Philip M, Allen D Philip -- bang on! Allen -- do you accept Philip's (and my) view? If not, why not? Paul D From Philip M re Alan and Regners figures. On this business of "feeling" acceleration, whilst I do not pretend to having had enough interest in checking the figures, I still reason that its a matter of how forces are applied, as to whether you feel anything. In a suddenly braking car you get flung forward... because the force is at the wheels.. But if the breaking force was applied to every molecule of the vehicle including you, then I concieve no effect to be "felt" Philip. From Allen D Assume for the sake of argument that your body could not detect that change rate, current instrumentation however (acelerometers) are able to detect that amount of inertial change to almost infinite amounts, and they are not "aetheraly" depemdent). Make the switch to the world's best email. Get the new Yahoo!7 Mail now. www.yahoo7.com.au/worldsbestemail