I was trying to help another Blender user with a simple rigid body physics setup. The question he asked was why he couldn’t get two cubes to collide using keyframes. It was a rather vague question so I didn’t wait for more info before I attempted to recreate the problem. I know he was trying this outside the BGE because he said he had set the cubes to Active, which isn’t an option in the BGE.
So, in Blender Render I created a plane for a ground surface and set it to Passive.
I then created two cubes, one at x-5 and one at x+5, and set them to Active with default settings. I then added a keyframe for each at frame 1. Going to frame 20, I moved both cubes to 0,0,0 and set keyframes for both.
When I ran the animation (first resetting the frame to 1), for some reason the cubes did nothing. They didn’t move at all.
I next toggled the Animated checkbox for their physics and ran the animation again. This time, the cubes both moved to the center of the grid and superimposed themselves on the same position without interfering with each other. I didn’t expect that.
Next, I turned off the Animated option for just one cube, and ran the animation. This time, the non-animated cube immediately jumped to the center of the grid while the Animated cube slid as it should across the ground until it hit the other cube and knocked it off the ground plane. This wasn’t expected.
Next, I turned off the Animation option for both cubes again and ran the animation once more. This time the cubes both jumped immediately to the center of the grid and collided. This isn’t what was expected either.
Why is the physics changing how it works with the same settings? Why would the Animation option being turned on and run and then turned off and run change the way objects react?
Here’s the file…