The Many Forms of Energy

What is energy?

Energy is the ability to do work — to make something move, change, heat up, or light up. Everything that happens, from a rolling ball to a beating heart, needs energy. In science we measure energy in joules (J).

Energy is not one single thing. It appears in many forms, and the most exciting part of physics is watching it change from one form into another.

The main forms of energy

Kinetic energy is the energy of motion. A sprinting runner, falling rain, and a flying ball all have kinetic energy. The faster and heavier something is, the more kinetic energy it carries.

Potential energy is stored energy waiting to be used. There are different types:

• Gravitational potential energy — stored by height. A rock at the top of a cliff has lots of it.
• Elastic potential energy — stored by stretching or squashing. A drawn bow or a compressed spring.

Chemical energy is stored in the bonds between atoms. Food, fuel, and batteries are full of it. Your body releases the chemical energy in food to move and grow.

Thermal energy is the energy of particles jiggling about. The hotter something is, the faster its particles move.

Electrical energy is carried by moving electric charges. It powers your phone, lights, and computers. Learn more in electricity basics.

Light energy (radiant energy) travels as waves and lets us see. Sunlight is the source of almost all energy on Earth.

Sound energy travels as vibrations through air, water, or solids, and is what your ears detect.

Energy transfers and transformations

Energy rarely sits still. It is constantly transferred (moved from place to place) and transformed (changed from one form to another).

Trace the energy in a torch:

Chemical (battery) → Electrical (wires) → Light (bulb) + some Thermal (wasted heat)

Or a roller coaster car climbing a hill:

Kinetic (the climb) → Gravitational potential (at the top) → Kinetic (the thrilling drop)

The Law of Conservation of Energy

Here is one of the most important rules in all of physics:

Energy cannot be created or destroyed. It can only be transformed or transferred.

This is the Law of Conservation of Energy. The total amount of energy in a closed system always stays the same.

So why does a bouncing ball get lower each time? The energy is not lost — at every bounce some of it transforms into thermal energy (the ball and floor warm up a tiny bit) and sound energy (the thud you hear). Add it all up and the total is unchanged. Energy that turns into less useful forms like scattered heat is sometimes called dissipated energy.

Try it yourself! 🧪

See energy transform with a simple pendulum.

1. Tie a small weight (a nut or eraser) to a string about 30 cm long.
2. Hold the top still and pull the weight to one side. It now holds gravitational potential energy.
3. Let go. At the bottom of the swing it moves fastest — that is maximum kinetic energy.
4. Watch each swing rise a little lower than the last. Air resistance and friction have transformed some energy into heat and sound.

You have just watched the conservation of energy in action.