http://www.ck12.org Chapter 6. Work and Energy
6.3 Energy Conservation
Objectives
- Understand the meaning of energy conservation
- Be able to use energy conservation in solving problems.
Vocabulary
- Conservation of Mechanical Energy:The total of kinetic energy and potential energy in a system remains
constant as long as there are no dissipative forces or interaction with outside the system. - Conservation Principle:A conserved quantity is a quantity where the total cannot increase or decrease.
- dissipative forces:Forces such as friction that change mechanical energy into other types of energy, such as
heat energy.
Introduction
In the language of physics, a conserved quantity is a quantity where the total can never increase or decrease. Conser-
vation of energy means that energy is transformed from one type to another, but is never added or removed. Consider
climbing up to the top of a half-pipe at a skate park.
FIGURE 6.16
Climbing up the ladder in a skate park.By climbing up a ladder, a person is adding in mechanical energy. There is chemical potential energy within
their body that is expended by using their muscles. In physics terms, they do work climbing to the top of the
half-pipe. This creates gravitational potential energy.
Suppose the half-pipe is 4 meters tall and the person has a weight(mg)of 900 Newtons. This means that there is
(900N)(4m) =3600J of gravitational potential energy created by climbing up.
If the person skates off the edge, they are lowering their height (reducing potential energy) but also speeding up
(gaining kinetic energy). This is a basic energy transformation and illustrates the principle ofConservation of