Work, Energy, Power

WorkThe work done by force is defined

as the product of that force times the parallel distance over which it acts.

dFW The unit of work is the newton-

meter, called a joule (J)Work is a scalar

EnergyTypes of Energy

• Kinetic Energy = “Motion Energy”• Potential Energy = “Stored Energy”

Kinetic EnergyKinetic Energy is the energy

possessed by an object because it is in motion.

221 mvKE

Gravitational Potential Energy

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

mghPEG

Properties of GravitationalPotential EnergyArbitrary Zero Point

You need to select a zero levelIndependent of Path

All that matters is the vertical height change

Conservation of Mechanical EnergyEnergy can neither be created

nor destroyed, but only transformed from one kind to another.

finalinital )PEKE()PEKE(

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. DKE = 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

PowerPower is the time rate of doing work.

Velocity* Force

t

W

Time

Done Work Power Average

Time

cetanDis*Force

Power

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