Don't give links or anything besides an answer to this problem When sound waves move through a medium, in what direction do the particles in the medium move?

The particles always move side to side.

The particles always move up and down.

The particles always move in the same direction as the wave.

The particles always move perpendicular to the direction of the wave.​

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?