## potential energymgh, where m is the object's mass, g is the acceleration
due to gravity, and h is the height above the surface. (This
relationship is true provided that g is constant, which is approximately
true if h is small.) In general, any object that occupies a position in a force field has potential energy. The force field may be gravitational, electrical, or nuclear. In addition, there is elastic potential energy (the stored energy of an object, such as a bow, that is deformed under tension or compression), chemical potential energy, and thermal potential energy. In a coiled spring, the potential energy is proportional to the square of the compression or extension. A copper sphere insuated from electrical leakage can be charged with static electricity (stationary electrons) and the electrical potential energy of the sphere is determined by the amount of static electric charge and the associated voltage. ## Change from potential to kinetic energyThe change from potential energy (due to an object's position) to kinetic energy (due to its movement) and back again occurs with a bouncing ball (A), a ball rolling a hemispherical cup (B) and a swinging pendulum (C). Before a ball is dropped it possesses only potential energy. This is converted to kinetic energy as the ball falls and reaches a maximum at the moment of impact – when potential energy is zero. Potential energy is regained as the ball rises to become stationary again at the top of the bounce. The same sequence of transitions occur in the bob at the end of the pendulum and with the ball rolling in its cup.
## Related category• CLASSICAL MECHANICS | |||||||||

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