Lesson 1: Section 3: Physical Waves


Section 3: Physical Waves

There are two types of waves we will examine: traveling waves and standing waves.

Traveling Wave

Traveling waves in general are made up of some transmitted energy.  The energy is being transmitted from one place to another, and the wave can be seen to actually move in some direction.  Traveling waves have a crest (a high point) which can be visibly seen to move through a medium (such as a wave through water). 

When traveling waves meet, they temporarily combine and interfere with each other.  Unlike physical objects, waves can pass through each other unchanged except in the local region.  The following video shows a simulation of a traveling wave:

Traveling Wave Simulation

Traveling waves can have some or all of the energy reflect off of a boundary.  At a fixed point, all of the energy will reflect (like a voice reflecting off of a wall).  However, one can also see reflections when the wave travels between two "mediums".  A medium is that which is carrying the wave: air, water, even string can be a medium for a traveling waves.  The following video shows two different ropes tied together, one a heavy rope and one a light rope, with a wave excited down the length.

Traveling Wave Experiment

Standing Waves

Standing waves are made up of some transmitted energy interacting with some reflected energy.  A standing wave has a crest (a high point) which stays fixed in one place but vibrates up and down (such as a guitar string). It's common to find standing waves made up of two traveling waves (traveling in opposite directions).  The standing wave is the result of the constructive and destructive interference of the two waves.  The following video shows the difference between traveling waves and standing waves:

Standing Wave Simulation

Standing waves can be thought of as what happens with a jump rope or a guitar string.  The following video shows a standing wave generator which was made to show what the standing wave pattern looks like at different frequencies.

Standing Wave String Experiment