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Phy107Lect6 - From Last Time Newtons three laws of motion 1...

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Fri. Sep 17 Phy107 Lecture 6 From Last Time… Newton’s three laws of motion: 1) Law of inertia 2) F = ma ( or a = F / m ) 3) Action and reaction (forces always come in pairs
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Fri. Sep 17 Phy107 Lecture 6 Question If an apple falls toward the Earth, why doesn’t the moon fall toward the Earth? A. The moon is too big B. The moon is too far away C. The moon does fall toward the earth.
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Fri. Sep 17 Phy107 Lecture 6 Velocity of the moon A B C What is the direction of the Velocity of the moon?
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Fri. Sep 17 Phy107 Lecture 6 Acceleration = change in velocity change in time Velocity at time t 1 Velocity at time t 2 •Speed is same, but direction has changed •Velocity has changed
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Fri. Sep 17 Phy107 Lecture 6 How has the velocity changed? Velocity at time t 1 Velocity at time t 2 V(t 1 ) V(t 2 ) Change in velocity Centripetal acceleration = v 2 / r, directed toward center of orbit. r = radius of orbit
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Fri. Sep 17 Phy107 Lecture 6 Earth’s pull on the moon The moon continually accelerates toward the earth, But because of its orbital velocity, it continually misses the Earth. The orbital speed of the moon is constant, but the direction continually changes. Therefore the velocity changes with time. True for any body in circular motion
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Fri. Sep 17 Phy107 Lecture 6 Experiment F=m 2 g F=m 2 g Acceleration of ball m 1 = F / m 1 = m 2 g/ m 1 m 1 accelerates inward in response to force m 2 g Acceleration = v 2 / r for circular motion
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Fri. Sep 17 Phy107 Lecture 6 Newton’s falling moon • From Newton’s Principia, 1615 Throwing the ball fast enough results in orbital motion
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Fri. Sep 17 Phy107 Lecture 6 Question A 2 newton apple falls from a tree. What is the net force on the apple? 2 newtons downward What is the acceleration? g ~10 m/s 2 downward
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Fri. Sep 17 Phy107 Lecture 6 Question, part 2 I throw the 2 N apple horizontally. After I throw it, what is the net force on the apple?
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