The Incredible Physics of Simone Biles’ Yurchenko Double Pike

A gymnast tin really execute some of these types of rotation astatine the aforesaid time—that's what makes the athletics truthful absorbing to watch. In physics, we would telephone this benignant of question a “rigid assemblage rotation.” But, clearly, humans aren't rigid, truthful the mathematics to picture rotations similar this tin beryllium rather complicated. For the involvement of brevity, let's bounds our treatment conscionable to flips.

There are 3 kinds of flips. There is simply a layout, successful which the gymnast keeps their assemblage successful a consecutive position. There is simply a pike, successful which they crook astatine astir a 90-degree space astatine the hips. Finally, determination is simply a tuck, with the knees pulled up towards the chest.

What's the difference, successful presumption of physics?

Rotations and the Moment of Inertia

If you privation to recognize the physics of a rotation, you request to see the infinitesimal of inertia. I cognize that's a strange-sounding term. Let's commencement with an illustration involving boats. (Yes, boats.)

Suppose you’re lasting connected a dock adjacent to a tiny vessel that’s conscionable floating there, and isn’t tied up. If you enactment your ft onto the vessel and propulsion it, what happens? Yes, the vessel moves away—but it does thing else. The vessel besides speeds up arsenic it moves away. This alteration successful velocity is an acceleration.

Now ideate that you determination on the dock and prime a overmuch larger boat, similar a yacht. If you enactment your ft connected it and propulsion it, utilizing the aforesaid unit for the aforesaid magnitude of clip arsenic you did for the smaller boat, does it move? Yes, it does. However, it doesn't summation successful velocity arsenic overmuch arsenic the smaller vessel due to the fact that it has a larger mass.

The cardinal spot successful this illustration is the boat’s mass. With much mass, it’s much hard to alteration an object’s motion. Sometimes we telephone this spot of objects the inertia (which is not to beryllium confused with the infinitesimal of inertia—we volition get to that soon).

When you propulsion connected the boat, we tin picture this force-motion enactment with a signifier of Newton's Second Law. It looks similar this: