Lecture 15

# Lecture 15 - Lecture 15 pls-15.1 Potential Energy and...

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Lecture 15 pls-15.1 Potential Energy and Conservative Forces Media: 1. Box 2. Tennis Ball 3. Steel Balls and Paper 4. Happy and Sad Balls 1. Potential Energy Let’s compare the motion associated with two forces: (i) Friction Friction takes energy away from the box. Clicker questions 1 and 2 . (ii) Gravity i v r k f r 0 = f v r 2 2 1 i i mv KE = 0 = f KE 1 v r g r m At some height 0 2 = v 2 1 1 2 1 mv KE =

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Lecture 15 pls-15.2 Gravity takes KE away, but the KE returns when ball returns to its initial height. For gravity, we say that the KE went somewhere and that it has the potential to return. We thus refer to this missing KE as potential energy (PE). 2. Gravitational Potential Energy PE associated with the gravitational force is know as gravitational PE (GPE). We can define GPE by considering constant-acceleration motion with g a y = . One of the 4 kinematics equations is () 1 2 2 1 2 2 2 y y a v v y + = Let’s multiply this equation by m 2 1 and use the fact that g a y = . Then
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## This note was uploaded on 03/26/2012 for the course PHY 1020 taught by Professor Kodera during the Fall '11 term at University of Florida.

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Lecture 15 - Lecture 15 pls-15.1 Potential Energy and...

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