In prior units, we described motion in terms of position, displacement, velocity, and acceleration as well as the causes of motion by forces and mass (inertia). We focused on a series of mathematical and graphical models of motion using these six physical quantities, which led to the kinematic equations for constant acceleration and Newton's laws of motion. In this segment, we will continue focusing on models and build newer models using relationships between mass and velocity. From these models, we will find that the product of mass and velocity is ==momentum==, and the the product of ==mass and velocity squared== is ==energy==. Both momentum and energy are useful in predicting motion of objects. > [!important] > Both momentum and energy are conserved and involve mass and velocity. Aristotle introduced the term energeia, a term closely related to "work." Thomas Young used the term energy in 1800 but others used the term ==vis viva==, meaning "living force." Energy and work go hand in hand. Most texts begin with work (the action), derive kinetic energy, then introduce potential energy and the law of conservation of mechanical energy. Work is the transfer or exchange of energy while energy is defined as the ability or capacity to do work. This may seem circular at first but has historical context. Work is an action that transfers energy. Currently, physicists state energy is not "stuff" nor is energy a "property." Energy is a basic tenet of nature which is conserved. There are many forms of energy. ### Related Topics --- [[Home|Home]] | [[Energy]] | [[Mechanical Energy]] | [[Kinetic Energy]] | [[Work-Energy Theorem]] | [[Potential Energy]] | [[Law of Conservation of Energy]] | [[Power]]