Physics

4.21 - Kinetic Energy

6 min

What kinetic energy is

The kinetic energy equation

Worked examples

note 1 of 4

The kinetic energy store

Whenever an object is moving, it has energy in its kinetic energy store.
A stationary object has none - but a moving car, a falling apple, or a thrown ball all have energy in this store.
As an object speeds up, energy is transferred to its kinetic energy store.
As it slows down, energy is transferred away again.

note 2 of 4

Mass - A heavier object has more energy in its kinetic energy store than a lighter one moving at the same speed.
Speed - A faster object has more energy in its kinetic energy store than a slower one of the same mass.

note 3 of 4

$E_{k} = \frac{1}{2} m v^{2}$

The speed is squared but the mass is not, so a change in speed affects the kinetic energy store far more than the same change in mass.

note 4 of 4

A car of mass 1,200 kg is travelling at 18 m/s. Calculate the energy in its kinetic energy store.

$E_{k} = \frac{1}{2} m v^{2}$

$E_{k} = 0.5 \times 1,200 \times 18^{2} = 194,400 J$

So the car has 194,400 J of energy in its kinetic energy store.

key terms

TermDefinition

Kinetic energy storeThe energy store of a moving object.

end of notes

The kinetic energy store

Whenever an object is moving, it has energy in its kinetic energy store.

A stationary object has none - but a moving car, a falling apple, or a thrown ball all have energy in this store.

As an object speeds up, energy is transferred to its kinetic energy store.

As it slows down, energy is transferred away again.