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Re: The Olympics, egg drop



"centre of air resistance" is also called center of pressure (CP). When building
model rockets the CP must be after the center of mass for the rocket to fly
well. A rocket with CP at or before the CM will tumble - can be rather
exciting with a large engine. The rod used at launch is needed to allow the
rocket to reach a speed sufficient for CP to stabilize the rocket. Students are
most amazed when they find they need to add weight to the NOSE of the rocket to
make fly true. A string tied to the CM of rocket and then whirled in a horiz.
circle will usually show a bad case for CP position, but not a marginal one.
Maybe the egg drop projects could be spin tested like this prior to drop?

The Estes company has (had?) many wonderful books on the topic.

Date: Mon, 2 Oct 2000 07:19:00 +0200
From: Mark Sylvester
Subject: Re: The Olympics

John Barrer's egg drop project undoubtedly rotates because of air
resistance. A significant couple results from the fact that a structure
like the one he describes has the force of gravity acting at the centre of
mass, somewhere in the egg, significantly displaced from the "centre of air
resistance" on the whole structure. Sky divers exploit this effect by
arching their back and sticking out their limbs in order to fall belly-down.

Mark

John Barrer wrote:

Doug - I see your point, BUT if that's so, then "how
come" an egg drop project that is top-heavy will
rapidly tumble on its way to the floor. I have seen
many toothpick projects with the egg perched on top of
an elaborate energy-absorbing structure quickly rotate
in free fall so that the egg lands first! John Barrere



--

Scott

*****************************
S.Goelzer
Physics Teacher
Coe - Brown Northwood Academy
Northwood NH 03261
603-942-5531 ext43
sgoelzer@coebrownacademy.com
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