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Kayaking Physics: Why it is easier to roll up when lying back rather than sitting up or forward

Delete this post Submitted by Jim Hubshman <jim@potomacpaddlers.com> on 19/Jul/2007

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"The moment of inertia of an object about a given axis describes how difficult it is to change its angular motion about that axis. For example, consider two discs (A and B) of the same mass. Disc A has a larger radius than disc B. Assuming that there is uniform thickness and mass distribution, it requires more effort to accelerate disc A (change its angular velocity) because its mass is distributed further from its axis of rotation. Quantitatively, disc A has a larger moment of inertia than disc B."

This quote from Wikipedia explains why it is easier to roll up when lying back rather than sitting up or forward. The closer you move your center of gravity to the axis of rotation (the boat) the less force/work required to roll the boat.

Wikipedia Link: http://en.wikipedia.org/wiki/Moment_of_inertia

Jim


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