Lecture 7 to web

# Lecture 7 to web - Chapter 6 Energy and Oscillations Today:...

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Chapter 6 – Energy and Oscillations Today : Hand in homework #3 Wednesday Physics 110 Help : Physics 110 Discussion Session – Tuesdays 7 – 9 PM, YKK220-001 Alternatives – 1) tonight 6 – 9 PM by appointment contact: [email protected] 2) General physics study hall 8-12 Tuesday nights in Silliman Dining Hall Today’s Topics : Complete Chap 6 Potential Energy Simple Harmonic Motion Start Chap 7 Momentum and Impulse Momentum Conservation

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Work, Energy, Kinetic Energy – Last Class Energy = Capacity to do work i.e.) Release of energy does work. Doing work on something adds energy to it. equivalent ENERGY WORK E = W = F x d E = W = F x d Kinetic Energy example: Throw a ball Exert a force (F) over a distance (d) Ball acquires kinetic energy (energy of motion) KE = 1/2 mv KE = 1/2 mv 2 m = mass v = velocity Derivation: (since F = ma) KE = W = F x d = m a d (since d = 1/2 at 2 ) KE = m a ( 1/2 at 2 ) = 1/2 m (at) 2 (since v = at) KE = 1/2 mv 2
Lift an object of mass M to height h. W = F x d = (mg) x h = mgh Object in hand, no velocity, but has an added energy due to earth’s gravitational field: Potential Energy Potential Energy P.E. = mgh P.E. = mgh Can get back real energy drop object! As object falls it accelerates, speeds up PE is converted to KE ! At impact with ground : PE = 0 KE = 1/2 mv 2 = mgh Velocity on impact v = (2gh) Potential Energy due to Gravity

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Potential Energy Potential Energy is stored energy associated with the object’s position (rather than its motion) can be released into kinetic energy of motion is due to conservative forces (gravity, spring force) Conservative Force You can always get the energy back e.g.) gravity, elastic forces Elastic Force results from stretching or compressing an object. (compress springs, stretch bands)
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## This note was uploaded on 04/07/2008 for the course PHYS 110 taught by Professor Johnharris during the Spring '08 term at Yale.

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Lecture 7 to web - Chapter 6 Energy and Oscillations Today:...

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