Cartesian Diver -Lab Follow Up Questions
Directions: Discuss with your partner and then write complete sentences to answer the following questions.
1) Where does the force that changes the conditions in the bottle come from?
2) Describe the changes inside the diver during the application of force.
3) Can you change the mass of the diver without opening up the bottle and adding or subtracting matter? Explain.
4) Can you change the volume of air inside the pipette without opening up the bottle? Explain?
5) What two kinds of measurements are required to figure out the density of an object?
6) Describe how a buoyant diver can become a sunken diver and use the following words appropriately. **pressure, air, mass, volume, more dense, less dense, buoyant**
7) To be neutrally buoyant, an object must not rise to the surface or sink to the bottom. How can you keep your diver neutrally buoyant?
8) What living creature acts much like a Cartesian diver? What is similar and what is different about the way this creature maintains its neutral buoyancy?
Cartesian Diver
Objective: Density and pressure effects are explored using a simple visual demonstration.
Ingredients
• large plastic bottle (~2L) with lid, filled with water
• glass filled with water (for testing the ‘diver’)
• pipette
• materials that sink
• In class we will keep it simple… but at home…craft supplies and creative ideas for attaching materials to the pipette (string, safety pins, waterproof glue, etc)
*You may choose to use another object other than a pipette for your diver. Soy
Sauce packets, straws, eye droppers, and other air trapping objects work also.
Instructions.
1. Choose a space that can get wet and is easy to clean up. 2. Add weight to the pipette.
3. Check that the pipette just floats in the glass of water.
Itshould slowlyrise to the top of the water after you drop it in. If it sinks, remove some of
the weight. If it floats too easily add some more weight. 4. Drop the pipette'diver' into the
bottle. 5. Re-Fill the bottle with water from the glass if necessary. You want the water all the way to the top. 6. Screw the cap on thebottle. 7. Squeeze the sides of the bottle (firmly). The diver will sink throughthewater. Let go of the bottle and the diver will float back up to the top.
How does it work?
The diver contains an air bubble trapped inside. The combined density of thepipette (and all attached to it) is slightly lower than that of the water, so it floats. When yousqueeze the sides of the bottle you increase the pressure pushing on the air bubble,making it compress into a smaller space. This decrease in volume causes the airbubble to increase in density. Therefore the overall density of the diver will nowbe greater than that of the surrounding water, making it sink. Releasing the pressure(by stopping squeezing the bottle) allows the air bubble to expand back to its normalsize, and so the diver will float again.
Tips for Success
Don't be scared about pushing hard on the sides of the bottle – they can take a lot of force. It may be easier to rest the bottle on a flat surface and then use both hands topush the sides.If your diver keeps floating then try squeezing out some bubbles of air. Or, take it out and add more weight, making sure to testit in the glass of water to be sure that it doesn't immediately sink – you'll find it easier toget it out of the glass than out of the bottle if it does sink! Fill the bottle all the way to the top before putting the cap on.
Did You Know?
Sperm whales regularly dive to depths of at least 1000m where the water pressure is on the order of 100 atmospheres. In the process, the rib cage will fold and collapseand the lungs will compress down to one per cent of their size at the surface. Theassociated change in buoyancy is essential to keep the animal at such a greatdepth. They also regulate their own density when they sleep a short distance below the surface, facing head first towards the bottom of the ocean. While drifting along with the current, going neither up nor down, they sleep by keeping neutral buoyancy. These whales have a special ability to use muscles to squeeze and compress air inside their bodies, much like when you apply force and pressure to your Cartesian Diver.