Unfortunately, physics simulations like that are difficult to get stable.
The physics stuff is still perfectly suitable for stuff like moving spaceships around and making them bounce off one another, but when you have a bouncing object resting on the ground like that the tiny changes from frame to frame can cause a simulation to explode unless everything is coded just right.
You could also use the physics to make objects accelerate while they fall but then determine when they have collided with the ground and turn off the physics. That demo there is, by design, a worst case scenario.
The physics stuff is still perfectly suitable for stuff like moving spaceships around and making them bounce off one another, but when you have a bouncing object resting on the ground like that the tiny changes from frame to frame can cause a simulation to explode unless everything is coded just right.
You could also use the physics to make objects accelerate while they fall but then determine when they have collided with the ground and turn off the physics. That demo there is, by design, a worst case scenario.