It means that the sphere where it meets the surface it's rolling on, does not slide -- the instantaneous point of contact is stationary with respect to the "ground" surface.ok i got the answer. thank you.
i have a question though, i wanna know what the question means when it says that the sphere rolls without slipping??
okay, then what would it be?When an object rolls without slipping, it means the velocity of the center of mass is equal to the radius times angular velocity, [itex]v_{cm}=r\omega[/itex]
This is called the nonslip condition. When an object rolls with slipping, the linear velocity is not [itex]r\omega[/itex]