A pendulum is constructed as a light thin`-` walled sphere of radius `R` filled up with water and suspended at the point `O` from a light rigid rod (figure). The distance between the point `O` and the centre of the sphere is equal to `l`. How many times will the small oscillations of such a pendulum change after the water freezes ? The visxosity of water and the change of its volume on freezes? The viscosity of water and the change of its volume on freezing are to be necglected.