PHYSICS 8A-02 (02-2-10)

# PHYSICS 8A-02 (02-2-10) - PHYSICS 8A Professor Joel Fajans...

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PHYSICS 8A Professor Joel Fajans 2/2/10 Lecture 5 ASUC Lecture Notes Online is the only authorized note-taking service at UC Berkeley. Do not share, copy or illegally distribute (electronically or otherwise) these notes. Our student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. LECTURE Today we will begin with a discussion of gravity. So far we have just discussed the gravitational constant, which says that objects fall with an acceleration of 9.8 meters per second squared. But this is only true near the surface of the earth. The gravitational force is very small. For example, let’s calculate the gravitational force between us. Let’s calculate the acceleration. Suppose the 50 kg person were riveted to her chair. How much time would it take for the 60 kg person to get to her? The only reason we feel gravity is because we are near such a massive object, the earth. Why does a piece of paper fall slower than a piece of chalk? If I have some big mass M , and I want to figure out the acceleration of the small mass m from the big mass, I write If I plug in my formula for force, I get Note that this equation does not include the mass of the small mass. So this does not explain the reason the paper falls slower. The reason is air resistance. We can do a vivid demonstration in this tube. In this tube I have a feather and a metal disc. The feather takes much longer than the metal disc to fall. I have a pump here and I can take all the air out of this tube. Now the objects fall at the same speed. What is the gravitational force on the earth? I’ve been using the gravitational constant . Why does this work?

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PHYSICS 8A ASUC Lecture Notes Online: Approved by the UC Board of Regents 2/2/10 D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. 2
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## This note was uploaded on 04/29/2010 for the course PHYSICS 83840p3 taught by Professor Fajans during the Spring '10 term at Berkeley.

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PHYSICS 8A-02 (02-2-10) - PHYSICS 8A Professor Joel Fajans...

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