Lect05-Phys172s10-(3.1-3.5-Fundamental_forces)

Lect05-Phys172s10-(3.1-3.5-Fundamental_forces) - 1 Spring...

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Unformatted text preview: 1 Spring 2010 PHYS 172: Modern Mechanics Lecture 5 Fundamental Forces Read 3.1 3.5 The Four Fundamental Forces Composite forces like the spring force, air drag, friction, etc. are combinations of these four fundamental forces 2 Newtons Great Insight: The force that attracts things toward the earth (e.g. a falling apple) is the same force that keeps planets orbiting about the sun Question: Why doesnt the Moon fall into the Earth? The gravitational force law 2 1 on2by1 2 1 2 2 1 grav m m F G r r-- = - & & m 1 m 2 2 1 r- & 2 1 r- Newton 2 1 2 1 r r r- - & & & m 1 m 2 2 r & 1 r & 2 11 2 Nm 6.7 10 kg G- = Cavendish Gravitational constant 3 Features of gravitational force 2 1 on 2by1 2 1 2 2 1 grav m m F G r r-- = - & gravity is always attractive 2 1 on 2by1 2 1 2 2 1 grav m m F G r r-- = - & gravity is an inverse square law 2 1 on 2by1 2 1 2 2 1 grav m m F G r r-- = - & the force depends upon the product of the masses Distance between two objects Point object: idealized object which has no size, all mass is in one point If distance between the two objects is >> than their size, can model the objects as point-masses Real objects: have size Special case: spherical objects (spherical symmetry)...
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This note was uploaded on 02/07/2010 for the course PHYS 17200 taught by Professor Gaboracsathy during the Spring '09 term at Purdue University-West Lafayette.

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Lect05-Phys172s10-(3.1-3.5-Fundamental_forces) - 1 Spring...

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