As you’re relaxing on the beach, listening to the rhythm of the tide, we interrupt your reverie to say, “Hey, this would make a great science lesson!”
Yes, we’re nerdy that way. Sorry.
The pulse of the ocean waves as they crash into the shore is a wonderful, hypnotic sound. But it is also a great reminder of how fascinating science is, and how vitally important waves — not just ocean waves — are to life on earth.
Waves of light, sound and motion are all around us, and they each move very differently. Fascinatingly enough, if science didn’t get those types of waves exactly right for their exact purposes, we might never hear those ocean waves.
There are three main types of waves, as characterized by how they move particles:
Longitudinal: The movement, or disturbance, of the particles is parallel to the wave’s movement. Sound waves through air are longitudinal.
Transverse: The movement of the particles is perpendicular to the wave’s motion. Light waves are an example of transverse waves.
Surface: The particles move in a circular motion — like those ocean waves.
Try this interactive wave-maker from Science Primer to see the differences:
Of those three waves types, only one — longitudinal — activates our eardrums, allowing us to hear sound waves as they travel through the air. They compress particles as they travel, and that compression hits our eardrum. Our brain then can identify that sound based on the unique frequency of the wave.
Our own Discovery Dan shares a fun way you and your students can demonstrate this.
You can also use a Slinky to do a hands-on demonstration of the difference between transverse and longitudinal waves.
1. Stretch the Slinky between two students on the ground. Do not allow them to over-stretch it.
2. To create a longitudinal wave, have Student A hold their end completely still. Have Student B push their end of the Slinky back and forth toward their partner. They will notice how the springs bounce off each other, sending the “wave” down the Slinky to their partner.
This can also be demonstrated if Student A releases their end, and Student B continues the pulsing movement.
3. To create a transverse wave, have Student A again hold their end completely still. Have Student B sweep their end back and forth, left and right. The wave motion will make the rest of the Slinky follow suit, all the way down to their partner. The motion in this wave is moving back and forth similar to Student B’s arm motion.
If you don’t have any Slinky’s handy, the University of Colorado-Boulder has a free lesson plan that uses your students to demonstrate the motion of these two waves. Of course, as you already know way too well, you might want to be careful of the whole “pushing each other” part, as suggested in the lesson. We all know how that usually ends up. It might be better to have the students push against each other’s hands.
PBS Learning also has some fun ideas, videos and activities for teaching sound waves as well.
If you want to surf some more into sound-wave science, check out these sites:
Alright, we’ll let you go back to your sand, sun and relaxation. Enjoy!