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The Conservation of Energy

The Conservation of Energy. Robert Drach. What do we already Know??. Kinetic Energy: Depends on an objects motion. KE = 1/2 mv 2 Potential Energy: Depends on an object’s position . PE = mgh (gravitational potential energy). What do we already Know?. WORK

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The Conservation of Energy

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  1. The Conservation of Energy Robert Drach

  2. What do we already Know?? • Kinetic Energy: Depends on an objects motion. • KE = 1/2 mv2 • Potential Energy: Depends on an object’s position. • PE = mgh (gravitational potential energy)

  3. What do we already Know? • WORK • Work is done to an object by an external force. • Work is measured in Joules, just like energy! • Where do we go from here?

  4. What is a closed system? • Just what it sounds like! • In a closed system, no energy enters or leaves. • For example: no work is done by an external force.

  5. Conservation of Energy • In closed systems, all energy is conserved. • This includes Potential Energy, and Kinetic Energy. • E = PE + KE • In a closed system, this total E will not change.

  6. Kinetic Energy can take many forms: • Translational KE (1/2 mv2) • Vibrational • Rotational • Potential Energy can also take many forms: • Gravitational Potential • Spring Potential

  7. No matter what type of potential or kinetic energy we use, E is always conserved. • EX: Throwing a ball of mass m. • Immediately after the ball is thrown: • h = 0, --> PE = mgh = 0 • All the energy is kinetic energy.

  8. When the ball reaches the top of its climb: • It temporarily stops, so KE = 0 • It has a height, h, so PE = mgh. h = h v = 0

  9. What happens at the bottom of the fall? • Obviously, it has stopped. • Obviously, it has no height. • So KE + PE = 0 • So what happened to conservation?!? v = 0 h = 0

  10. When the ball hits the ground: • The ground exerts a force on the ball. • The ball and the ground heat up. • The ball makes a THUD. • These are all manifestations of energy. • But since the energy is no longer in the ball, we can no longer say it is conserved!

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