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week5-1

# week5-1 - (Some Sources of Energy Energy Conservation If we...

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(Some) Sources of Energy

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2/7/2011 2 Energy Conservation If we take a closed system, that is one that nothing can enter or leave, then there is a physical law that energy is conserved. We will define various forms of energy and if we examine the system as a function of time, energy may change into different forms but the total is constant. Energy does not have direction just a magnitude and units. Conservation of Energy follows directly from the statement that physical laws do not change as a function of time.
2/7/2011 3 Forms of mechanical energy Kinetic Energy: energy associated with the motion. Potential Energy : energy stored in a compressed spring or stretched elastic or in an object that is held at rest above the earths surface.

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Definition of Work We all need to do some work in order to accomplish something each day. More work is needed to carry 10 pizzas from Pizza Hut to your home than that for 1 pizza. (i.e. larger force is needed with equal distance) . More work is needed to drive yourself from Purdue to LA than that from Purdue to IND. (i.e. same force but longer distance ). Work = Force X distance Unit: 1 joule = 1N X 1m If Force points to the opposite direction of motion, work < 0, i.e. negative work. Otherwise, work > 0, i.e. positive work.
Negative and Positive Work A car skidding to a stop. What force is acting to slow the car?

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week5-1 - (Some Sources of Energy Energy Conservation If we...

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