ASTRON 100 Lecture Notes - Lecture 7: Rail-Gun, Space Elevator, Potential Energy
7 Sep 2016
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Newton: f gravity = g (m1 m2/d^2: g = 6. 67 x 10^-11 m^3/kg/s^2. Why don"t planets just fall into the sun: because they miss, because they have angular momentum. Four steps to determining the sun"s mass: assume circular orbits (a = v^2/r, use newton"s 2nd law (f=ma, use newton"s law of gravitation (f = g msun m/d^2) Equate the forces and solve for the mass. They are falling at the same rate as the space shuttle. To escape the gravitational pull of the earth, you must trade some form of energy for gravitational potential energy: gravitational potential energy: peg = g (me m/d) For a cannon ball to escape earth"s gravitational pull, we must give it kinetic energy: ke = m v^2. Escape velocity is found by equating the two energies so to escape from the surface of the earth the cannon ball must move at 11 km/s. Satellites launched from earth don"t go anywhere near 11 km/s when launched.
