The eight main energy stores

Energy can be stored in different ways within objects or systems. These stores hold energy until it is transferred or changed into another form. There are eight key energy stores that help us understand how energy works in the world around us.

Types of energy stores

• Thermal - Energy stored in an object due to its temperature, related to the movement of its particles
• Kinetic - Energy stored in a moving object, depending on its speed and mass
• Gravitational potential - Energy stored in an object based on its height above the ground, which can be released when it falls
• Elastic potential - Energy stored in stretched or compressed objects, like a spring or rubber band, that can return to their original shape
• Chemical - Energy stored in the bonds between atoms in substances, such as in food, fuel, or batteries
• Magnetic - Energy stored in the fields created by magnets or magnetic materials when they attract or repel
• Electrostatic - Energy stored in charged objects, created by the attraction or repulsion between positive and negative charges
• Nuclear - Energy stored in the nucleus of atoms, released during processes like nuclear reactions

Each store represents a different way energy can be held, and energy can move from one store to another through various transfers.

Four ways energy can be transferred

Energy does not stay in one place forever. It moves between stores or objects through specific methods. There are four main ways this transfer happens, each suited to different situations.

Methods of energy transfer

• Mechanical through forces - Energy moves when a force acts on an object, such as pushing or pulling, which can change the object's motion or shape
• Electrical through circuits - Energy flows as electric current in wires and components, powering devices like lights or motors
• Heating from hot to cold objects - Energy transfers naturally from warmer objects to cooler ones until temperatures even out
• Radiation through waves - Energy travels as waves, like light or infrared, without needing a medium, such as heat from the sun reaching Earth

These transfers allow energy to shift between the eight stores, making systems work efficiently.

How interacting objects use forces to transfer energy

When two objects interact, they exert forces on each other. These forces are always equal in size but opposite in direction, following basic rules of physics. This interaction causes energy to transfer from one object's store to another's, changing how the energy is held.

Key features of force-based energy transfer

• Equal forces - If object A pushes on object B with a certain force, object B pushes back on object A with the exact same force strength
• Energy movement between stores - The forces cause energy to shift, for example, from kinetic in one object to thermal in another
• Examples of interaction - When a ball hits a wall, the force transfers kinetic energy from the ball to elastic potential in the wall, or to thermal if there's friction

This process shows how everyday actions, like throwing or catching, involve energy transfers through balanced forces.

Energy conservation during changes between stores

Energy is never created or destroyed—it only changes form. This is the principle of energy conservation. When energy shifts in a system, especially involving kinetic energy, the changes happen at the same time to keep the total energy the same.

How energy conservation works

• Simultaneous changes - If kinetic energy decreases in one part of a system, it must increase in another store or transfer method right away to balance out
• No energy loss - The total amount stays constant, though some energy might end up as less useful forms like thermal spread out in the surroundings

Example: Energy conservation in car braking

1. A moving car has kinetic energy in its motion.
2. When the driver applies the brakes, friction forces act between the brake pads and wheels.
3. These forces transfer the car's kinetic energy to thermal energy in the brake system.
4. The kinetic energy decreases while thermal energy increases at the same time, conserving the total energy.