Drinking glass

A drinking glass has a round base with radius r1, height of h and radius r2 > r1 at the upper rim. On its side on the table the glass goes around in a circle. How many full rotations does the glass do during one such circle?

I get {[h^2 + (r2-r1)^2]^(1/2)}/(r2-r1).

Originally posted by talzamir
A drinking glass has a round base with radius r1, height of h and radius r2 > r1 at the upper rim. On its side on the table the glass goes around in a circle. How many full rotations does the glass do during one such circle?

I'll say

Theta = 2*pi*(r2-r1)/h

Theta = 2*pi

so number of rotations is

N = (r2-r1)/h

Originally posted by joe shmo
I'll say

Theta = 2*pi*(r2-r1)/h

Theta = 2*pi

so number of rotations is

N = (r2-r1)/h

I do not think your answer will yield the right trends with respect to parameter variations. For example, consider if (r2-r1) becomes very small (for some constant h). N should get very big because the glass will sweep out a very large circle, right?

Originally posted by LemonJello
I do not think your answer will yield the right trends with respect to parameter variations. For example, consider if (r2-r1) becomes very small (for some constant h). N should get very big because the glass will sweep out a very large circle, right?

yeah...I suppose so. I did it hastily while I'm slightly under the influence...sorry