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7.2 Energy

7.2 Energy. What is Energy?. Energy is the ability to do work. It measures the ability for things to move or cause a change in matter. Examples: changes in temperature, speed, position, pressure, or any other physical variable. Some Forms of Energy. Units of Energy.

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7.2 Energy

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  1. 7.2 Energy

  2. What is Energy? Energy is the ability to do work. It measures the ability for things to move or cause a change in matter Examples: changes in temperature, speed, position, pressure, or any other physical variable.

  3. Some Forms of Energy

  4. Units of Energy Pushing a 1 kilogram object with a force of one newton for a distance of one meter uses one joule of energy. 1 J = 1 N•m

  5. Potential Energy Potential energy: energy due to position. Usually due to height! Think of as “potential to fall” Highest EP Lowest EP

  6. Potential Energy EP = mgh gravity (9.8 m/sec2)

  7. Potential Energy Example What is the potential energy of a 4 kg cat crouched in a tree 3 m off the ground?

  8. Potential Energy Example What is the potential energy of a 10kg baseball that is 2m off the ground?

  9. Kinetic Energy Kinetic energy: energy due to motion The kinetic energy equals the work the object can do by exerting force as it stops.

  10. Kinetic Energy Example What is the kinetic energy of a 10 kg dog running at 5 m/s?

  11. Kinetic Energy Example What is the velocity of a 50 kg pterodactyl flying with a kinetic energy of 90,000 J?

  12. 7.2 Conservation of Energy

  13. Energy Flow Kinetic energy can be converted into potential energy and vice versa.

  14. Conservation of Energy • The Law of Conservation of Energy says that energy cannot be created/destroyed, just changed. Total energy before = total energy after

  15. Conservation of Energy Example When you throw a ball in the air, the energy transforms from kinetic to potential and then back to kinetic.

  16. Conservation of Energy Example A 0.5 kg ball moving at a speed of 3 m/s rolls up a hill. How high does the ball roll before it stops?

  17. Conservation of Energy Example A 800kg roller coaster cart is at the top peak of Valley Fair’s Wild Thing (60m drop!). At the bottom of the drop, what will its velocity be? (assume all energy is converted to kinetic energy)

  18. Potential & Kinetic Energy Example A 2 kg rock is at the edge of a cliff 20 meters above a lake. The rock becomes loose and falls toward the water below. What is the potential energy and the kinetic energy of the rock at the top of the hill and when it is halfway down? Its speed is 14 m/s at the halfway point. Potential (top) = Potential (halfway) = Kinetic (top) = Kinetic (halfway) =

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