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Notes on Energy
III
Energy
A. Kinetic Energy – energy of motion measured in Joules (scalar quantity)
1. KE = ½ mv2
2. If the mass is doubled, the KE is doubled
3. If the velocity is doubled, the KE is quadrupled.
B. Gravitational Potential Energy – stored energy due to position of an object.
1. As height above the ground increases (or other arbitrary point), the gravitational
potential energy increases.
2. PE = mgh
3. As an object falls it loses gravitational potential energy.
C. Elastic Potential Energy - is the energy stored in elastic materials as the result of their
stretching or compressing.
1. Examples of elastic materials include springs, rubber bands, arrows drawn into bows.
2. For springs the force applied to the spring (F) is proportional to the displacement of
the spring (x) times the strength of the spring or spring constant (k). F=kx
3. Springs with a predictable behavior follow hooke’s law, stretch them too much they
break.
4. The elastic potential energy stored in a stretched spring is PE = ½ kx2
D. Conservation of Energy – energy is neither created nor destroyed, the sum of the energy
is constant.
1. As an object falls its potential energy is converted into kinetic energy.
2. The potential energy stored in a spring is converted into kinetic energy when the
spring is released.