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Unformatted text preview: 1 Physics 1D03 - Lecture 19 Work and Energy Work and Energy a m F r r = ∑ Energy approach : Net work = increase in kinetic energy- acceleration at any instant is caused by forces- equivalent to Newton’s dynamics- scalars, not vectors - compares energies “before and after” Newton’s approach: “ Work ”: Serway 7.1—7.4 Practice: Chapter 7, Problems 1, 7, 9, 15, 17 Physics 1D03 - Lecture 19 “system” external environment heat flow mechanical work etc. Energy is conserved. Energy must flow into (or out of) a system from the outside universe by various processes. Mechanical work is one way of transferring energy. 2 Physics 1D03 - Lecture 19 Work θ θ Work by a constant force F during a displacement s : s r II F F r F r Units : N • m = joule (J) Work = (component of F parallel to motion) x (distance) We can also write this as This is the “scalar product”, or “dot product”. Work is a scalar . Work = F • s Physics 1D03 - Lecture 19 QUIZ A canoe weighs about 250 N. Your professor picks up the canoe and carries it on his head for 400 m on level ground. canoe and carries it on his head for 400 m on level ground....
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This note was uploaded on 12/14/2010 for the course ENGINEERIN 1D03 taught by Professor N.l.mckay during the Spring '10 term at McMaster University.
- Spring '10