Why don't people fall off when the earth travels at 100000 kilometers per hour through space?

Answer 1

First of all, the speed isn't nearly such a dramatic number. The highest rotational speed of any point on

the earth's surface is at any point on the equator, which spins at about 1,675 kilometers per hour.

The answer to the question is that the gravitational attraction between you and the earth is greater than

the apparent 'force' trying to throw you off. (How much greater ? That's your weight.)

Answer 2

The middle of the earth is the "Center of Gravity". Which is kind of like a magnet. That is why if we jump, we come back down.

If there was no Center of Gravity, if we jump we wouldn't land back on the floor.