How do you give physics to an object after an animation?

Question

I'm new to blender. So I was trying to make a simple animation of a cube with physics on it, then I decided to animate the cube to go up in the air and release it to do physics stuff. So the question is, how do you release it?

Answer 1

There is an Animated checkbox in the Rigid Body properties. While it is enabled, the object will not be simulated with rigid body physics but can be animated with keyframes. When the checkbox is disabled, keyframes will no longer be taken into account and the rigid body physics are simulated.

To achieve what you want you can now keyframe the setting of the Animated checkbox. First give the cube some upwards movement with a keyframe animation and enabled checkbox, then disable the checkbox to let the physics take over.

In order to make this work properly, there are a few things to pay attention to:

1. If the Animated checkbox is disabled before frame #4, it will not take the given momentum from the keyframed motion into account.

2. To give the physics some momentum to start from, the last keyframe(s) for the cube motion should not be placed more than one frame before the Animated checkbox is disabled. So if you disable it on frame #10, the last motion keyframes should be at #9 or more, not lower. Otherwise the cube animation is stopped too early and the physics start simulating a motionless object.

3. The first motion keyframes have to be at least 2 frames before the Animated checkbox is turned OFF or the motion will not be taken into account. So if Animated OFF is on frame #10, the first motion keyframes have to be frame #8 or earlier.

4. Generally you have to know, if all animated motion ended before the simulation starts it is not taken into account, and if all animated motion starts after simulation has begun it is not taken into account either.

Some examples

The following will not work because the Animated checkbox is set to OFF at frame #3, which is less than #4 and hence too early:

The next image shows an example where it will work. The Animated checkbox is turned OFF at frame #4, and the last motion keyframes are on frame #3. As long as (OFF frame# - last motion frame#) ≤ 1 it will work (but adding motion keyframes much later in the animation will not be very useful, since the motion will only be taken into account as long as Animated is ON.

The next one is another example for something that's not working. The Animated checkbox is turned OFF at frame #4, but the first motion keyframes are on frame #3 - that's too late to get it working. The distance needs to be (OFF frame# - first motion frame#) > 1.

With what is shown before, the next one doesn't work because the whole keyframed motion ends too early before the simulation starts, so there is no more momentum for the physics simulation. In this case the cube will simply be simulated as if it was motionless at the location where the animation ends.

The last is simply not working because the complete keyframed motion is started after the simulation had already begun: