# Help Zone

### Student Question

Secondary V • 2yr.

What is the difference between potential energy and kinetic energy?

Physics

## Explanations (1)

• Explanation from Alloprof

Explanation from Alloprof

This Explanation was submitted by a member of the Alloprof team.

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Team Alloprof • 2yr.

Potential energy is defined as the energy that an object possesses due to its position or shape. For example, a stationary ball on top of a hill has a lot of potential energy, since it has the potential to roll down the hill.

Kinetic energy is defined as the energy that an object possesses due to its movement. For example, a ball rolling down a hill has a lot of kinetic energy due to its rolling motion.

Two caveats are worth mentioning:

• Objects can have both kinetic energy and potential energy at the same time. For example, a roller coaster rolling down a slope has kinetic energy because of its movement, but also potential energy because it has not yet exhausted its potential to descend the hill.

• Objects can transform their potential energy into kinetic energy and vice versa. To take the example of the roller coaster, it can transform its gravitational potential energy into kinetic energy on the way down.

The potential energy is described according to the following equation:

$$E_{p} = m • g • ∆y$$

Legend:

• Ep: potential energy (J)

• m: mass (kg)

• g: gravitational acceleration constant (= 9.81 m / s ^ 2)

• ∆y: variation of the height of the object

The kinetic energy is described according to the following equation:

$$E_{k}= \frac{1}{2} • m • v^{2}$$

Legend:

• Ek: kinetic energy (J)

• m: mass (kg)

• v: speed (m / s)

We can see that the two forms of energy depend on the mass of the object. So, for example, a heavier object that goes at the same speed as a lighter object will always have more energy. Likewise, a heavier object at the same height as a lighter object will always possess more energy.

We also note that the expression of kinetic energy depends on the speed of the object and that the expression of potential energy depends on the height of the object.

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