# Up Periscope or Down?

Medium
##### Cost

Less than \$10.00

##### Safety Issues

An adult should make the necessary cuts in the plastic liter bottle. To prevent drowning, young children should not be left unattended around water.

##### Material Availability

Plastic tubing is available at a hardware story. The remainder of the materials is readily available or easily purchased at a grocery store

##### Approximate Time Required to Complete the Project

An hour to complete the project and collect the data; a day to prepare the science fair display

### Objective

To investigate how a submarine sinks and surfaces by exploring the density of water and air

### Materials and Equipment

• 1 empty 1-liter plastic bottle
• Sharp knife (for adult use only)
• 4 quarters or thick washers
• 18 inch plastic tubing
• Small ball of modeling clay
• Large tub
• Water

### Background Information

Water is denser than air. A submarine sinks and surfaces because of a mechanism that allows the displacement of water and air. When water is forced into a chamber, the submarine sinks. When the water is forced out of the chamber by air, the submarine surfaces. To keep the submarine at a constant level, the chamber maintains a balance of air and water.

In this investigation, a model of a submarine is built to simulate the buoyancy and displacement of water and air.

### Terms, Concepts, and Questions to Start Background Research

##### Terms

density: how heavy something is for its size

buoyancy: the force that causes something to float

displacement: the exchange of space between one substance by another

##### Concepts

Water is heavier than air. When a submarine is filled with water, it sinks. When the water is replaced with air, it floats to the surface.

##### Research Questions

How does a submarine sink? How does it resurface?

### Experimental Procedure

1. Gather the necessary materials.
2. Have an adult cut three ¼ inch holes in the side of the liter bottle. The holes should be lined up and space about 1 ½ inches apart.
3. Tape the washers between the holes.
4. Push the plastic tubing through the ball of modeling clay. Then use the modeling clay to seal the opening of the plastic liter bottle. The plastic tubing should have one end inside the bottle and a long piece outside the bottle.
5. Fill the tub with water. The water should be deep enough that the bottle can be completely submerged.
6. Lower the bottle slowly into the water, keeping the bottle horizontal (on its side) and the plastic tubing out of the water. Observe and record what happens.
7. Blow air into the plastic tubing. Observe and record what happens.
8. Repeat steps 6 and 7. What do you observe?

### Bibliography

##### Articles

“How Submarines Work” by Marshall Brain and Craig Freudenrich, Ph.D at http://science.howstuffworks.com/submarines.htm

“How Does a Submarine Work?” by Ajay Dasgupta at www.pitara.com

“Underwater Dream Machine” at PBS Video

##### Websites

Museum of Science and Industry at www.msichicago.org

##### Books

Thomas, Isabel. Dive! Dive! Dive! Raintree Publishers, 2007.

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