Gravitational Potential Energy
Energy stored due to height in a gravitational field.
Formula
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Example
A 1 kg book on a 2 m shelf: PE = 1·9.8·2 ≈ 19.6 J.
How it works
Gravitational potential energy is the energy an object has because of its position in a gravitational field, especially when it is raised above the ground. The formula PE = mgh comes from the fact that lifting an object higher requires work against gravity, and the amount of work depends on the object’s mass, the strength of gravity, and how far it is lifted. Near Earth’s surface, g is almost constant, so the energy increases in direct proportion to height.
When to use it
Use this formula when you want to find how much energy an object gains or loses due to a change in height, such as a raised weight, water in a dam, or an object on a shelf. It is also useful in problems involving falling objects, where potential energy can change into kinetic energy.
Worked example, step by step
A 3 kg plant pot is placed on a 1.5 m high ledge. PE = mgh PE = 3 × 9.81 × 1.5 PE = 44.145 J PE ≈ 44.1 J
Common mistakes to avoid
- Using grams instead of kilograms for mass
- Forgetting that height must be measured vertically, not along a slope
- Using the wrong value or units for g, such as 981 instead of 9.81 m/s²
Did You Know?
Gravitational potential energy is why a raised hammer, or water behind a dam, stores usable power.