Not true. It's an "equal and opposite reaction" thing. If you were to throw rocks in free space, you would propel yourself in the opposite direction to your rock shower. It wouldn't make one bit of difference if the rocks that you threw then hit rocks that you had previously thrown. Dave M. Adam Davis wrote: > Thrust can only be created when you are pushing against something else. _______________________________________________ http://www.piclist.com View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist