We completed the “Dunkin’ for Density” activity today, collected our data, entered it into excel, and discussed our findings.
For this lesson, the kids had to make 1 film canister float, 1 film canister suspend, and 1 film canister sink in water by changing their densities. We used white/clear plastic film canisters and I calculated the volume as 39 ml or cm3 by using water displacement and a large graduated cylinder. (The film canisters hold about 35 mL of water, in case you were wondering!)
Supplies: plastic tray, 3 film canisters per set of two lab partners, a bowl or large beaker filled with water, pennies, rubber stoppers, cork stoppers, paper clips, and bits of clay. I also had a really large/deep bowl as the “official suspend testing tank”. Once the kids tested their suspending canister, they brought it over to be officially checked by me.
Using whatever combination they like, they place the items into the film canisters to complete the task. I only have two rules: you must have at least one item in the canister (which I forgot to tell the 1st class!) and it must be able to close and seal tightly so no water enters the film canister. The floaters and sinkers are the easiest to do and the kids figure those out pretty quickly. But I am very picky about my definition of suspend and it drives them nutty! In order to qualify as a suspender, the film canister has to touch the bottom of the bowl when I tap it, and then float up slowly until it is near the surface of the water. Only a small part, if any, may rise above the water line. This is a great problem solving activity and after a few tries, they usually get just the right combination of stuff inside their film canisters to make the density very close to 1 g/cm3. (For this to happen, the mass ends up being close to 39 g,)
Once they have completed all three tasks, they use the TBB to find and record the mass into their notebooks. (Tip – make sure the film canisters are dry before they use the TBB) (Tip #2 – have them find the mass of an empty film cansiter before they begin dunking.) Using the formula for density (D=m/v), they find and record those densities into their notebooks. Once everyone is done, each group reports their data and we enter it into the excel spreadsheet, displaying the data on the SmartBoard. We then discuss the data and I ask the kids if they notice any patterns in the data. (Sometimes I’ll show the data from previous classes so they can compare their results to older experiments.)
After we have discussed the data, they answer the analysis questions and write a conclusion on page 41, the right side of their notebook. The one misconception that some kids may have is that the film canisters sank because they became heavier. We talk about how yes, they did get heavier, but they sank because they became denser.
If you have completed this activity, I would love to hear from you and see your results!