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Dynamics cheat sheet

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15 Wheel spinning precession<br />

x<br />

MgL<br />

L<br />

y<br />

z<br />

Mg<br />

Wheel spinning around y-axis,<br />

hanging from ceiling<br />

Weight create a torque which<br />

changes the angular<br />

momentum<br />

Torque vector<br />

representation<br />

y<br />

<br />

Important: This<br />

analysis is valid<br />

only for LARGE<br />

y<br />

H Angular momentum<br />

x<br />

z<br />

y<br />

H y I yy y<br />

p<br />

y<br />

t<br />

Angular momentum<br />

change due to the<br />

torque applied<br />

After torque applied for t<br />

z<br />

This is what wheel will<br />

look like after del T<br />

time due to<br />

precesses, notice that<br />

SPIN angular<br />

momentum changes<br />

in the direction of the<br />

torque<br />

y<br />

Time it takes<br />

for the wheel<br />

to precesses<br />

one full cycle<br />

T p 2<br />

p<br />

H<br />

z<br />

Angular momentum<br />

after<br />

t<br />

t<br />

H aftert<br />

x<br />

H I yy y t<br />

x<br />

I yy y<br />

p<br />

y<br />

H t H<br />

t<br />

<br />

But<br />

H<br />

t<br />

I yy y p , hence I yy y p hence p <br />

<br />

I yy y<br />

MgL<br />

I yy y<br />

Nasser M.<br />

Abbasi<br />

Precesses.vsd<br />

6/1/2011<br />

Therefore, precession velocity p is MgL<br />

I yy y<br />

16 References<br />

1. Structural <strong>Dynamics</strong> 5th edition. Mario Paz, William Leigh<br />

63

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