What is the relation between the velocity, frequency and wavelength of a wave called? What is the wave called in which the particles of the medium move back and forth along the direction of propagation of wave? Who invented the first pendulum clock? Which of the following is the type of mechanical waves? What is the change of path of water waves while passing from a region of deep water to that of shallower one called? If the mass is at rest in mean position, how much will be the resultant force on the mass?