Energy Changes

Kinetic Energy (Ek)

Energy of motion; present when something is moving.

Gravitational Potential Energy (Eg)

Stored energy due to height above the ground.

Elastic Energy (Eel)

Stored energy in compressed or stretched objects (like springs or rubber bands).

Thermal Energy (Eth)

Energy released as heat or sound, usually from friction or impact.

Law of Conservation of Energy

Energy can’t be created or destroyed — it just changes form.

Total mechanical energy with no friction

Stays the same (Ek + Eg remains constant).

Effect of friction on energy

Some energy is converted to Eth (heat/sound), so mechanical energy decreases.

Energy pie charts

Represent the percent of each type of energy (Ek, Eg, Eel, Eth) at a moment in time.

Energy pie chart when a ball is held high and not moving

100% Eg.

Energy pie chart when a ball is falling

Some Eg, some Ek (increasing Ek as it falls).

Final energy when a ball hits the ground with friction

100% Eth.

Final energy when a wind-up toy slows down and stops

100% Eth (from friction).

Energy types when a spring launches an object (Start, middle, top)

Start = Eel; Mid = Ek + Eg; Top = Eg.

Energy types when a truck moves at constant speed

Ek (motion) + Eth (friction/air resistance).

How energy changes when a ball is thrown up and caught (no friction)

Ek → Eg → Ek (back to hands), no energy lost.

Why a superball doesn't reach the original height after bouncing

Some energy changed to Eth (heat/sound).

Energy type that increases when something speeds up

Kinetic Energy (Ek).

Energy type that increases when something rises

Gravitational Energy (Eg).

What happens to energy when something stops moving due to friction

It becomes Thermal Energy (Eth).

Does the amount of energy stay the same?

Yes, unless energy is transferred to the environment (as Eth).