Kepler's First Law
I was wondering what makes this law true? Is it simply because planets or stars are orbiting relative to something else that is also orbiting?
Answer
Kepler's laws are really just a consequence of Newton's laws! In other words, they are Newton's laws applied to the case of orbital motion. If you want to see a proof, you will have to take a course in dynamics!
What you would learn is that the inward force of gravity pulls other objects along a trajectory that can be described geometrically. If the energy of the object is high enough, it will travel along a parabolic or hyperbolic curve. But if the energy is low enough, the object will be stuck in an orbit that is either elliptical or circular. In the case of Kepler's first law, the Sun is so massive compared to the planets that the Sun is barely affected by the gravity of the planets.
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Kepler's laws are really just a consequence of Newton's laws! In other words, they are Newton's laws applied to the case of orbital motion. If you want to see a proof, you will have to take a course in dynamics!
What you would learn is that the inward force of gravity pulls other objects along a trajectory that can be described geometrically. If the energy of the object is high enough, it will travel along a parabolic or hyperbolic curve. But if the energy is low enough, the object will be stuck in an orbit that is either elliptical or circular. In the case of Kepler's first law, the Sun is so massive compared to the planets that the Sun is barely affected by the gravity of the planets.