|MadSci Network: Astronomy|
Jr. Redulla, It's all about the mass. To think about how mass comes into play when two objects interact, let's start by analogy. Imagine a train is barreling down the tracks. Now imagine a compact car is racing down the tracks directly toward it. They have a head-on collision. The train may slow down only a tiny bit, but the car is completely stopped and then reverses direction as the train shoves it out of the way. What's the difference between the two? Their masses. Now imagine you have a planet encounter an asteroid. They don't have to actually collide like in the analogy, but simply interact gravitationally. This can be done at quite a distance. Both will exert exactly the same gravitational force on each other, but the planet will have a much larger mass, which will help it resist changes to its motion. It will not be so easily moved from its regular orbit, but the small asteroid will be thrown around like the compact car. ---Bob Macke
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