteries or mains supplies to components in a circuit when current flows. Diagram needed? Optional.