Grade 5 Physics: Waves

We are doing a three-week study on physics, as mentioned in the previous physics blog. I plan on spending a couple of days on each concept. The plan is below. There is a previous post on our introduction to energy, force, and momentum and simple machines. 

Introduce Energy, Force, and Momentum2 days
Simple Machines3 days
Waves and Sound2 days
Light2 days
Magnets2 days
Electricity2 days

If you need a refresher on Physics or are learning it for the first time (like I did a few years ago) these resources came in useful to me.

Physics for Kids (middle school level)

The Physics Classroom (high school level)

The second concept that we are exploring in our Grade 5 Physics Block is waves. I think this might be one of the more exciting concepts, because the demonstrations and experiments are so tactile. To demonstrate transverse waves, we made a wave machine from duct tape, bamboo skewers and gummy snacks. For the longitudinal wave we used a slinky and a couple of homemade Chladni plates. Below are instructions for each and some basics on how I presented them, which was mostly a ‘notice and wonder’ exercise where we made observations and then guessed the meaning of that observation.

Physics for Kids had very little on waves, but the Physics’ Classroom has quite a bit. You can also find several diagrams on the web in regards to the anatomy of a wave. 

We discovered the following terms in these exercises or discussed them after the exercises:

amplitudewave lengthcrest
troughequilibriumtransverse waves
longitudinal wavescompressionsexpansions
standing wavenodesantinodes

Day 1 – Introduction to Waves

Wave Machine

The wave machine is a project that we have done a couple of times. It is simple to make and perfect at demonstrating a wave and how they work. To construct the wave, we used:

Duct tape
Gummy snacks 
Bamboo Skewers

We first stretched a piece of duct tape between two chairs so that it was taunt. We then placed a gummy on each end of the bamboo skewers until we used all of our gummies. The more gummies used, the longer the wave machine. Concepts are easier to see with a longer machine, but you are also balancing the tautness of the duct tape. We used two bags of gummies. You might consider 3 bags, but between 2 and 3 would probably work best. The gummies need to be roughly the same distance from the edge of the skewer. From here we placed the skewers at equal intervals (approximately 3 to 4 inches apart) along the duct tape, in the middle of the skewer. Adjustments are made as we go along to keep the wave machine horizonal and not tilting to any one side. Below is a video from where we constructed a previous wave machine.

When the wave machine was made, we begin to play. “Let’s see how small a wave we can make!” and “How big do you think we can make it?” After a few minutes of this, I began to ask leading questions. Some of these questions were adapted from Building Foundations in Scientific Understanding, Volume I. The exercise was C-10, Part 2 on waves. 

  • What is moving? Obviously, the gummies are not moving along the wave. (Energy)
  • Where else do we see waves? (The most obvious is water. We know that we also experience them in the air as sound waves.)
  • What makes the wave big or little? (Amplitude is the technical term, but it is the wave height that we were noticing in our play.)
  • What about the speed? Does that change? (The speed of the wave (frequency, which changes with wave length, does not really change without changing the machine.)
  • What could we change about the machine and how would it change the wave? (You can move the gummy’s closer to the center. This changes the wavelength of the wave, thus changing its frequency. The longer the wave machine the easier to see this.)
  • We talk about how this wave is called a transverse wave. I do not go into detail with her, but a transverse wave runs perpendicular to the medium it travels through. 
  • We also talked about a standing wave, which was important to know leading into the work with the Chladni plates. We attempted, successfully I’m happy to report, to make a standing wave by pulsing the wave machine.

The Slinky

To demonstrate a longitudinal wave, such as a sound wave, we used the slinky. To do this, we simply each held an end of the slinky and pulled it slightly apart so we could see each of the links. Then one of us would gently push it forward and pull it back quickly. We then watched the compressions move along the slinky. We video recorded this, and played back in slow motion to see the compressions more easily.

We played for a few minutes with the slinky, and then we discussed how this wave was different.

  • How was this wave different from the other? (Instead of moving up and down, these links become closer together and then farther apart.)
  • What would the amplitude be on this wave? (It is still from the equilibrium to the top of the coils)
  • What would the wave length be? (From compression to compression)
  • We discussed how sound waves were longitudinal waves.
  • We did not attempt it, but you could attempt to make a standing wave. 

Day 2 – Chladni Plates

This also is an exercise that we have done before. Below is a short tutorial to make personal plates with a yogurt cup, a dark-colored balloon, salt and a paper-towel tube. After constructed, have the child make sounds into the tube and see the vibration of salt on the balloon. If the child immolates single tones, they should be able to see various patterns on their balloon. 

To construct a larger plate, we used a large bowl, a Bluetooth speaker, a tablet or phone connected to the speaker, and an extra-large balloon

  • We connected the speaker to the device via Bluetooth first. 
  • We then placed the speaker, speaker-side up, into the bowl. 
  • After cutting the neck off of the balloon, we stretched the balloon taunt over the bowl. 
  • We sprinkled chili powder, in place of salt for the contrast against the light-colored balloon, on the entire surface of the balloon.
  • From here we used this tone generator by Tony Szynalsky and played different tones to see different patterns.

After we had played several minutes with all the tones and even some music, we went back to the tones and started looking for patterns discussing what we noticed:

  • The designs have smaller circles with higher frequencies.
  • The designs have bigger circles with lower frequencies. 
  • We discussed standing waves again, and what the areas that were not moving were called (nodes) and the moving parts (antinodes.)
  • We also discussed why the pattern between the frequencies and the size of the circle might be true. We decided that was likely because of the wave length.

And that concluded our exploration of waves. It was a rather messy one, but a very successful one.

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