Buoyancy Lesson

What keeps this scientist from floating to the surface or even sinking to the bottom?

Scientists who study underwater have a challenge to stay in one place to conduct their work. Here's an experiment you can do to find out how they do it.

Ping Pong Divers

Directions:

1. Use your pencil and paper to record all of your observations and answer any questions when necessary.

2. Take your glass or cup and fill it about 2/3 full of water. Mark the water level with a piece of your tape.

3. Now, place a ping pong ball in the water. What happens to it?

4. Push down on your ping pong ball. What do you feel? What happens if you quickly let go?

5. Push down again until 1/2 of the ping pong ball is under water and look at the water where you marked the water level with tape. What happens to the water level?

6. Tape a dime to the ping pong ball with your tape and return it to the water. Does it still float?

7. Find out how many dimes you need to tape to it before it sinks. Write that number down.

8. Once the ball is at the bottom of the cup or glass, look at your water level again. Why is it higher than before?

You Be The Scientist:

1. Write down what you think will happen if you put the golf ball or marble in the cup of water. (Hypothesis)

2. Try it. (Experiment)

3. Write down your observations. (Observations)

4. What happened? Why do you think that happened? (Conclusions)

Connecting to Aquarius:

So, how do divers stay at a constant depth?

Scientists working on Aquarius conduct much of their research out on Conch Reef. Of course, they have to leave Aquarius and go out to the reef itself. Divers use two devices to achieve what is called "neutral buoyancy." Neutral buoyancy means a diver is neither sinking nor rising to the surface. To achieve this a diver must take into account several factors:

• Their weight and percentage of body fat
• The thickness and type of dive suit they're using
• The type of air tank they're using
• The weight or buoyancy of equipment they carry

To achieve neutral buoyancy, divers use a weight belt to add weight to themselves and counteract their tendency to float to the surface. But what if they're too heavy? Divers also use a buoyancy compensator or BC to which they can add air if needed making them more buoyant. It is important that reef scientists don't sink and step on the corals they're studying!

If you fill a balloon with air and put it underwater it will float to the top. Aquarius is full of air! Why doesn't it float up?

Aquarius weighs about 80 tons in the air but is almost neutrally buoyant in water. It is attached to a base plate that weighs 120 tons, so it stays firmly anchored to the ocean floor. The base plate supplies the extra weight (like the diver's weight belt) to hold it down under water.

Find Out More:

Try this activity out to see how a ship that weighs several tons can stay afloat. Click Here!

Try these buoyancy math problems! Click Here!

Find out why Buoyancy was important to a young man named Archimedes at Britannica Online.
Lesson design by Lucas Gillispie