# Does scaling down 'speed up'? [closed]

A video shows two spherical objects (made up of particles) collide. The title refers to them as two planets colliding. When the objects are indeed as large is planets (however large that might be), the video seems sped up. What if the objects are smaller than that, like the size of marbles? Would they still move as slowly (relatively to each other) as if they were planets?

So, to put it differently, when scaling such a situation down, would they move faster relative to each other? Could the video be showing 'real-time' progression when they would be marbles?

## Updated question

If there are two situations that both have two spherical objects in them that have the exact shape etc. (so both situations only differ in proportion), and you would look at both situations at the same time, would one be progressing quicker than the other?

Disclaimer: I have limited physics knowledge. Please help me improve this question if it is unclear or hard to understand.

## closed as unclear what you're asking by heather, FraSchelle, John Rennie, Jon Custer, WolpertingerNov 1 '16 at 16:16

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• I don't understand the question. I don't see what the initial relative velocities would have to do with the size of the 'planets'. A couple of observations though: The simulation appears to be rendered with the centre of mass in the centre of the frame, hence why things (incorrectly) appear to slow down a bit. If you scaled the planets down to the size of marbles then gravity would no longer dominate and the collision would look very different. – lemon Oct 31 '16 at 14:37
• I tried clarifying my question. Forget the video. I guess the answer is no, as you're saying the gravity 'dominates less' when the size is smaller, which makes the behaviour different the smaller we go. – bzeaman Oct 31 '16 at 14:47
• You updated question still does not make sense. Collisions between 2 planets or between 2 marbles can be fast or slow, regardless of size. – sammy gerbil Oct 31 '16 at 17:46