Cartesian Driver

Materials

• 1 piece of metal Wire
• Plastic Vial
• Plastic Bottle with a Lid
• Water (not included)

Extended Science Materials

• Condiment packet such from your favorite restaurant.
• Plastic water bottle.

Procedure

1. Key terms to research: buoyancy, mass, pressure and volume.
2. After research of key terms, take your vial and break off its lid (if you have scissors, you can cut it). Grab your piece of metal wire and wrap it over top the opening of the vile.
3. Add water up to the neck of your plastic bottle and place the diver into the water. Add or remove water until it floats, with the tip barely sticking out of the water.
4. Screw the bottle cap on tightly, then squeeze the sides of the bottle. What happens to the diver? Why do you believe this happens?
5. STOP squeezing the bottle and observe what happens next. Why did this happen?
6. Extend this activity with condiment packets like ketchup, mustard, mayonnaise, and any other packets you can find. Do you believe they’d all dive the same? Why or why not?

Science Behind it!

When you squeeze the bottle, the pressure on the water pushes on the pocket of air inside the plastic vile. You can see the level of the water in the diver rise as you squeeze the bottle . As the water level inside the diver goes up, it compresses the air above it into a smaller space. This demonstrates that gases are considerably more compressible than liquids. As the water level rises in the diver, it becomes less buoyant and the diver sinks. As you release the pressure on the bottle, the compressed air expands and forces the water back out. The diver floats to the top of the bottle because now it is more buoyant.

Extended Science!! Grab you other materials!!!!

Whether an object sinks or floats depends on if the total weight of the object is greater or less than the weight of the water it displaces. When a packet is just barely floating the parts that are less dense than water (air) are just barely canceling the parts that are more dense than water (package and ketchup). When you exert pressure on the bottle it is transferred to the air bubble within the packet, making it smaller, thus increasing its density. As this occurs, the packet sinks as the air no longer cancel the condiment. When you release the pressure, the bubble expands again, and the packet rises. Fish have an air sac within their bodies, and by controlling the amount of air in the sac, they use the same principle to rise and sink. Submarines also use this principle to dive and surface. Also, according to Pascal’s Law (also called Pascal’s Principle), pressure in a fluid is exerted equally throughout the fluid. No matter where you squeeze the bottle, at the top or at the bottom, the pressure will be exerted equally and the same diving effect will occur. The same principle is at work in a diver’s buoyancy compensation device (BC) or even your lungs at depth underwater. Release air from the BC (or your lungs), it will compress the remaining volume, and you sink. Add some volume (by adding more air to your BC or your lungs), and you will rise to the surface. Mastering these two skills are the ABCs of diving.