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Work, Power, and Modes of Energy

Work, Power, and Modes of Energy. Work. Scalar quantity defined as the product of the force applied to an object and the displacement of the object. W= Fd. Units for work is Joules J= N·m. If work is scalar, can it be negative?.

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Work, Power, and Modes of Energy

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  1. Work, Power, and Modes of Energy

  2. Work • Scalar quantity defined as the product of the force applied to an object and the displacement of the object. • W=Fd Units for work is Joules J=N·m If work is scalar, can it be negative? Yes, if the Force acting on the object is in the opposite direction of the object’s motion then work will be negative.

  3. Identify the following as work/non-work. A book falls off a table and free falls to the ground. A teacher pushing on a brick wall. A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. (Careful!) A rocket accelerates through space.

  4. Calculating Work • A 10-N force is applied to push a block across a friction free surface for a displacement of 5.0 m to the right. W=Fd W=(10N)(5.0m) W=50J A force of 50 N acts on the block to move the block a horizontal distance of 3.0 m. How much work is done by the applied force?

  5. Graphing Work Force vs Displacement L x W = 2 m x 25 N = 50 N·m = 50 J • If a 25 N force is applied to an object for 2 meters, how much work is done on the object? • W = Fd = • (25N)(2m) = • 50 J • What is the area under the graph at right?

  6. Power • The rate at which work is done. (Work/Time) • P=W/t • P=(Fd)/t • P=Fv Metric unit for power is Watts Watts = J/s (1000 Watts = 1 kW) English unit for power is horsepower (Hp) 1 Hp=746 W Two physics students, Will N. Andable and Ben Pumpiniron, are in the weightlifting room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the 100-pound barbell over his head 10 times in 10 seconds. Which student does the most work?

  7. What is Energy (E)? • The ability to do work in a system. • Changes in: • Temperature • Motion • Shape System: object(s) we focus on in a problem. Surroundings: everything else! Energy is kinda like a substance: You can measure it. (Joules, calories, BTUs) It can be stored in a variety of ways. It can be transferred. It is universal.

  8. Kinetic Energy (K) • “moving” energy • Anything in motion has KE • Wind • Rain • Cars • People • Dependent on m and v • But….velocity has more of an effect than mass.

  9. Potential Energy (U) • Energy because of position. • Several Types: Gravitational Potential Energy (UG) Energy due to Fg. Comes from mass, height, and g. The higher off the ground, the more UG. No height, No UG. Elastic Potential Energy (US) Energy due to stretching or compression. Often transferred to other objects causing them to move.

  10. Chemical Potential Energy • Energy stored in the chemical bonds of atoms. • Food • Batteries • Wood • Fuel • If it can undergo a chemical change then it has PEchem

  11. Dissipated Energy • Energy that produces random movement of molecules, light, or sound. • Usually due to friction or deformation of objects. • Non-reusable form of energy. Where does all that energy go?

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