Transverse and Longitudinal Waves
Physical Science
Name: ___________________________________________ Period: ________ Date: _________
Essential Question: How is transverse wave different from longitudinal wave?
Two kinds of waves: transverse and longitudinal
Suppose a piece of wood is floating on the surface of a pond. You throw a rock into the pond and create
a ripple of waves. The waves move outwards from where the rock hit. When the waves pass the wood, it
bobs up and down. The wood does not move in the same direction as the wave is moving, but rather it
moves in a direction perpendicular (vertical; straight up and down; upright) to the travel of the wave,
i.e. transverse.
In the case of the falling dominoes, the movement of the dominoes was in the direction parallel to the
movement of the wave, i.e. longitudinal. Another example of a longitudinal wave is a P wave or primary
wave during an earthquake. P waves are also known as compressional waves, because of the pushing
and pulling they do.
Sound waves are longitudinal. When we speak, the vocal cords vibrate the air, setting it into motion. The
molecules of air vibrate in the same direction as the vibration of your vocal cords. These molecules in
turn vibrate the molecules next to them, and so on. The region in which the molecules get pushed
becomes more dense then the region around it, because more molecules are there. The increased
density pushes these neighboring molecules further ahead and the sound travels. This sort of
longitudinal wave is also called a pressure or compression wave.
Earthquakes can also be compression waves. One of the things that I study is to compress crystals and
see how the atoms respond. The ease in which a material can be compressed is related to the speed in
which sound waves can travel through it. For instance, diamond is very incompressible, and sound
waves, or compression waves, travel through it very fast.
The speed of sound in air varies depending upon the temperature or density of the air. Hot air has lower
density and therefore sound travels slower. Sound travels faster through cold air.
Amplitude is not tied into the equation relating the other 3 wave parameters. It can be anything it wants
to be. The amplitude of a sound wave is how loud the sound is. The unit of measurement for the
amplitude of a sound wave is called decibels. For an earthquake, the Richter scale measures the
amplitude. The greater the amplitude the greater the displacement of the earth, and the greater the
damage. http://www.geo.arizona.edu/xtal/nats101/s04-12.html
Clarifying Questions:
1. What are the two types of waves?
_____________________________________________________________________________________
_____________________________________________________________________________________
2. What happens when you throw a rock on a pond?
_____________________________________________________________________________________
_____________________________________________________________________________________
3. What does it mean by perpendicular?
_____________________________________________________________________________________
_____________________________________________________________________________________
4. What is a transverse wave?
_____________________________________________________________________________________
_____________________________________________________________________________________
5. Why are falling dominoes an example of longitudinal wave?
____________________________________________________________
____________________________________________________________________________________
6. Draw and label a transverse wave
6. Draw and label a longitudinal wave
7. Why is sound wave considered as a longitudinal wave? Think!
_____________________________________________________________________________________
_____________________________________________________________________________________
8. Why is earthquake as example of longitudinal-compressional wave? Think!
_____________________________________________________________________________________
_____________________________________________________________________________________
9. What determines the speed of sound in air?
_____________________________________________________________________________________
10. Why do sound travel faster in cold air? Explain. Think!
_____________________________________________________________________________________
_____________________________________________________________________________________
11. What is amplitude? What is its unit?
_____________________________________________________________________________________
_____________________________________________________________________________________
12. What is the relationship between amplitude and the displacement of the earth?
_____________________________________________________________________________________
_____________________________________________________________________________________