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.
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).