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You can treat anything as a point mass as long as you're far away enough ;) And even with point masses only, orbital mechanics can get quite complex. When you
by iliis 12y ago
You can treat anything as a point mass as long as you're far away enough ;) And even with point masses only, orbital mechanics can get quite complex.
When you are close enough that a significant portion of the comet's mass is "besides" yourself (somewhere off to the side) it will pull you to the side.
This even holds true for spherical objects (say, you standing on earth), where you get gravitational pull not only towards the center but also towards the sides. For a perfectly symmetrical sphere, these sideway forces cancel each other out tough.
But earth isn't a perfect sphere, so even on our own planet you get (very small) variations in gravitational pull (stronger pull at the poles or near mountains (where the crust is thicker)): https://en.wikipedia.org/wiki/Gravity_of_Earth https://en.wikipedia.org/wiki/Gravity_of_Earth
- jessaustin 12y agoI encourage you to think a bit more about what is meant by center of mass. By definition, it takes into account all the mass of the body. If the force of gravity is pulling you "somewhere off to the side", then the center of mass is also "somewhere off to the side". Think about the extreme case of two identical-size, uniform-density spheres attached at a single point. That point will be the center of mass, despite the fact that little of the mass of the entire object is located near there.
- stromgo 12y agoThe center of mass is the point where the force of gravity would pull you if the force increased proportionally with distance. In reality the force decreases as 1/r^2, which changes things. Think about the more extreme case of a barbell -- a single object. If you're 2/3 of the way on the bar, you'll be attracted towards the closest endpoint, away from the center of mass (midpoint).
- jessaustin 12y agoOh! Thanks for the correction; sorry for the noise.