News Link • OLYMPICS London Summer 2012

# Olympic Physics: Diving and the Moment of Inertia

• http://www.wired.com, By Rhett Allain
Let’s look at the 10 meter diving event, in which divers leap from a platform 10 meters above the water. Scoring is based on several factors, including the height and difficulty of the dive, but I will focus only on rotations. Let’s look at how a diver rotates and what matters in a rotation.

Dive Time

How long does a dive from a 10 meter platform last? This isn’t too difficult a question. If we assume the vertical acceleration of the diver is constant, we can use the following kinematic equation:

In this case, I can say the initial y position is 10 meters and the initial y-velocity is 0 m/s (let me say the diver doesn’t jump). The vertical acceleration is 9.8 m/s^2. Solving for the time, I get 1.42 seconds. If you round this a bit, it becomes, “Not very long.” If you want, you could determine the effect an upward jump to start the dive would have. Suffice to say, a 10-meter dive happens pretty quickly.

Angular Momentum

The thing most people don’t realize is once the diver starts to fall, the angular momentum remains essentially constant. What is angular momentum? Maybe we should look at linear momentum, typically called simply “momentum,” first.