# What Is Energy

1. What is energy?

2. Differentiate Potential from Kinetic Energy

3. Differentiate Gravitational Potential Energy from Elastic Potential Energy 1. In physics, energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems. However, this must be understood as an overly simplified definition, as the laws of thermodynamics demonstrate that not all energy can perform work. 2. Kinetic energy is the energy something has because it is moving. Potential energy is the energy something has because of its position or configuration. 3. Gravitational energy is the potential energy associated with gravitational force. If an object falls from one point to another point inside a gravitational field, the force of gravity will do positive work on the object, and the gravitational potential energy will decrease by the same amount.

When accounting only for mass, gravity, and altitude, the equation is: U = mgh

where U is the potential energy of the object relative to its being on the Earth's surface, m is the mass of the object, g is the acceleration due to gravity, and h is the altitude of the object. If m is expressed in kilograms, g in meters per second squared and h in meters then U will be calculated in joules.

Elastic potential energy is the potential energy of an elastic object (for example a bow or a catapult) that is deformed under tension or compression (or stressed in formal terminology). It arises as a consequence of a force that tries to restore the object to its original shape, which is most often the electromagnetic force between the atoms and molecules that constitute the object.

The elastic potential energy stored in a stretched spring can be calculated by finding the work necessary to stretch the spring a distance x from its un-stretched length. an ideal spring will follow Hooke's Law:

F = -kx ; where F = restoring force, k = spring...

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