PHY183-Lecture33

# PHY183-Lecture33 - Final Exam Yesterdays Exam An Adobe...

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1 March 27, 2012 Physics for Scientists&Engineers 1 1 Final Exam Our Common Comprehensive Final Exam is on Thursday, May 3 rd from 8:00-10:00PM Location Chemistry (CEM) room 138 Two 8.5 inch by 11 inch sheets of notes (both sides) Calculator Alternate Final Exam University approved excuses only Email me with your reason for taking the exam at the alternate time prior to Friday, April 6 Wednesday, May 2, 7:45 – 9:45 AM (room TBA) March 27, 2012 Physics for Scientists&Engineers 1 2 Yesterday’s Exam An Adobe print error caused some exams to printout incorrectly. Your exam score on the correction exam will be used as your exam 8 score. March 27, 2012 Physics for Scientists&Engineers 1 3 Physics for Scientists & Engineers 1 Spring Semester 2012 Lecture 33 Gravitation March 27, 2012 Physics for Scientists&Engineers 1 4 Gravitation We have been treating the gravitational force only in terms of a constant acceleration g = 9.81 m/s 2 Obviously the gravitational force must be different away from the surface of the Earth We have all seen the pictures from space Here is a picture of astronauts floating over the Hubble Space Telescope NASA launched a repair mission to Hubble on May 11, 2009 Repaired two instruments and installed two new instruments Replaced gyro and batteries and added new thermal insulation The new Wide Field Camera can view in the infrared, which allows viewing deeper into the universe Andrew Feustel and John Grunsfeld work on Hubble March 27, 2012 Physics for Scientists&Engineers 1 5 Gravitational Force The general expression for the magnitude of the gravitation interaction between two masses m 1 and 2 a distance r apart is Newton’s Law of Gravity G is the universal gravitation constant Newton’s Law of Gravity tells us that the strength of the gravitational interaction is proportional to each of the two masses and is inversely proportional to the square of the distance between them F ( r ) = G m 1 m 2 r 2 G = 6.674 10 11 m 3 kg -1 s 2 March 27, 2012 Physics for Scientists&Engineers 1 6 Measuring G G is one of the least accurately known of the physical constants Henry Cavendish (1731-1810) Measured G in 1798 using a torsion balance Cavendish’s measurement was within 1% of the currently accepted value of G

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2 Because the gravitational force is a vector we must specify its direction The gravitational force acting from object 2 on object 1 always points toward object 2 From Newton’s Third Law we know that the force exerted by object 2 on object 1 has the same magnitude and opposite direction to the force exerted by object 1 on object 2 Gravitational Force 3/27/2012 Physics for Scientists&Engineers 1 7 F 2 1 = Fr () ˆ r 21 = r 2 r 1 r 2 r 1 = G m 1 m 2 r 2 r 1 3 r 2 r 1 F 2 1 =− F 1 2 March 27, 2012 Physics for Scientists&Engineers 1 8 Superposition of Gravitational Forces
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PHY183-Lecture33 - Final Exam Yesterdays Exam An Adobe...

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