ASTR 3 Lecture Notes - Lecture 6: Ellipse, Wind Wave, Electric Field
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Orbiting is just falling with the right speed. The faster the initial speed is (the force we launch the canon), the farther the cannonball is going to land. Launch into the orbit to rotate the earth: circular velocity of orbit. Launch to escape the earth gravity entirely: the escape velocity. M: the mass of the attracting object, which is the earth in this case. Gravitational acceleration is the same for all objects. a=gm0/r2. Since the astronauts and the spaceship are experiencing the same acceleration, they (cid:28660)r(cid:28664) (cid:28665)r(cid:28664)(cid:28664) (cid:28665)(cid:28660)ll(cid:28668)n(cid:28666) w(cid:28668)t(cid:28667) t(cid:28667)(cid:28664) s(cid:28660)m(cid:28664) mot(cid:28668)on r(cid:28664)l(cid:28660)t(cid:28668)v(cid:28664) to (cid:28664)(cid:28660)(cid:28662)(cid:28667) ot(cid:28667)(cid:28664)r, so t(cid:28667)(cid:28664)y (cid:28663)on"t (cid:28660)pp(cid:28664)(cid:28660)r to move. F=gm1m2/r2: larger distance means less force (cid:28660)n(cid:28663) v(cid:28668)(cid:28662)(cid:28664) v(cid:28664)rs(cid:28660). T(cid:28667)(cid:28664)r(cid:28664)"s (cid:28660) s(cid:28664)p(cid:28660)r(cid:28660)t(cid:28668)on within near objects, which is what is causing tides. Think from the middle perspective: relative to the middle one, the left seems to be moving away and vice versa.
