Submarine Project

[scifreak1123]

Hi!!!
I need a little help on my science project which is making a submarine out of household materials. It needs to float then sink, then float again. Please, THIS IS NOT A CARTESIAN DIVER!!!!!! If anyone has any ideas, please help me!
Thanks SOOOOOOOO much!
PS I can not use alka seltzer!

[OneBriiguy]

Hi!!!
I need a little help on my science project which is making a submarine out of household materials. It needs to float then sink, then float again. Please, THIS IS NOT A CARTESIAN DIVER!!!!!! If anyone has any ideas, please help me!
Thanks SOOOOOOOO much!
PS I can not use alka seltzer!

Hi, scifreak1123!

The experts in this forum work best when presented with specific questions about a science project. I think this would work best for you, too. I suggest that you try brainstorming some ideas of your own and come back to this forum with specific questions.

If you need to use household items, think about what you can find around the house that floats. If you had something floating on the water and you wanted it to sink, what would you have to change about it to get it to go under the water? What could you do that's reversable such that you could get it to come back up to the top?

Thank you!

[bradleyshanrock-solberg]

I've got no idea if this would work but attempting to follow the advice of the prior poster got me an idea like this:

get a pill bottle, put something like alka-seltzer in it that will generate bubbles when water hits it. Stick it to the top.

Put the pill bottle in the water, so air is trapped at the top with the alka seltzer...no water hitting it yet.

Tip it so water comes in and air bubbles out. It'll fill with water and sink.

Then the bubbles generated by the alka-seltzer will fill it with enough air to rise to the surface again.

No idea if that would work. But it's an idea of the kind of brainstorming you might want to do. It's fairly easy to make something that will float and then sink. The tricky part is to get it to rise up again. This means a way of adding air to the contianer somehow.

If it helps, real submarines have things called "ballast tanks". They take on water when they want to sink. They force the water out when they want to rise back to the surface (I think with compressed air, but I would have to research it, I've never needed to know exactly how). A submarine is designed to be pretty close to the "not sinking or rising" point most of the time. That's the kind of thing you're looking to do at home.

[Craig_Bridge]

Try doing a little research on bouyancy. You should try to understand displacements, mass, volume, density, ideal gas law, and neutral bouyancy priciples, and stability (does an object keep its orientation and right itself).

What constraints do you have? What size test tank are you going to use including what fluid (distilled water, tap water, something else). Are you allowed to put your hand down into the tank and cause some action or activation?

Take for example a 500 ml plastic quick disconnect syringe (no needle or tubing). Fill it with air, it will float. Push out the air, and the back end will fill with water and it may or may not sink. If it doesn't you could put in some weight in it to get it so it floats with air and the weight and sinks when the air is pushed out. Now the problem is how do you put air back into the syringe when it is under water. If you look at stability, the syringe will rotate about its long axis so it won't maintain its orientation. Obviously a 500 ml syringe is not a household item so you can't use this but it was the first thing I thought of to demonstrate something with a seal and piston to get you thinking.

If you compress a gas, it is denser so if you are close to neutral bouyant, you could alter the bouyancy just enough to change things. Take the 500 ml syringe and instead of leaving the end open and alowing the air to escape, seal it. When you depress the plunger, you compress the air and allow water to enter the back end so it will tend to sink. When you pull the plunger, you lower the air pressure and push water out the back end so it will tend to rise.

If you were to combine something like a can of compressed air and something like a two liter plastic beverage bottle you might be able to make it work in a similar way after you figure out how to add stability and let air out through the "top" and water in and out through the bottom and compressed air into the bottle to expel water out the bottom. Canned air might not be considered a common household item, so think about something like baking soda and vinegar that will produce CO2 as a "gas" generator to displace the water.

[OneBriiguy]

Since you need to make this project out of household materials, my guess is that you will need to keep this pretty simple. I liked the suggestion to study bouancy - why some things sink and others float. I also liked the syringe as an example of what might need to happen to make something sink or float. The reason it works for the syringe is the same as the reason changing ballast in a real submarine works - also mentioned in another post.

Can you answer the question why does ballast work? Think about ways that you can force water (ballast) in and out of a container - like a 2-liter bottle. If you put some holes in the bottle and put a balloon inside you can add and remove air from the balloon to change the amount of ballast in the bottle.

Other ideas?

[peteryoung]

Perhaps knowing more about the project's rules and limitations would
be helpful but how's this for another suggestion:

Develop a "diving chamber" that would be filled with some material that
would dissolve in water (salt or sugar may do).

If the rules allow it, do the following: fill the chamber with the
solid material and let the chamber first float, then fill with water through
vent holes. When enough water leaks in, the chamber would then sink to the bottom of the water tank. Then, after the sugar or salt dissolves and
is allowed to trickle out of the chamber, the chamber could then rise
to the top (as it could have air bladders that are competing with the solid material to achieve positive and negative buoyancy).

The basic idea comes from smugglers who drop contraband packages into the ocean, weighed down with salt blocks - and the packages rise up after
a certain time to be picked up. I saw this on TV, not gathered from personal experience


Peter Young

[bradleyshanrock-solberg]

Clever Peter. I like that one, if it's legal for the project.

Use ballast that dissolves in water and "falls out" once enough has dissolved....the bottle or whatever should then bob to the top.