PHYSICS 8A-08 (03-04-10)

PHYSICS 8A-08 (03-04-10) - PHYSICS 8A Professor Joel Fajans...

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PHYSICS 8A Professor Joel Fajans 3/4/10 Lecture 14 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. ANNOUNCEMENTS The other section had their exam yesterday. It was harder than I had thought it was going to be. The exam I wrote for you is similar. This means the exam is hard and the class average is lower than I expected. The exams are curved, so this doesn’t matter with regards to grades. The class is ranked numerically, and a certain percentage of you will get a certain grade. I realize it is a bit demoralizing however. But realize that if you have a hard time, chances are, so are other people. We will have the exams graded by next Sunday, but I am not guaranteeing that. The two sections will be graded independently because they are given two different exams. We will have a histogram with standard deviations up at some point. We will provide the same formula sheets posted online. You have one 8.5 x 11-inch cheat sheet, and you can keep it for next time. We would like the exam to start at 6:00 p.m. sharp. LECTURE Demonstration : if I were to balance a small bouncy ball on top of a basketball and drop them together, how high will the bouncy ball bounce up? The bouncy ball reaches a height at least twice the distance it was dropped. Let’s calculate what happened. Here is the basketball just before it touches the ground. I draw the bouncy ball as though it is not touching the basketball (in reality it probably is) Now the basketball has touched the ground and the direction of motion has changed. The bouncy ball is still going down. Suppose I have a ball on the basketball. As far as the ant is concerned, what is the velocity of the bouncy ball? The bouncy ball is going down with velocity v and the basketball is going up with velocity v , but that isn’t what the ant sees. The ant sees 2v . This is analogous to standing on a highway watching two cars go in opposite directions, both at the same speed. If the cars are going 60 mph, you would see 120 mph. So as far as this ant is concerned, the ball is approaching with 2 v .
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PHYSICS 8A ASUC Lecture Notes Online: Approved by the UC Board of Regents 3/4/10 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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PHYSICS 8A-08 (03-04-10) - PHYSICS 8A Professor Joel Fajans...

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