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

Work  s cos 

Work  F cos 

Energy  Types of Energy Kinetic Energy = “Motion Energy” Potential Energy = “Stored Energy”

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

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

Properties of Gravitational Potential Energy  Arbitrary Zero Point  You need to select a zero level  Independent of Path  All that matters is the vertical height change

Conservation of Mechanical Energy  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.)

Work Energy Theorem  The amount of kinetic energy transferred to the object is equal to the work done.  KE = W  Many of the problems can be worked from here

Problem Solution Guidelines  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  Power is the time rate of doing work.

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

On to problems...