ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions. ***************************************************************************** Appropriately enough for Birkat Hakhama.... -----Original Message----- From: Tim Pula Sent: Wednesday, April 08, 2009 11:52 AM Gravity bends space - Set up a sheet of neoprene or latex, pulled taught, on a frame. Use a dense metal sphere as a planet or star. Place it on the neoprene to warp space. Release a marble (space ship or comet) from one side of the frame and watch the warping of space affects its travel. It is a home made gravity well of sorts. -------------------- OK, I've seen this model many times, and I partly grok it, but there's one thing I just don't get, and have never been able to find out: The model above is supposed to show how gravity is caused by space getting warped by mass; the more massive, the bigger the warp, ergo stars + planets have a stronger gravitational pull than less massive objects. So far, so good. But in the model Tim describes, if you have some object like a bowling ball representing earth, and a marble or something representing a person (not to scale, obviously) --- why does the marble roll >towards< the bowling ball? Well, gravity. But even if space curves towards the planet/other massive object, why does a less massive object roll 'downhill' towards the more massive one? Why not go 'uphill' on the curve, away from the gravity well? In other words, why is gravity an attractive force? Other forces can be repulsive ones, how come gravity isn't? This always bugs me when I see these kinds of models. Stupid gravity - something oughta be done about! Jonah Cohen Outreach & Public Programs Manager The Children's Museum *********************************************************************** For information about the Association of Science-Technology Centers and the Informal Science Education Network please visit www.astc.org. Check out the latest case studies and reviews on ExhibitFiles at www.exhibitfiles.org. The ISEN-ASTC-L email list is powered by LISTSERVR software from L-Soft. To learn more, visit http://www.lsoft.com/LISTSERV-powered.html. To remove your e-mail address from the ISEN-ASTC-L list, send the message SIGNOFF ISEN-ASTC-L in the BODY of a message to [log in to unmask]