Physics : To find the center of mass of various shapes.

The fact that the center of mass of the object is towards the middle tells us that the pull of gravity is focused in the middle of the object. Since the gravity is focused on the center of mass, this means that all of the forces acting upon the body cancel out. Thus creating equilibrium, so if you put your thumb in the center of mass of any shape, the shape is supposed to stay still.

The center of mass of an object depends on its shape. The stability of an object depends on its center of mass. Therefore the stability is dependent on shape. If the shape is supported in this point, forces will balance and give stability to the object. This means that the center of gravity determines the place where the object reaches balanced forces, therefore becoming stable.

Evaluation: This experiment is done with very simple equipment, this is why it has to be very carefully carried out. The center of gravity drawn in some of the shapes is probably misplaced, you can prove this by putting your finger where the point is, and it will most likely not stay balanced and stable. This is not supposed to be happening, that's why when doing the experiment one must make sure that the object is hanging freely from the nail, this way the weight of the shape will displace naturally, helping to draw the lines more accurately. Another thing that may have affected results is the fact that we placed the string apart from the shape and had to push it backwards to measure the line, this could have easily caused an error in measurement. The shape has to be very close to the string to produce more accurate results. Since the shape may have the center of mass outside the paper itself, you have to make sure that you leave not too many empty spaces near the center, and try to make wide shapes rather than thin ones. Another thing needed for this experiment is patience, since the shape may take some time to settle and stop moving. The last thing that I would recommend to get better results is that the more measurements you take from the string and the object the better, since you have more points of reference, which is always a good thing. Isn't it?