What do Olympic gymnasts and star-forming clouds have in common?
When Olympic athletes perform dazzling feats of athletic prowess, they are using the same principles of physics that gave birth to stars and planets.
Conservation of angular momentum tells us that when a spinning object changes how its matter is distributed, it changes its rate of spin.
Conservation of angular momentum links the formation of planets in star-forming clouds to the beauty of a gymnast's spinning dismount from the uneven bars.
When athletes hurl themselves into the air to perform a flip, the only force acting on them is gravity. Since gravity only affects their "center of mass," it cannot apply forces in a way that changes the athlete's spin. But the gymnasts can do that for themselves by using the conservation of angular momentum.
By changing how their mass is arranged, gymnasts can change how fast they spin. You can see this in the dismount phase of the uneven bar competitions. When a gymnast comes off the bars and performs a flip by tucking their legs inward, they can quickly increase their rotation rate in midair.
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