introduction to oscilliations

This is an interesting subject indeed. When energy passes through a medium in the form of waves it is an harmonic motion. We can see formation of waves but not in air or through solids.If we assume energy flows through any medium in the same fashion then the matter through which energy flows rises or falls in a sinesoidal curve.

If an object falls from a height, how does it apportion its energy between sound energy and physical energy causing vibrations? If energy is some sort of a force,then F=mxa, then what is mass?

If electricity is an energy, instead of charge phisically moving forward, dose it move up and down like in a wave form.

In the case of a bridge structure, how does one arrive at its natural frequency? What vibrations cause resonance? Because of movement of vehicles plying over it or vibrations due to wind force?