What is Energy in Physics?
In physics, energy is a fundamental quantity that represents the capacity to do work or to transfer heat. It comes in many forms, such as kinetic, potential, thermal, chemical, and electrical. The standard unit for energy is the Joule (J), which is the same unit used for work. This calculator focuses on the two most common forms in classical mechanics: Kinetic Energy and Gravitational Potential Energy.
Kinetic Energy (KE)
Kinetic energy is the energy an object possesses due to its motion. Any object that is moving has kinetic energy. The amount of kinetic energy depends on both the mass of the object and its speed (velocity).
- KE: Kinetic Energy, in Joules (J).
- m: Mass of the object, in kilograms (kg).
- v: Velocity (speed) of the object, in meters per second (m/s).
Notice that velocity is squared in the equation. This means that if you double an object's speed, you quadruple its kinetic energy. This is why high-speed collisions are so much more destructive.
Gravitational Potential Energy (PE)
Potential energy is stored energy an object has due to its position or configuration. Gravitational potential energy (PE) is the energy stored in an object as a result of its vertical position or height in a gravitational field. The higher an object is, the more potential energy it has.
- PE: Potential Energy, in Joules (J).
- m: Mass of the object, in kilograms (kg).
- g: Acceleration due to gravity, in m/s². On Earth, this is approximately 9.8 m/s².
- h: Height of the object, in meters (m), relative to a zero point.
Note that the force of gravity (weight) is `F = mg`. Therefore, potential energy can also be seen as `PE = (Force of Gravity) × Height`.
Conservation of Energy
The Law of Conservation of Energy states that energy cannot be created or destroyed, only converted from one form to another. A simple example is a falling object.
- At the top: A 1 kg ball held 10 meters high has maximum potential energy (`PE = 1kg × 9.8m/s² × 10m = 98 J`) and zero kinetic energy (KE = 0).
- As it falls: The height (h) decreases, so PE is converted into KE. The velocity (v) increases.
- Just before hitting the ground: The height is zero (PE = 0), and all the initial potential energy has been converted into kinetic energy. Its KE is now 98 J, and its velocity would be `v = sqrt(2 × 98 J / 1 kg) ≈ 14 m/s`.
For a deeper dive into these concepts, the Wikipedia article on Energy is a comprehensive resource.