Energy and Motion I

Energy is the ability to make things happen. Modern science talks about it as being in different stores:

• Kinetic — anything that's moving.
• Gravitational potential — anything raised in a gravitational field.
• Elastic potential — stretched or compressed springs and bands.
• Chemical — food, fuel, batteries.
• Thermal (internal) — total energy of all the vibrating particles in a substance.
• Nuclear — stored in atomic nuclei (released in fission and fusion).
• Magnetic — between magnets or in coils.
• Electrostatic — between charged objects.

Examples:

• A skier at the top of a hill — gravitational potential.
• A speeding car — kinetic.
• A stretched bow — elastic potential.
• A bowl of pasta — chemical.
• A hot cup of tea — thermal.

Energy moves between stores by FOUR transfer pathways:

1. Mechanically — a force moves through a distance (pushing, lifting, pulling).
2. Electrically — current flows in a circuit, transferring energy from a battery or supply to components.
3. By heating — energy moves from hot to cold by conduction, convection or radiation.
4. By radiation — light, infrared, microwaves, sound waves carry energy.

A familiar example: kettle boiling water.

• Energy starts in CHEMICAL store of the power station's fuel.
• Transferred ELECTRICALLY to your house.
• Transferred ELECTRICALLY again into the kettle's heating element.
• Transferred BY HEATING from the element to the water — increasing the water's THERMAL store.
• Some heat also radiates from the kettle's surface — transferred BY RADIATION to the surroundings.

Conservation of energy is one of the most important laws in science:

The total energy in a closed system stays the same. Energy is never created or destroyed — only transferred between stores.

When we say energy is 'wasted', we don't mean it's destroyed. It's transferred to a less useful store — usually thermal (heat dissipated to the surroundings).

A bouncing ball example:

• At the top of its bounce: all GRAVITATIONAL POTENTIAL.
• On the way down: GRAVITATIONAL POTENTIAL → KINETIC (speeding up).
• At impact: KINETIC → momentarily ELASTIC POTENTIAL (squashed ball) and SOUND + THERMAL (warmth in the ball and floor).
• Back up: ELASTIC POTENTIAL → KINETIC → GRAVITATIONAL POTENTIAL — but less than before, because some has gone to thermal/sound.

Eventually all the original gravitational potential ends up as thermal energy spread to the surroundings — the energy is still THERE, just in a much less useful form.