This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!
Sound is a form of energy, and is caused by something vibrating. So what is moving to make sound energy?
Molecules. Molecules are vibrating back and forth at fairly high rates of speed, creating waves. Energy moves from place to place by waves. Sound energy moves by longitudinal waves (the waves that are like a slinky). The molecules vibrate back and forth, crashing into the molecules next to them, causing them to vibrate, and so on and so forth. All sounds come from vibrations.
Materials:
- 1 tongue-depressor size popsicle stick
- Three 3″ x 1/4″ rubber bands
- 2 index cards
- 3 feet of string (or yarn)
- scissors
- tape or hot glue
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What’s Going On?
Do you remember where all waves come from? Vibrating particles. Waves come from vibrating particles and are made up of vibrating particles.
Here’s rule one when it comes to waves…. the waves move, the particles don’t. The wave moves from place to place. The wave carries the energy from place to place. The particles however, stay put. Here’s a couple of examples to keep in mind.
If you’ve ever seen a crowd of people do the ‘wave’ in the stands of a sporting event you may have noticed that the people only vibrated up and down. They did not move along the wave. The wave, however, moved through the stands.
Another example would be a duck floating on a wavy lake. The duck is moving up and down (vibrating) just like the water particles but he is not moving with the waves. The waves move but the particles don’t. When I talk to you, the vibrating air molecules that made the sound in my mouth do not travel across the room into your ears. (Which is especially handy if I’ve just eaten an onion sandwich!) The energy from my mouth is moved, by waves, across the room.
Questions to Ask
- Does the shape of the index card matter?
- What happens if you change the number of rubber bands?
- What if you use a different thickness rubber band?
- What happens if you make the string longer or shorter?
- can you make a double by stacking two together?
- Can you get a second or third harmonic by swinging it around faster?
- Why do you need the index card at all?
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Sure thing! You attach the strong to one of the ends with the index card piece on it. Here’s the experiment video for you: https://www.sciencelearningspace.com/2009/07/harmonicas/ So happy you enjoyed the class!
My boys and I just saw the recording of the teleclass and could not see where the string was used in the harmonica experiment. Can you please explain? Otherwise we were thrilled to hear the experiment worked.Thanks
Yes, because it takes energy for the sound to travel through different mediums. 🙂
If sound is molecules vibrating and creating a domino effect with each other, then why doesn’t the sound travel on for ever and ever? Does the energy reduce?
Sound waves not only transmit through a medium, but also reflect back, depending on what the medium is made of and what the surface is like.
A noise barrier, or sound wall, is designed to reflect the noise in a different direction. They are usually made of materials that absorb sound differently than hard surfaces. Foam for example is a porous material which dampens the sound, because of all the gas pocket chambers inside the foam, and so it’s effective to dampen sound. This means that very little noise gets reflected back toward the source (or anywhere else). Streets are very reflective, so most of the noise from the highway is reflected back up to the source.
The main concept we’re having difficulty understanding is: If sound travels faster through solids than gases, why do we put up walls as sound barriers? I can hear my son much better without a wall/door between us, so it appears that sound travels faster through air.