A Tennis Racket TheoremEvan LeeAward: Top 100
School: albany high school The intermediate axis theorem (also known as the tennis-racket theorem or the Dzhanibekov effect) states that when an object has three distinct moments of inertia, rotation about the intermediate axis is unstable. This was first discovered by cosmonaut Vladimir Dzhanibekov in 1985 during a mission to the Salyut 7 space station. He noticed that a wingnut--which had come spinning directly off of a bolt--maintained its initial orientation, then flipped 180 degrees. This is because the wingnut had three moments of inertia: through the hole, vertically across the hole, and horizontally across the hole. In this case, the tennis racket has three moments of inertia: one going from the butt of the handle to the tip of the racket, one going horizontally across the racket, and one going through the hole in the center of the racket. The one going through the hole is the intermediate axis, since the mass distribution from the hole is in between the largest (horizontally across the racket) and smallest (vertically across the racket) distributions. When the racket is spun about its intermediate axis, even a tiny disturbance can cause instability. The racket begins to rotate around the other, more stable axes in an attempt to conserve angular momentum. We can see this in the photo: the tennis racket does a full rotation along the axis going from the bottom of the handle to the top of the racket, even though I just flicked the racket towards me. 
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