NATS 1945 Lecture Notes - Lecture 3: Inverse-Square Law, Orbit, Orbital Speed
31 Oct 2017
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A moving object in a gravitational field has a kinetic energy (ke = 1/2mv2) and gravitational potential energy (ge = gmm/d) In other words, the force of gravity is universal, that it works the same way on earth, space, and any other planet. Space (cid:449)as thought to (cid:271)e the (cid:396)eal(cid:373) of god, (cid:449)h(cid:455) it (cid:271)e(cid:272)a(cid:373)e (cid:272)o(cid:373)(cid:373)o(cid:374) to use (cid:862)the hea(cid:448)e(cid:374)s(cid:863) to describe the sky. The realm of god was imagined to be where things moved in harmonious ways, whereas on earth, natural phenomenon was thought to be completely chaotic, or have complicated explanations. He proved it mathematically, but to justify how this mathematical result could be possible, he offered the following thought experiment. In the thought experiment he said that if you were to fire a cannon ball from the earth, with a relatively low speed. Like 2000 m/s, the ball will follow a curved path and then crush into the ground owing to gravity.
