Hi, I've been reading Vic. Stenger's book "The comprehensible Cosmos" and have a question about the example he gives for Galilean invariance. In his example, Galileo drops a weight from the tower of Pisa and to a person standing near the tower (and thus in the same inertial? frame of the tower) the weight falls in a straight line. For an observer moving at velocity on a river near the tower, the weight falls in a parabolic shape. I can't visualize this. I've been on boats and watched things move on land and can't say I've noticed anything like what Stenger talks of. I'm not even sure how it relates to Galilean invariance. The diagram in Stenger's book doesn't really help. I'm probably asking a total noob question, but if anybody could help or point me to a better description or diagrams that'd be great. Thanks in advance. P.S. I did a search for Galilean invariance before posting but didn't find anything that appeared relevant. Hopefully I haven't done anything flame-worthy.