## Super Easy to Make Cartesian Divers

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?!

Materials

• 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
• paper towels
• 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:

1. Be careful bending the straw, any cracks will make the the straw useless.
2. 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)
3. 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)
4. Use a rescue hook for any divers that do not float back to the top.
5. Remind students to place the cap back on the bottle TIGHTLY – or water will shoot out of the bottle when they squeeze it.
6. Lunch or serving trays work nicely to contain spills.