# Waves and sound

Surfing, talking on cell phone, listening to music, playing guitar…

Is there a physical phenomenon common to all these actions?

You have probably often heard the word "wave" or words derived from it. The waves are present in the light that illuminates the day; in the operation of the cell phone, the TV, the radio, the microwave, the chatting of your friends, the music you listen to… they are present almost everywhere.

## What is a wave?

Consider a taut rope with one end attached to a wall and the other held by a person. If the person performs a rhythmic up-and-down motion with the hand, it will cause a wave to propagate on the taut rope, as shown in the drawing.

Although the wave moves from left to right, the rope does not move in that direction. The various sections of the rope perform only up and down movement, but the rope continues with a wave attached to the person's hand and the other end attached to the wall. In other words, when a wave propagates on a rope it does not take the rope with it.

## The wave concept

Waves are regular disturbances that propagate but do not carry matter. Waves only carry energy. Wave is the part of physics that studies waves and their related phenomena.

## Wave Types

The waves that we produce by playing the strings of a guitar or those that propagate in a lake where we throw a rock are called mechanical waves.

Mechanical waves they are those that need a material medium to propagate. The waves of the sea and the waves we produce on a guitar string, the sound, are examples of mechanical waves.

However, not all waves need a medium for their propagation. Light, for example, is a sun-emitted wave that travels to Earth without a material medium between them. This also occurs with radio waves, x-ray waves and thermal waves. These waves called electromagnetic wavesthey propagate in both matter and vacuum, that is, in a place without any matter.

The waves fall into mechanical waves - those that need a material medium to propagate - and electromagnetic waves - they do not need a material medium to propagate.