What Is Energy?
Energy is one of the most fundamental concepts in all of science — and one of the most misunderstood. You cannot see energy directly, but you can observe what it does: it makes things move, heat up, light up, or change.
The capacity to do work or cause a change. Energy is measured in joules (J).
A key rule that governs everything in physics:
The Law of Conservation of Energy: Energy cannot be created or destroyed — it can only be transferred from one store to another, or converted from one form to another. The total energy in a closed system always remains the same.
Think of energy like money in a bank account. You can move it around, spend it on different things, or save it — but you can never make money appear from nothing, and it never simply vanishes.
Imagine you have a gift card with €50 on it. You can spend it on food, clothes, or entertainment — but you can never spend more than €50 total. Energy works the same way: you can use it in different ways, but the total always stays the same.
MYP Connection: In MYP Sciences, this topic sits within the key concept of Systems and Change and the related concept of Energy and Transformation. Understanding how energy moves through systems — from one store to another — is at the heart of this unit.
Energy Stores
Scientists use the idea of energy stores to describe where energy is 'held' or 'kept' at any given moment. Think of a store as a container holding energy, ready to be used.
Here are the five core energy stores you need to know for MYP 4:
Energy held by an object in motion. The faster it moves and the greater its mass, the more kinetic energy it stores.
Energy held by an object due to its height above a reference point (usually the ground). The higher up and the heavier it is, the more energy is stored.
Energy stored in a stretched or compressed object, such as a spring, rubber band, or elastic material.
Energy stored in the bonds between atoms in substances such as food, fuel, and batteries. This energy is released during chemical reactions.
Energy stored due to the temperature of an object. The hotter it is and the greater its mass, the more thermal energy it holds.
A helpful memory phrase for the five core stores: 'King George Eats Cold Toast' — Kinetic, Gravitational PE, Elastic PE, Chemical, Thermal. These five stores cover the vast majority of MYP questions.
Extension stores (beyond MYP 4 core):
Energy stored in the nucleus of an atom. Released during nuclear reactions (fission or fusion). Note: nuclear fuels do not trace their energy to the Sun — this energy originates from stellar processes.
Energy stored due to the relative positions of charged objects in an electric field. For example, two opposite charges held apart store energy because work must be done against the attractive force to keep them separated — analogous to how a stretched spring stores elastic PE.
Nuclear and electrostatic stores are included here for completeness but are not typically assessed at MYP 4. Focus your revision on the five core stores above.
10 more sections in this topic
Pick this up in your Library: it holds the whole topic, notes, cheatsheet and questions.