From: chrono.surfer@verizon.net   
      
   > As for the tennis ball, (I wrote also in another response) does   
   > a tennis ball have gravity simply based on its spherical   
   > shape, mass, and density? If true, I suspect measurements   
   > have been taken on such isolated bodies. I would like   
   > to read further on that subject. Any references?   
      
   No. A tennis ball has gravity based on its mass alone.   
      
   Measurements have, in fact, been made on small bodies. I don't know the   
   reference off the top of my head, but the experiment is pretty simple:   
      
   Get three equivalent weights, a tripod, a length of string, and a bar.   
   Attach two of the weights to opposite ends of the bar. Hang the bar from the   
   tripod with the string and balance it. Wait for it to come completely to   
   rest. Place the third weight a short distance away from one of the other two   
   weights. Wait a few days. If the string isn't too springy / resistant to   
   twisting, then the gravity of the two weights will have pulled the together.   
      
   -l.   
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