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Why does the ball appear to bounce before it hits the floor? 11 months 1 week ago #593

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Simulating a ball bouncing off the floor caused the ball to bounce before it hit the floor - what is going on?

If you can't see the ball touching the floor before it bounced, this is because the impact has probably happened in the middle of your frame time. If you sample your time with a step of 1 second and your ball hits the floor at time 10.5,  then the impact with the floor happens between frame 10 and frame 11. So at frame 10, your ball was above the ground. If your impact restitutes 100% of the momentum, then the ball would be at the same height at frame 11. But if you have 10 substeps and you could watch them, then you would see the ball hit the floor at frame 10 subframe 5.
Also, you should verify (using the Guide Geometry / Physics Draw) that you have not accidentally set a large Outer Fatness for the ball or ground. Keep in mind that while your floor might be just a thin grid mesh, the collision surface is a 3D volume, i.e. the mesh extruded along the normal by Outer Fatness. So if the Outer Fatness is very large, and you are not displaying the collision surface with the Guide Geometry / Physics Draw, then it can seem like the ball bounced way too early.

Here for example I am using the Carbon Guide Geometry / Physics Draw to visualize the actual collision surfaces. 
This is the surface of the mesh plus any Fatness (Thickness) that has been added. You can see the the ball and floor surfaces are meeting correctly.

But if we just look at only the geometry then there is an apparent gap between the ball and the floor.

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Last edit: by Sebastian.
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