whats a good physics project regarding center of gravity? (Excluding any magnet based models)?

Answer 1

This is a neat one I came across years ago. You can find the center of gravity (CG) of any irregular 2D shape (say something you cut out of a flat piece of cardboard) with a very simple procedure you could almost do blindfolded. Put the cutout on two straightedges held horizontally. Hold the straightedges very steady and level (or rest them on a table) and gradually bring them closer together until they nearly touch. The cutout will stay balanced because if one edge is further from the CG, that edge carries less of the weight of the cutout, so the friction is less and that edge slides closer to the CG. So the two edges will converge to a line passing through the CG. Carefully hold one edge in place and mark that line on the cutout. (This may take a third hand.) Now turn the cutout roughly 90 degrees and repeat. The CG is at (or very near) the intersection point of the two lines, which you can show by balancing the cutout on a small dowel.
Of course you could just find the CG using one straightedge and trial and error, but the idea of "automatic" error correction is more interesting.

Answer 2

Remember the old trick of balancing two forks on the edge of a water glass with a toothpick? If not here's how you do it: 1. Get two dinner forks preferably the same size and style. 2. Get 2 or 3 toothpicks of the round type 2 to 2 and 1/2 inches long. Weave the forks together in a lattice with the toothpick in the center of the lattice with the toothpick sticking out about 1 inch TOWARD the handles of the forks. 3. Fill a 12 to 20 ounce glass with water about 3/4 full. 4. Place the tip of the toothpick on the edge of the glass with the handles of the forks going around the body of the glass. 5. It will take a little bit of practice but you will balance the forks on the edge of the glass because the CENTER OF GRAVITY is at the tip of the toothpick. Hope this helps. Thanks for the 2 points.