GCSE — physicsFoundational6 min read

Energy Stores and Systems

Kinetic, gravitational potential, elastic, thermal, chemical, nuclear, magnetic energy stores

Tutor AI Team
Tutor AI Team

# Energy Stores and Systems — GCSE Physics

Energy is one of the most fundamental concepts in physics. It cannot be created or destroyed — only transferred from one store to another. Understanding energy stores and how energy moves between them is essential for GCSE Physics.

1. What Is Energy?

Energy is the capacity to do work or cause change. It is measured in joules (J).

  • 1 joule = the energy transferred when a force of 1 N moves through 1 m
  • 1 kilojoule (kJ) = 1000 J
  • 1 megajoule (MJ) = 1,000,000 J

The Law of Conservation of Energy

Energy cannot be created or destroyed — it can only be transferred from one store to another or transformed from one form to another.

The total energy of a closed system always stays the same.

2. Energy Stores

Energy is stored in different ways. GCSE Physics recognises eight energy stores:

Energy Store Description Example
Kinetic Energy of a moving object A rolling ball, a running person
Gravitational Potential (GPE) Energy of an object raised above the ground A book on a shelf, water behind a dam
Elastic Potential Energy stored in a stretched or compressed object A stretched spring, a drawn bow
Thermal Energy related to the temperature of an object A hot cup of tea, a warm radiator
Chemical Energy stored in chemical bonds Food, fuel, batteries
Nuclear Energy stored in the nucleus of an atom Uranium fuel, the Sun
Magnetic Energy stored in magnetic fields Two repelling magnets held close together
Electrostatic Energy of separated electric charges A charged balloon near a wall

3. Energy Transfers

Energy moves between stores by four main pathways:

Transfer Pathway Description Example
Mechanically By a force moving an object Pushing a box, stretching a spring
Electrically By electric current flowing A battery powering a lamp
By heating Due to temperature difference Hot drink warming your hands
By radiation Electromagnetic waves (light, IR, etc.) Sun warming the Earth, a light bulb

4. Examples of Energy Transfers

A Ball Being Thrown Upwards

  1. Chemical store (in muscles) → kinetic store (ball moving upwards)
  2. Kinetic store → gravitational potential store (ball gains height, slows down)
  3. At the top: all kinetic energy has been converted to GPE
  4. As it falls: GPE store → kinetic store

A Car Braking

  1. Kinetic store (moving car) → thermal store (brake pads and discs heat up)
  2. Some energy also transferred to the thermal store of the surroundings by heating

An Electric Kettle

  1. Chemical store (power station fuel) → electrical transfer → thermal store (water heats up)
  2. Some energy wasted to thermal store of surroundings

A Stretched Catapult Firing a Stone

  1. Elastic potential store → kinetic store (stone moves)
  2. Kinetic store → gravitational potential store (if stone goes upwards)

5. Energy Calculations

Kinetic Energy

KE=12mv2\boxed{KE = \frac{1}{2}mv^2}

Where:

  • KEKE = kinetic energy (J)
  • mm = mass (kg)
  • vv = velocity (m/s)

Gravitational Potential Energy

GPE=mgh\boxed{GPE = mgh}

Where:

  • GPEGPE = gravitational potential energy (J)
  • mm = mass (kg)
  • gg = gravitational field strength (N/kg)
  • hh = height (m)

Elastic Potential Energy

EPE=12ke2\boxed{EPE = \frac{1}{2}ke^2}

Where:

  • EPEEPE = elastic potential energy (J)
  • kk = spring constant (N/m)
  • ee = extension (m)

Worked Example: Kinetic Energy

Problem

Question: Calculate the kinetic energy of a 50 kg runner moving at 8 m/s.

KE=12mv2=12×50×82=12×50×64=1600 JKE = \frac{1}{2}mv^2 = \frac{1}{2} \times 50 \times 8^2 = \frac{1}{2} \times 50 \times 64 = 1600 \text{ J}

Solution

Worked Example: GPE

Problem

Question: A 2 kg book is placed on a shelf 1.5 m above the ground. Calculate the increase in GPE. (g=9.8g = 9.8 N/kg)

GPE=mgh=2×9.8×1.5=29.4 JGPE = mgh = 2 \times 9.8 \times 1.5 = 29.4 \text{ J}

Solution

Worked Example: Conservation of Energy

Problem

Question: A 0.5 kg ball is dropped from a height of 10 m. Calculate its speed just before hitting the ground. (g=9.8g = 9.8 N/kg)

Solution

GPE at top converts entirely to KE at bottom: mgh=12mv2mgh = \frac{1}{2}mv^2 0.5×9.8×10=12×0.5×v20.5 \times 9.8 \times 10 = \frac{1}{2} \times 0.5 \times v^2 49=0.25v249 = 0.25v^2 v2=196v^2 = 196 v=14 m/sv = 14 \text{ m/s}

Worked Example: Elastic PE

Problem

Question: A spring with spring constant 200 N/m is stretched by 0.15 m. Calculate the elastic potential energy stored.

EPE=12ke2=12×200×0.152=12×200×0.0225=2.25 JEPE = \frac{1}{2}ke^2 = \frac{1}{2} \times 200 \times 0.15^2 = \frac{1}{2} \times 200 \times 0.0225 = 2.25 \text{ J}

Solution

7. Systems and Energy

A system is an object or group of objects. When we analyse energy transfers, we define the system and track energy flowing in and out.

Closed system: No energy enters or leaves — total energy stays constant.

Open system: Energy can enter or leave (e.g., heat escaping to surroundings).

In reality, most systems are open — energy "leaks" to the thermal store of the surroundings.

8. Practice Questions

    1. List the eight energy stores. (4 marks)
    1. Describe the energy transfers when a car accelerates from rest. (3 marks)
    1. Calculate the kinetic energy of a 1500 kg car travelling at 20 m/s. (2 marks)
    1. A 60 kg person climbs stairs to a height of 4 m. Calculate the increase in GPE. (g=9.8g = 9.8 N/kg) (2 marks)
    1. A ball of mass 0.2 kg is thrown vertically upwards at 10 m/s. Calculate the maximum height reached. (g=9.8g = 9.8 N/kg) (3 marks)

    Answers

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Frequently Asked Questions

Are "forms of energy" the same as "energy stores"?

The GCSE specification uses "energy stores" rather than "forms of energy" (like kinetic energy, potential energy). The concept is the same but the language is updated.

What is "wasted" energy?

Energy transferred to unwanted stores, usually the thermal store of the surroundings. It isn't "lost" — it's just not useful anymore.

Why can't we reuse wasted thermal energy?

Energy spreads out (dissipates) and the temperature difference becomes too small to be useful. This is related to the Second Law of Thermodynamics.

Summary

  • Energy is measured in joules (J) and is always conserved
  • Eight energy stores: kinetic, GPE, elastic PE, thermal, chemical, nuclear, magnetic, electrostatic
  • Four transfer pathways: mechanically, electrically, by heating, by radiation
  • Key equations: KE=12mv2KE = \frac{1}{2}mv^2, GPE=mghGPE = mgh, EPE=12ke2EPE = \frac{1}{2}ke^2
  • Energy transfers can be tracked through systems
  • "Wasted" energy is transferred to unwanted thermal stores
Tags:
#gcse#physics#energy#energy-stores#energy-transfer

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