Hii could someone answer these for me please. thank you so much for your time.

How is sound energy produced a. vibrating objects b. objects being heated c. temperature differences d. stationary objects

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.

Are formed where bumps from two surfaces come into contact ?