The ground moved beneath his feet and he almost fell.

The friction force depends on how the ground is moving.

It might be that the ground is not moving very fast, he said.

The ground was only a few yards below and moving slowly.

And yet no one around me seemed to notice that the ground beneath them was moving.

If it was possible to reach the most northern point we believe the ground would not move at all.

Did the ground really move or was it his imagination?

This time, he couldn't get to his feet, because the ground was moving.

Then rapidly, as the ground moved and the building cracked, we ran.

"Every time I take a step, the ground moves from under me."