Can Some1 help?? When using the "ball and stick" drawing method of drawing a compound, which element usually goes in the center of the model?

1. do the particles in the medium material move in the same direction of the wave or at opposite direction to the wave? explain your answer. 2. by inputting more energy into the wave, i.e a large shake of the spring, which wave property also increases? 3. are there forces of friction acting while a wave is passing through a medium?