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Chapter 6. Work, Energy, Power. Work. The work done by force is defined as the product of that force times the parallel distance over which it acts. The unit of work is the newton-meter, called a joule (J) Work is a scalar. q. Work. s cos q. q. Work. F cos q. Energy.

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Presentation Transcript

### Chapter 6

Work, Energy, Power

• The work done by force is defined as the product of that force times the parallel distance over which it acts.

• The unit of work is the newton-meter, called a joule (J)

• Work is a scalar

Work

s cos q

Work

F cos q

• Types of Energy

• Kinetic Energy = “Motion Energy”

• Potential Energy = “Stored Energy”

• Kinetic Energy is the energy possessed by an object because it is in motion.

• Gravitational Potential Energy is the energy possessed by an object because of a gravitational interaction.

Properties of GravitationalPotential Energy

• Arbitrary Zero Point

• You need to select a zero level

• Independent of Path

• All that matters is the vertical height change

• Energy can neither be created nor destroyed, but only transformed from one kind to another.

Works for systems with no losses (friction, air resistance, etc.)

• The amount of kinetic energy transferred to the object is equal to the work done. DKE = W

• Many of the problems can be worked from here

• Determine that energy can be conserved (no losses)

• Pick the zero level for potential energy

• Pick two interesting places in the problem

• Write kinetic and potential energies at these places

• Conserve energy

• (KE + PE)1 = (KE + PE)2

• Power is the time rate of doing work.

• The unit of power is a joule per second, called a Watt (W).