PHY183-Lecture20

# PHY183-Lecture20 - Physics for Scientists&Engineers 1 1 Physics for Scientists& Physics for Scientists& Engineers 1 Engineers 1 Spring

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Unformatted text preview: February 20, 2006 Physics for Scientists&Engineers 1 1 Physics for Scientists & Physics for Scientists & Engineers 1 Engineers 1 Spring Semester 2006 Lecture 20 February 20, 2006 Physics for Scientists&Engineers 1 2 Kinetic Energy: Summary Kinetic Energy: Summary Definition: (note: K can never be negative!) Energy unit: Work - Kinetic Energy Theorem: 1 J = 1 kg m 2 s-2 ! K " K # K = W K = 1 2 mv February 20, 2006 Physics for Scientists&Engineers 1 2 Kinetic Energy: Summary Kinetic Energy: Summary Definition: (note: K can never be negative!) Energy unit: Work - Kinetic Energy Theorem: 1 J = 1 kg m 2 s-2 ! K " K # K = W K = 1 2 mv 2 February 20, 2006 Physics for Scientists&Engineers 1 3 Work: Summary Work: Summary Work for constant force - 1d Work for constant force - 3d Work done by a variable force, 1d case Most general 3d case Work done against gravity Work done by spring force W = F ( x ') dx x x ! ' W = r F r r ' ( )• d r r ' r r r r ! W = ! 1 2 kx 2 + 1 2 kx 2 W = r F • ! r r = r F ! r r cos " F ! r W = F ! " x = F ! ( x # x ) W g = mgh February 20, 2006 Physics for Scientists&Engineers 1 4 Power: Summary Power: Summary Definition of power as the rate at which work is done Average power over a time interval Δ t Unit of power (SI) Unit of power (non-SI) Common energy unit Power for constant force P = dW dt P = W ! t 1 W = 1 J/s 1 hp = 550 ft lb/s = 746 W 1 kWh = 3.6 ! 10 6 J = 3.6 MJ P = r F • r v P = Fv cos ! Fv February 20, 2006 Physics for Scientists&Engineers 1 5 Potential Energy Potential Energy Definition: How are work, kinetic energy, and potential energy related? Potential energy, U , is the energy stored in the configuration of a system of objects that exert forces on each other. February 20, 2006 Physics for Scientists&Engineers 1 6 Gravitational Potential Energy Gravitational Potential Energy Definition of gravitational potential energy Change in gravitational potential energy Last week we calculated the work done by the gravitational force on a mass lifted to a height h=y-y : Compare the two results: U g = mgy ! U g " U g ( y ) # U g ( y ) = mg ( y # y ) W g = ! mgh ! U g = " W g February 20, 2006 Physics for Scientists&Engineers 1 7 Energy Storage Energy Storage We do work to lift a mass up to a higher elevation and leave it there, storing the work in form of potential energy...
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## This note was uploaded on 03/19/2008 for the course PHY 183 taught by Professor Wolf during the Spring '08 term at Michigan State University.

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PHY183-Lecture20 - Physics for Scientists&Engineers 1 1 Physics for Scientists& Physics for Scientists& Engineers 1 Engineers 1 Spring

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