Lecture 9

# Lecture 9 - Lecture 9 pls-9.1 Physical Forces - Gravity and...

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Lecture 9 pls-9.1 Physical Forces - Gravity and Contact Forces Media: 1. tennis and ping pong ball 2. box 1. Gravity Clicker questions 1 and 2 . For an object in freefall g a r r = . N’s 2nd law is net m F a r r 1 = , so if g net F F r r = , N’s 2nd tells us g m F g r r 1 = Æ g F r r m g = (near the surface of the earth). 2. Contact Forces 3 types: normal, friction, tension – macroscopic terms Contact forces arise from microscopic electrostatic forces between atoms comprising the two objects in contact. E.g., box sitting on a table. Electrostatic repulsion between electrons in surface atoms of each object. Lots of microscopic forces, but to keep things simple we imagine that we sum these microscopic forces (on a given object) and talk about table box

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Lecture 9 pls-9.2 their sum as 1 macroscopic force (or perhaps 2 macroscopic forces) on the object. 3. Normal Force —A force that is normal (perpendicular) to the surface between the two objects. Example 1
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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 9 - Lecture 9 pls-9.1 Physical Forces - Gravity and...

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