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How It Works
Gravitational potential energy (E = mgh) is the energy stored in an object because of its height above a reference point. The higher or heavier the object, the more potential energy it has. When released, this energy converts to kinetic energy as the object falls. Standard gravity on Earth is 9.80665 m/s².
Example Problem
A 10 kg rock sits on a cliff 30 m above the ground. How much potential energy does it have?
- E = 10 × 9.81 × 30 = 2,943 J
If the rock falls, all 2,943 J converts to kinetic energy just before impact (ignoring air resistance).
Frequently Asked Questions
What is the reference point for potential energy?
You choose the reference point (where h = 0). Common choices are the ground, the floor, or the lowest point in the problem. Only differences in potential energy matter physically.
How do potential and kinetic energy relate?
In a closed system, the total mechanical energy (KE + PE) is conserved. As an object falls, potential energy converts to kinetic energy. At the top of its arc a thrown ball has maximum PE; at the bottom it has maximum KE.
Can potential energy be negative?
Yes, if the object is below your chosen reference point. For example, a ball in a valley with the hilltop as reference has negative potential energy. The sign depends on the reference you pick.
Related Calculators
- Kinetic Energy Calculator — find energy of motion (½mv²).
- Work Calculator — calculate work done by gravity or other forces.
- Gravity Equations Calculator — determine g at different locations.
- Projectile Motion Calculator — trace a projectile where PE converts to KE.
- Energy Unit Converter — convert between joules, calories, and BTU.
Reference: Lindeburg, Michael R. 1992. Engineer In Training Reference Manual. Professional Publication, Inc. 8th Edition.