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Topic: Gravity puzzle 


Here is a nice easy one. we all know that gravitational force is reduced proportional to the distance squared. (actually this is not so sure as it seems but we will leave it for another time). Therefore if you have two bodies of mass the closer they are, the bigger the gravitational force (or attraction) between the two. try to find and example where gravity behaves differently  i.e. when the two bodies get closer, the gravitational force between them decreases! Nir 


[quote] try to find and example where gravity behaves differently  i.e. when the two bodies get closer, the gravitational force between them decreases! Nir [/quote] Ugly people? 


Hollow spheres, one inside the other? 


Jonathan you are very close... but if you are inside a hollow sphere you wont feel any gravity at all from the outside !!! but this is the key to the answer... Nir 


Just for kicks, here is the actual formula: k is a constant, m is mass, r is radius: Gravity = (k*m1*m2)/r^2 So imagine the top is 10, and the radius is 1, you get 10, but if the radius is 2, you get 2.5 total gravity... ect ect ect. Btw, did you know that if you took a huge mass, and put a small house sized hole in the middle, and lived in it, time would pass much slower for you than the outside world? You could enter your "home" for 10 years and yet many thousands would have passed for the outside universe. Just something to think about ;) 


So the answer (or one of many) think of a torus (a donut) and another point mass which is on the torus' axis of rotation. when the point of mass is directly in the middle of the torus the gravitational pull it will feel will be zero (due to cancallation of the forces from both sides. when moving a bit along the axis to either side the gravitational pull will increase. N 


I was just coming in here to say 'linking rings'. Nir seems to have it covered though. 