Behavior of physics different in full speed vs. single step

Is there something I'm missing here. Whenever I use the single frame step in the editor the physics stuff behaves completely differently (more stable).

 

Are you sure you're applying forces / moving / whatever with the physic engine ONLY during FixedUpdate or from trigger forces?

 

I am pretty sure I tried it both ways. I've got it behaving more or less how I want now using FixedUpdate for applying forces. What is the difference in how forces are applied in Update vs FixedUpdate? I assume the only difference is how often the loops run in which the forces are applied. i.e. Forces are applied more often in FixedUpdate vs Update.

Thanks!

 

Update is run every frame. The period between Update's can vary greatly depending on framerate. As far as physics are concerned, when you use a function like AddForce, that function is applied over the duration of the frame - so slower framerates will mean that AddForce(1) will end up making the object go much faster than AddForce(1) on a frame when the framerate is fast. (AddForce takes a Vector3 and that might be reversed, but the point is, it's not reliable.)

The physics engine is updated once at the same time that FixedUpdate is run, and the period between them is constant (I think 0.01 seconds is the default) - i.e. Time.fixedDeltaTime. So an AddForce in FixedUpdate will always apply the same amount of force (and be run the same amount of times per second)