How many revolutions per minute would a 20 m -diameter ferris wheel need to make for the passengers to feel "weightless" at the topmost point?

The general equation for the forces acting on the passengers at the topmost point of the ferris wheel is

where
mg is the weight of the passengers
R is the normal reaction of the cabin
is the centripetal force

In order to feel weightless, the normal reaction felt by the passengers should be zero. Therefore, the equation becomes:

or

where  is the angular frequency of the wheel and r is its radius. Since we know its radius, 

we can calculate the angular frequency:

From which we find the frequency at which the ferris wheel should rotate:

This is the number of revolutions per second, so the number of revolutions per minute will be

The rocks expand when there hot/warm  and contract when they are cold.