Why do not you tumble doll overturned ?

Everyone can see the phenomenon: the horizontal brick is very stable, erect it upright, easy to fall; A bottle with half a bottle of water standing on flat ground is very stable, a bottle or a bottle full of water is relatively easy tip over. From the two events mentioned above, it can be seen that for an object to be stable and not easily toppled, two conditions must be met: one is that its bottom area must be large. Second, its weight must try to focus on the lower part; its center of gravity should be low. The object’s focus can be considered the point where the force of gravity placed on it can be applied.

For any object, the larger its bottom area, the lower its center of gravity, the more stable it is, the harder it is to tumble. For example, the pyramid architecture is always underneath the bulge, above the sharp, when loading goods always put heavy things down, light objects on top.
With that knowledge in mind, let’s return to the hasty review. The tumbler’s whole body was very light, but at the bottom of it was a slightly heavy lead or lump of iron, so its focus was very strong. On the other hand, the bottom of the big bulky but round, easy to swing. When the tipping wheel is tilted to one side, the focus and fulcrum are no longer on the perpendicular line because the fulcrum (its contact point and the tabletop) is moved. At that time, under the influence of gravity, the tumbler would swing around the fulcrum until it returned to its normal position. The greater the skewness, the greater the distance

Between the center of gravity and the fulcrum. The greater the swinging effect due to gravity, the more visible the trend will restore it to its original position. Therefore, a tumbler with a bucket cannot tumble.
The phenomenon of objects that are originally standing still, like a tumbling figure, after being subjected to small disturbances that can automatically restore the equilibrium to its original position, in physics, it is called equilibrium. Stable (durable balance). What about spherical objects like table tennis, soccer, volleyball, etc. After being influenced by external forces, it is possible to continue balancing at any position; that kind of state is called a floating balance (floating balance). In an object in equilibrium, the center of gravity and its fulcrum always lie in the same straight line, and the height of the center of gravity never changes. The pen placed horizontally on the table is a kind of floating balance, no matter where it rolls, the focus’s height remains unchanged.