[qubitcoder]

You can always hold an accelerometer in your hand. If you did so now, assuming you're on Earth's surface, it'd register approximately 9.8m/s/s pointing in the upward direction.

You could also perform one of many historical experiments, such as dropping an object from an elevated height with careful timing, or rolling a round ball down a gently sloped track, and so on.

[marcus_holmes]

Yes, because there is no way of differentiating between acceleration and gravity. Which was my point.