Physics of a Back Flip

Being a cheerleader and ex gymnast I am constantly asked, "Can you do a back flip?" and the answer is always yes. People always wonder how to do one and if I could teach them. When explaining how to do it, it sounds pretty simple. Jump, keep arms up, tuck your knees at the top, and flip over. But there is much more to it than that.

Back flips defy the laws of gravity. You need the right amount of momentum to rotate before gravity pulls you down.

Now this diagram does not have good technique but it gets the point across

According to the law of conservation of momentum, you cannot gain momentum mid air. The initial jump gives the tumbler the momentum they need.You can also gain extra momentum by using your core to tuck you knees to your chest faster. Without the correct about of momentum the person will most likely fall or not land right. (See below video)

Angular momentum (L) = rotational velocity(w) * moment or inertia of center of mass (I)

When the person goes into the "tuck" position, it makes the moment of inertia smaller and the rotational velocity larger. This makes sense since it is much easier to do a standing back tuck than a standing back layout (person flat/ straight when flipping). Tucking makes the rotation faster allowing you more time to find your landing. 

So here are some helpful tips to doing a back flip

1. Jump as high as you can
2. Use your core and tuck your knees as tightly to your chest as possible
3. If needed use your arms to pull your legs in to help you rotate

Good luck and happy flipping!