Physics

4.12 - Kinetic Energy

6 min

What kinetic energy is

The kinetic energy equation

Worked examples

note 1 of 3

Kinetic energy and what it depends on

Kinetic energy is the energy an object has because it's moving.
A stationary object has none - but a moving car, a falling apple, or a thrown ball all have kinetic energy.
As an object speeds up, it gains kinetic energy; as it slows down, its kinetic energy changes into other forms of energy.

What it depends on

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

note 2 of 3

The kinetic energy formula

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

Where:

$E_{k}$ = Kinetic energy, in joules (J)
$m$ = Mass, in kilograms (kg)
$v$ = Speed, in metres per second (m/s)

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

note 3 of 3

Worked example - Kinetic energy of a car

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

Step 1 - Formula

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

Step 2 - Substitution and calculation

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

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

key terms

TermDefinition

Kinetic energyThe energy an object has because it is moving.

end of notes

Key points to remember

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4.13 - Gravitational Potential EnergyNext up