Set up hints – students prep items at their table then come up to the tank. After dunking, dry off with towels (I just drop it onto a thick folded up towel next to the tank). I have a bank of TBBs set up on the side of the classroom – students find the mass on their assigned TBBs then record results. Repeat trials. Towards the end of class, students enter all their data into the spreadsheet then I give them the volume of their film canister. Depending on the type of film canister, the volumes are about 39-41 mL. Confirm with a large graduated cylinder or water displacement tank.
This sugar density activity is one I have never tried before, I actually ‘borrowed’ the idea from my son’s HS Chemistry Teacher. He came home and told me they made different colored layers using only sugar, food coloring, and water. I immediately jumped on the computer and thought about how to use this in my 6th grade classes, we are in the middle of our density unit and it would be a perfect opportunity to try it out.
One of my goals for this year is re-examine my lessons and see which activities I can make more open-ended when appropriate. For this activity, most of the resources I found told the students exactly how much sugar to put in each layer and what order to place the colors into the test tube or some other type of container. I didn’t want my students to follow step by step procedures, but wanted it to be more of an exploration type of activity. I had no idea how this would turn out but gave it shot anyway.
I gave them the problem, the parameters, the tools to complete the activity, and sent them on their way. It was great to see them figure out how to solve the problem, talk out strategies, and to see them go through the trial and error process. Each group came up with a different way to solve the problem and some groups struggled more than others. I met with each group to facilitate, ask questions, and had them explain to me what they were doing and why. Overall, it was a successful lesson, they enjoyed the activity, and it really solidified their understanding of density.
I am also incorporating more open ended writing in science and I enjoyed reading their reflections about the activity.
This was the easiest, and most inexpensive way to make cartesian divers I have ever tried, and each student got to take theirs home after class. Did I mention how much fun it was?!
semi-transparent to transparent bendy straws – 1 per student
colored paper clips – 4-6 per student
scissors – 1 per 2-4 students
2L bottle with cap – 1 per 2 students
beaker of water – 1 per 2-4 students
tray to contain spills -1 per 2 students
optional: eye dropper with blue colored water
Part 1 – Demonstration:
As part of our density unit, we talk about the concept of buoyancy – why do objects float or sink? Using a 2L bottle of water, a glass medicine dropper, and some blue food coloring, we made guesses and observations about the cartesian diver.
The medicine dropper is filled with blue water, checked for buoyancy, and then added to a 2L bottle. Students gather to make observations. What do you think will happen when I squeeze the bottle? What will the blue water do? Why did it sink? Why did it float? What is happening to the air in the diver? What is the water doing? Did the mass of the diver change? The density? Students share their ideas and we come to a conclusion as to why the diver floats and sinks.
Part 2 – Build and Explore:
After the demonstrations, students get to build their own divers and explore on their own. Some tips to keep in mind:
Be careful bending the straw, any cracks will make the the straw useless.
After bending the straw, cut off the excess length of straw so that both side are equal in length. (You can save the rest of the straw for future activities)
Attach one paper clip as shown in the diagram below. Additional paper clips can be easily added or removed by sliding them on or off the main paper clip. (Like keys on a keychain)
Use a rescue hook for any divers that do not float back to the top.
Remind students to place the cap back on the bottle TIGHTLY – or water will shoot out of the bottle when they squeeze it.
Lunch or serving trays work nicely to contain spills.
For this activity, I used the set of density blocks from Flinn Scientific. Each group of students had 6 blocks made of the same material. Their challenge was to identify the material using their measurement skills to calculate the mass, volume, and density of each block. This activity also reinforced the concept that the density of an object is constant.
Demo & Discussion – For this part of the lesson, students will not handle the bottles, they will answer discussion questions based on their observations only.
Share observations about the bottles.
What do the bottles have in common?
What is different about the bottles?
What do you think the original contents of the bottle were?
What phases of matter are shown?
Are any of these bottles empty? Explain.
Do all of these bottles have air in them?
Which bottle has more air in it: Cotton Balls or Water? Explain.
Which bottle is filled the most? Least?
Which bottle has has the most ‘stuff’ in it? Least?
Which bottle is the heaviest? Lightest?
How would you order these bottles from lightest to heaviest?
Estimate the mass of each bottle in grams.
Which bottle is the densest?
How would you arrange these bottles from least to most dense?
Which of these bottles can have more of the same ‘stuff’ added to the inside of the bottle? Explain.
Which bottle(s) would float in a tank of water? (I do this at the very end of the lesson with everyone at the sink)
Hands On Exploration
Each group will have one set of bottles or take turns using the demo bottles and sharing their findings.
Using a triple beam balance, the volume of the bottles, and a tank of water, answer as many of the questions above as you can. (for our calculations, we use the volume of the bottle’s original content (500 mL of sport drink) to give us an approximate density, not the actual density – for comparison purposes only)
How did your findings compare to your observations and predictions?
Dunk tank – time to find out which one will float!
Give each group of students a new set of bottles (ones that they have brought in from home) and have them make observations, predictions, and density calculations.
Additional Bottle Ideas:
laundry detergent – liquid or powder
different shapes of pasta
pop corn kernels or popped
Have each student bring in a bottle from home filled with the contents of their choice so that you have enough bottle to compare. Match similar bottle shapes/sizes together for each group or match similar contents in different sized bottles for comparison.
You can also use these bottles as part of a Triple Beam Balance Activity (blog entry).
This is a wonderful problem solving and hands-on activity to use as part of your density unit. The students enjoy the challenge and have a solid understanding of density after completing this activity. Even though students quickly figure out how to make the canister float and sink, making the canister suspend is pretty challenging and requires a lot of trial and error and problem solving.
To qualify as suspending, the film canister needs to float just under the surface of the water, with a small portion of the top just breaking through. How I also verify that it is suspending is by pushing the film canister to the bottom of the tank, if it comes up very slowly to the surface, it counts – if it comes up quickly or stays towards the bottom, it doesn’t count. Students then need to figure out that if it comes up too quickly, they need to add to the mass, if it comes up too slowly, they need to remove some of the mass. It will take several tries to get it just right.
one canister per 2 people works well, they can reuse the canisters if you don’t have enough to give each set of lab partners 3 canisters
if they reuse the canisters, be sure that they find the mass before they empty the contents
An assortment of small objects such as pennies, paper clips, stoppers, small pebbles, etc…
Introduce the Dunkin’ for Density Challenge – their goal is to make the film canister float, suspend, and sink by placing contents inside of the film canister.
Many students will say that the canister will float with nothing in it, but they must place a few objects in it for it to count 😉
On a side note, a mini history lesson on film and cameras is fun to discuss since most students have never used a camera that used film
Explain the procedures, review how to use the TBB, note that the film canister must seal completely and be air tight so that water doesn’t enter, and also demonstrate how to use the dunk tank properly and to dry off the canister before finding the mass.
Do not give the students the value for the volume of the film canisters until they have collected their data. If the students know the volume of the film canister, they may figure out the mass needed to make the film canister’s density close to 1.0 g/cm3.
The value is approximately 39 mL or 39 g/cm3 – verify with a large graduated cylinder that the film canister can fit inside of – or use an overflow can to find the volume (link).
I will give the volume to each set of lab partners individually and ask that they don’t share that information with the class.
Once students have calculated the density, collect class data on a spreadsheet projected on the board/screen.
Discuss results – why did the film canister float, suspend, or sink in the tank of water? What relationships did you notice?
For more lessons related to the Properties of Matter, click here (link)
Above is a photo of a 4-door foldable for the three density related formulas: D= M/V, V= M/D, and M = VxD. The 4th door has step by step instructions on how to solve a word problem. Along with the formulas, inside the foldable are 3 practice problems, and a few notes about mass, volume, and density.
On the right side of the notebook are practice problems. Students have to determine which formula is needed, set up the problem, solve, and add the correct units. They can refer to their foldable for the formula and how to solve the problems. I have the students close the flaps for the known values. For example, if the problem states the Density and Volume values, they close those doors on the foldable leaving the Mass flap open, since it is the missing value. That is formula they will then use to set up the problem correctly and solve.
My main goal for this lesson is having the students choose the right formula, set up the formula by plugging in the known values (this is a step that the kids don’t feel the need to do/show as part of their work), and adding the correct units when done. Some students may have a little difficulty with multiplying or dividing decimals and rounding to the 100ths place, so I usually go over that before we begin by modeling a few problems with them.