S3.1 Introduction
[A] What is energy?
- Energy is a scalar quantity associated with the state
of a system; work is associated with changes in that state. The
ideas of work and energy provide a new angle from which to view
Newtonian mechanics, and a powerful set of tools for solving problems.
Key Point 3.1
Energy is defined as the ability of a system to do work. Energy can come in two forms–
.... kinetic
Key Point 3.2
Kinetic energy is the energy a body has by virtue of its motion....and potential
Key Point 3.3
Potential energy is the energy a system stores as a result of its state, shape or position.Examples
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Examples
- A high speed train has kinetic energy
- The water in a hilltop reservoir has gravitational potential energy
- A compressed spring has elastic potential energy
- A rotating bicycle wheel has rotational kinetic energy
- A container of natural gas has kinetic and potential energy
Is that clear?
A container of gas has both kinetic and potential energy; the kinetic energy comes from the motion of the atoms or molecules that the gas is made of, whereas the potential energy is in the form of chemical potential energy, as a result of bonds or interactions between the atoms / molecules- The concepts of energy and energy conservation, although consistent with Newtonian mechanics, are valid in regimes and for systems where Newtonian mechanics does not hold; at those extreme speeds and tiny distances where relativity and quantum mechanics reign.