Balloons and submarines have a lot in common. These experiments will show you how they work:
This experiment will let you see how a submarine dives and surfaces. It will also demonstrate how a diving bell works.
What you’ll need:
• A sink or bucket filled with water five inches deep
• A small (500 ml) empty plastic water bottle with lid (the kind you can crush easily)
• A bendable plastic straw
• Safety scissors
1. The instructor should cut a hole the size of a quarter on one side of the empty water bottle using safety scissors. The best way to make the hole is to pinch the bottle flat, then cut a semi-circle out of the edge. Keep the hand holding the bottle away from the safety scissors at all times when cutting.
2. Fill a sink or bucket with five inches of water.
3. Set the bottle in the water with the hole side down. It should float.
4. Now push the bottle to the bottom (keeping the hole side down) then bring it up again. Notice that water did not enter the bottle. This is because the bottle is filled with air, so there’s no room for any water to get in.
Why doesn’t the air escape? The air inside the bottle is a lot lighter than the water around it. That means that, just like helium, it wants to float upward. Since the bottle is surrounding the air on the top and sides, the air can’t move in that direction, so it stays trapped inside the bottle. A diving bell works on the same principle. The top and sides of the bell prevent the air from escaping in the direction it wants to go — up.
5. Now what happens if you turn the bottle so that the hole is facing up? The sides and top of the bottle are no longer keeping the air from moving upwards. You’ll see the air quickly float up and out of the bottle as bubbles. With all the air gone, there is now space inside the bottle, so it fills with water.
Submarines have something similar to the bottle called a ballast tank. When a submarine starts out on the surface, the ballast tank is filled with air. The tank acts just like a balloon, using a gas (air) that is lighter than the substance around it (water) to keep the sub afloat. To make the submarine dive, a hole on top of the ballast tank is opened. The air inside escapes, and the tank fills with water. The sub starts to sink.
Once your bottle is filled with water, let it sink to the bottom. This is like a ballast tank on a submerged submarine. So how do you get it back to the surface?
7. Place the bendable end of your straw in the hole. Now blow hard into the other end of the straw (which should be out of the water). The bottle shoots to the surface. A submarine ballast tank works the same way. To raise the sub, air is pumped into the ballast tank. This forces the heavy water out, and fills the tank with a substance (air) that is much lighter than the seawater around it. Like a balloon, this makes the sub float upwards.
This activity lets you learn the basics of flying gas balloons.
What you’ll need:
• Several helium-filled latex balloons (one for each racer)
• A narrow ribbon tied to each balloon (approx. four feet long, 1/4-inch wide)
• Small metal paper clips
• A clear indoor area large enough to accommodate a chaotic balloon race. Make sure the ceiling is low enough that escaped balloons can be recaptured.
The gas balloons used by Thaddeus Lowe were a lot like helium party balloons — sealed balls filled with lighter than air gas. To travel in a specific direction, Lowe would move his balloon higher or lower until he found an air current blowing the way he wanted to go.
Instead of a ballast tank, Lowe’s balloons used sandbags for ballast. The sandbags provided enough weight to keep Lowe from rising too high. If he needed to go a little higher, he could pour sand out of one of the bags to make the balloon lighter.
In this race, your goal is to be the first to fly your balloon across the finish line using nothing but your breath to blow it. Just like Lowe, you’ll have to put just the right amount of ballast on your balloon to keep it from flying too high (above your mouth, where the wind is) or too low. If you find the sweet spot — right at the level of your mouth when you’re standing up — you’ll be able to blow your balloon faster.
Each participant gets a balloon with a three to five foot string or ribbon tied to it. Make sure to do this activity indoors, in a room where the ceiling is low enough that you can get your balloon back if it escapes.
First let go of your balloon. Notice it flies to the ceiling. This is far above where the wind is (your mouth). To lower your balloon, start adding small paperclips to the ribbon tied to it. The trick is finding the right amount of ballast to keep it near your mouth.
Once everyone is ready, go to the starting line. Each racer should let go of his or her balloon. Remember, don’t touch the balloon with any part of your body — use only your breath to move it. Have someone say “go” and you’re off.
How did you do? Do you think your balloon should be higher or lower? Adjust the ballast. Do you think a different method of blowing would have worked better? Try it on the next race.