Energy is transferred between several stores inside a closed system. What has happened to the total energy of that system?

There is no net change, so the total energy afterwards is equal to the total energy before.

A rubber ball is dropped and each bounce reaches a lower height than the last. Has energy been destroyed?

No, energy has been transferred to the thermal stores of the ball, the floor and the air, so the total energy is unchanged.

A toy car is given a push along a bench and eventually stops. Account for its energy as a closed system.

The energy in its kinetic store has been transferred to the thermal stores of the car, the bench and the air, so the total is unchanged.

OCR GCSE Combined Science Physics J250

Electricity

Topic overview Charge, and producing static electricity Transfer of electrons in charging and discharging Current as a rate of flow of charge Charge, current and time Series and parallel circuits, and circuit symbols Current, potential difference and resistance Resistors whose resistance changes, and investigating them Linear and non-linear circuit elements from graphs Net resistance in series and parallel Circuits for measurement, and electrical power

Energy

Topic overview Conservation of energy, and energy stores Energy changes on heating, and calculating them Energy of a moving body, a spring and a raised object Dissipation, and energy transfer in domestic devices Power ratings, and calculating efficiency Reducing unwanted energy transfer, and the rate of cooling

Forces

Topic overview Measuring distance and time, and calculating speed Converting units, and rates Vectors and scalars in motion Distance-time and velocity-time graphs Average speed, and the equations of uniform motion How objects interact, and forces as vectors Newton's first law Newton's second law Work done, and stored energy Power, and Newton's third law Stretching, bending and compressing; elastic and plastic Force and extension, linear and non-linear The spring constant, and work done in stretching Gravitational fields, weight and free fall Calculations with weight and gravitational field strength

Global Challenges

Topic overview Typical speeds and everyday accelerations Reaction time, stopping distance and the dangers of large decelerations Stopping distance, acceleration and collision force calculations Energy resources, and trends in their use The national grid, and step-up and step-down transformers Why the national grid is efficient, and power in a transformer Mains electricity: a.c., d.c. and the domestic supply Live, neutral and earth wires, and electrical danger

Magnetism and Magnetic Fields

Topic overview Permanent and induced magnets, and magnetic poles Magnetic fields, and the dipping compass The magnetic effect of a current, and solenoids

Matter

Topic overview How the atomic model changed, and the structure of the atom The size of atoms, and defining density Density of the states of matter, and density calculations Conservation of mass in changes of state Heating a system, and specific heat capacity Calculations with specific heat capacity and latent heat Gas molecules, temperature and pressure

Radioactivity

Topic overview Protons, neutrons and isotopes Unstable nuclei and the emissions they give out Balancing nuclear equations Electron energy levels, and radiation from atoms Half-life and the randomness of decay Penetration of alpha, beta and gamma Contamination and irradiation, and reducing the hazard

Waves in Matter

Topic overview Amplitude, wavelength, frequency and period The wave equation Transverse and longitudinal waves Modelling waves with ripples and sound Electromagnetic waves as transverse, and energy transfer Frequency and wavelength across the spectrum What our eyes detect, and light as an electromagnetic wave Uses of electromagnetic waves Hazards of ultraviolet, X-rays and gamma rays Investigating reflection and refraction of light

Energy

Conservation of energy, and energy stores

3 things to know
Paper 6 (Physics)

Overview

The law of conservation of energy, what a closed system is, why dissipated energy is not lost, and the store changes for thrown stones, braking cars, kettles and freewheeling cyclists.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What does the law of conservation of energy state?

Key term

What is meant by a closed system when energy transfers are being considered?

Key term

Why is it more accurate to say that energy has been dissipated than to say it has been lost?

Questions from this subtopic

Each one with the model answer underneath.

1
What does the law of conservation of energy state?
Model answer
Energy cannot be created or destroyed; it can only be transferred from one store to another or dissipated to the surroundings.
2
What is meant by a closed system when energy transfers are being considered?
Model answer
A system that exchanges no energy with anything outside it, so its total energy stays the same.
3
Energy is transferred between several stores inside a closed system. What has happened to the total energy of that system?
Model answer
There is no net change, so the total energy afterwards is equal to the total energy before.
4
A rubber ball is dropped and each bounce reaches a lower height than the last. Has energy been destroyed?
Model answer
No, energy has been transferred to the thermal stores of the ball, the floor and the air, so the total energy is unchanged.
5
Why is it more accurate to say that energy has been dissipated than to say it has been lost?
Model answer
The energy still exists, but it has spread out into the surroundings where it is no longer useful.
6
A toy car is given a push along a bench and eventually stops. Account for its energy as a closed system.
Model answer
The energy in its kinetic store has been transferred to the thermal stores of the car, the bench and the air, so the total is unchanged.

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Electricity

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