# Newton - This gives up a way to measure mass Observe the...

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Newton's Law of Gravitation All pairs of objects have attractive gravitational forces acting between them. Gravitational force depends on: mass of both objects o more mass => more force distance between centers of objects o more distance => less force Mathematical form: F = G M M 2  / r 2 where F is the force, G is a constant number, M 1  is the mass of one object, M 2  is the  mass of the other object, and r is the distance between the centers of the two objects. In general: when you see A = B / C A gets bigger as B gets bigger. A gets smaller as C gets bigger. Orbits are stable: The force of gravity is just enough to change the direction of the planet, but not enough  to pull it in. Kepler's Laws can be derived from Newton' Laws. We find that Kepler's 3rd Law also depends on masses.

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Unformatted text preview: This gives up a way to measure mass: Observe the orbital period and distance. Use these to determine mass of planets and moons. CD: You may want to look at the force of gravity animation. • in the 2nd edition Chapter 2 Gallery of the CD (p.1) • in the 3rd edition: under animations in Gravity and Motion (Astronomy Basics) Escape Velocity escape velocity is the speed needed for an object to escape from the force of gravity escape velocity depends on: • mass of the planet (or moon) o more mass => need higher speed to escape • size of planet (or moon) o larger radius => need less speed to escape We will use this later to study the atmospheres of planets and moons....
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## This note was uploaded on 03/09/2012 for the course AST 1002 taught by Professor Emilyhoward during the Spring '10 term at Broward College.

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Newton - This gives up a way to measure mass Observe the...

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