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robb_
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Homework Statement
A sphere of radius rho is constrained to roll without slipping on the lower half of a hollow cylinder of radius R. Determine the Lagrangian function, the equation of constraint, and equations of motion.
Homework Equations
U = mgh
Lagrange's eqns of motion
T= .5 mv^2 + .5 I w^2
The Attempt at a Solution
Let me work this in cylindrical coords. Let theta be the angle between where the sphere is at the bottom of the cylinder and where it might lie some distance up the side of the cylinder. With this, the height can be written as R cos(theta). This gives me the potential energy term in the L eqns. The kinetic energy is a sum of translational and rotational. The translational term looks like .5 m (r^2*theta_dot ^2 + z_dot^2). There is no r_dot term since it is constrained to lie on the surface. The rotational kinetic energy term should look like .5 (2/5 m rho^2)*w^2. (Sorry that I am using w for omega.) So is this okay so far? I am having trouble with the eqn of constraint. I can see that the arclength traversed by the sphere is equal to the arclength traced out on the cylinder. This seems to introduce another coordinate though- the angle rotated out on the sphere itself. Does that make sence? thanks