What is Gravitational Potential Energy?
Imagine lifting your backpack off the floor and placing it on a high shelf. You did work to lift it — and now that backpack has something it didn't have before: stored energy that could be released if it fell back down. This stored energy is called gravitational potential energy.
The energy stored by an object due to its position in a gravitational field. The higher an object is above a reference point, the more gravitational potential energy it possesses.
GPE is a form of potential energy — meaning it is stored and has the potential to be converted into other forms of energy (like kinetic energy) when the object is allowed to fall.
Think of GPE like money in a savings account. When you lift an object, you're "depositing" energy into it. When the object falls, it "spends" that energy — converting it into movement (kinetic energy).
Key points to understand from the start:
- GPE depends on how high the object is above a chosen reference level
- GPE depends on the mass of the object
- GPE depends on the gravitational field strength of the planet or body you're on
The GPE Formula
We can calculate gravitational potential energy using a straightforward formula:
Where:
- = gravitational potential energy, measured in joules (J)
- = mass of the object, measured in kilograms (kg)
- = gravitational field strength, measured in newtons per kilogram (N/kg)
- = height above the reference level, measured in metres (m)
The force exerted by gravity on each kilogram of mass. On Earth's surface, (more precisely 9.8 N/kg, but 10 N/kg is used in most MYP calculations).
The value of changes depending on where you are. On the Moon, , which is why astronauts feel much lighter there. On Jupiter, .
The unit analysis confirms our formula makes sense:
Since a newton-metre equals a joule, the units work out perfectly.
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