Mini- Lesson: A Big Splash!

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Students learn about waves created through displacement.

Big Idea

Students drop several different sized objects into a bucket of water and observe what happens by measuring how long the wave continues after the displacement.

Engaging the Group

10 minutes

I opened up this mini lesson today with simply writing the word "displacement" on the white board in the lab. In order for the wave standards to be satisfied and to deepen their understanding of how energy is transferred in waves, I wanted them to explore this type of energy by giving them three different variables, and a way to easily measure the differences. As I pronounced the word, I asked them if they had ever heard it? Nope. Not one student did. 

"What does the word sound like?" I asked. Several answers came around, but one student said "misplaced." I used that word to build on understanding, but didn't give away the meaning. I told them that it is sort of like being misplaced or pushed out of the way, but there was energy involved. 

I told them that I was going to demonstrate what needed to be done and I wanted them to watch. I used a smaller container at first in the center of the table so that the displacement would be very visible to all of my students at one time. Dropping the marble from the top of a meter stick would make them understand that the height had to be the constant. As I demonstrated what needed to be done, I showed them the three items they would drop: a cork, a large shooter marble and a larger rock. ( The rock didn't disappoint us and got everything and everyone very wet!) As soon as the rock dropped, we watched the container's wave motion until it stopped. I told them that they would time it from the moment the object hit the water and that one person would film it until it stopped moving. Instead of focusing on timing during my demonstration, I asked them to tell me when they thought the water stopped moving, so we could clearly define what that looked like. 

I explained that it was alright that the water toppled over the edge, but that they should be careful to wipe up any spills so no one slipped. As I closed the first section, I pointed back at the word displacement. I told them to think carefully about the word and try to figure out where it fits into the experience of energy, making the waves and creating energy. 


Trying It Out!

20 minutes

Materials for the Investigation: Meter stick, iPad for video, iPad for timer, ice cream pails filled with water dyed green or blue, paper towels for spills, a cork, a large shooter marble & a large rock that is larger than the marble. 

I passed out the Transfer of Energy Displacement data sheet. We read each step out loud together as I reviewed what needed to be done. instead of using the shallower containers, I had filled up ice cream buckets around the room and filled with water. I put green dye in each of the buckets so that the waves in the water would be more visible. They had more area to spread out in an ice cream bucket.

I asked a team of four to volunteer for the demonstration as I showed them once more how the team should work. One person placed the meter stick in the water, as it marks the height in which the objects will be dropped.  The object is dropped from one meter and it is the constant. This measurement task supports their understanding of measuring to one meter, the appropriate tool for doing so and helps them focus on understanding that this creates on aspect of the investigation that is continually the same. The timing would be the other measurement task as they watch the waves and the time is measured. This data is then recorded and will be the data they will compare as they draw conclusions about which created the most energy.

To prod and support their understanding, I asked why they thought it might be important to keep the height the same? One student said that if we dropped the rock from standing on a chair, it would splash a lot more and it wouldn't be the same. I explained that the objects needed the same height so that the chances of the displacement would be the same. I asked the group what their prediction was about the objects since I simply demonstrated with a marble earlier. They predicted different things and so I encouraged them to discuss the possibilities in their groups and not think As they dropped the cork, we talked about timing it until it stopped. I coached them to wait until there was no more motion in the water before they turned off the timer. Then, they continued by dropping the marble. Finally they dropped the rock and could see how much more time it took to have the waves stop. Each group took their turns and tried out each object. There was a lot of chatter, some had to start over because the timer was turned off too soon. But, the simple experiment really showed them how energy is in the displacemet from the object to the water and how waves carried that energy. As worked, they also filmed the process, catching the displacemet on film in frames of the waves to study and observe when they were done and proving their evidence. 

Reflecting Upon Our Understanding

15 minutes

As I roved around as students worked on understanding displacement more, I encouraged them to discuss it among themselves in their small groups. We talked about what needed to be proven on the  displacement paper and that evidence is key in presenting our findings. Why was there a transfer of energy? What evidence is there? Can you prove what you saw?

They looked at their movies of the process and discussed how transfer of energy was happening and where it was happening. They finished their papers to reflect on what they proved; that energy was transferred  in waves created by displacement.

Our closure was to share a few of our observations. I emphasized how important it was to use their evidence to talk about the difference in the energy the different objects created. They all shared that the rock obviously created the most displacement because of the amount of water on the floor. They could understand that the larger the wave, the more energy had been transferred.

This lesson was a really fun and simple way to really drive home the idea of energy transfer.