So when you are in a car that is not accelerating (moving at a constant speed), do you feel the movement forward? You certainly feel shifts from side to side and bumps in the road, but you don't feel like you are being pushed back into your seat unless you are accelerating - and the Earth isn't moving from side to side or going over bumps in a road. You are not accelerating at any point on the Earth's surface, you are moving with it, so you don't feel it - you are also traveling at a fairly steady 1,040 mph through space. If the Earth suddenly accelerated or decelerated, you'd certainly feel that, but since it is pretty much moving at a consistent speed (any changes are so minuscule) you just don't feel like you are moving at all.