Direct comparison
Potential vs kinetic energy
Potential energy is energy stored because of an object’s position or state; kinetic energy is the energy an object has because it is moving.
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Side-by-side comparison
| Dimension | Potential energy | Kinetic energy |
|---|---|---|
| What it is | Stored energy due to position, shape or state. | Energy due to motion. |
| Depends on | Position in a field, height, or how far something is stretched. | Mass and speed of the object. |
| Object state | Can be stored while the object is at rest. | Only present when the object is moving. |
| Simple formula | Gravitational: PE = mgh (mass × gravity × height). | KE = ½mv² (half × mass × speed squared). |
| Unit | Joule (J). | Joule (J). |
| Everyday example | Water held behind a dam; a drawn bow. | Flowing water; a moving car; a thrown ball. |
| Common types | Gravitational, elastic, chemical, electric. | Translational, rotational, vibrational. |
| Conversion | Converts to kinetic energy when the object is released. | Can convert back to potential energy, e.g. a ball rising. |
| In a pendulum | Greatest at the top of the swing, where it is momentarily still. | Greatest at the bottom, where it moves fastest. |
How one becomes the other
Potential and kinetic energy constantly trade places, and their sum — the mechanical energy — stays constant when no energy is lost to friction. Lift a ball and you store gravitational potential energy; let go and that store converts into kinetic energy as the ball accelerates downward. A swinging pendulum shows the exchange repeatedly: potential energy peaks at the top of each swing and kinetic energy peaks at the bottom. This is the principle of conservation of energy in action.
Common questions
FAQ
Can something have both potential and kinetic energy at once?+
Yes. A moving aeroplane high in the sky has kinetic energy from its motion and gravitational potential energy from its height. A swinging pendulum part-way through its arc holds some of each. The total mechanical energy is simply the sum of the two, and it stays constant if no energy is lost to friction or air resistance.
What is the formula for kinetic energy?+
Kinetic energy is calculated as KE = ½mv², where m is the object’s mass and v is its speed. Because speed is squared, doubling the speed quadruples the kinetic energy. The result is measured in joules when mass is in kilograms and speed in metres per second.
Is gravitational potential energy the only kind?+
No. Gravitational potential energy depends on height, but there are other forms: elastic potential energy stored in a stretched spring or bow, chemical potential energy stored in fuel and food, and electric potential energy stored in charged objects. All are stored energy waiting to be released as another form, often kinetic.
Going deeper
