6th grade science project

[iceman]

My daughter's supposed to build a submarine that will float for three seconds, sink to the bottom for three seconds, and then float again (three seconds minimum at each stage), or vice-versa. You can't touch the sub in the process. However you can modify the environment in which the sub sits. They've been studying buoyancy and density, so her idea is a balloon filled with room temperature water in a tub of room temperature water. It floats just barely (because of the natural buoyancy of the balloon, I suppose, plus there my be a tiny amount of air in there although we can't see it.

Theoreticallly, adding hot water should decrease the buoyancy of the balloon and it should sink.

Adding cold water (or just waiting until the temps in- and outside the balloon equalize) should cause the balloon to float again.

This should work, but it does not. It floats fine. Add hot water and the balloon sinks for a second but comes up to the surface well before three seconds pass. My guess is the water inside the balloon is heating up too rapidly, so that the cold water inside the balloon reaches or at least approaches equilibrium too fast. The only solution I can think of this is to use a larger balloon so that it will take longer for the temps to equalize. But using a big balloon means that the tubs of water have to be bigger and there's a limit to what she can tote around, heat up, etc.

Anybody have any solutions? The only thought I have right now is to insulate the balloon somehow, maybe with aluminum foil or something.

I could google it but I figured you geniuses might want something to do on a Friday.

[vinzclortho]

raisins sink and float in tonic water.

that probably doesn't really help in any way....but I thought I'd contribute

[DJSapp]

Balloon filled with sand and air so that it barely floats in a tub of hot water. Pour ice water on the balloon causing balloon to contract and sink. Balloon reheats, surfaces. Air is a better insulator, in theory is should take longer.

Worth a shot, or get one of these

[Core Shot]

You are creating gallileos thermometer.

Your problem may be the buoancy of the balloon itself.
Try using salt water of various densities inside the balloon to get a more neutral buoancy.

[Core Shot]

I guess they use metal weights for the Galileo deal
http://science.howstuffworks.com/question663.htm

[This End Up]

Most tricky to get it to sink then come back up. You could use water temperature change to sink it (Galileo example) then use salt to raise it again.

Make the sub just the right weight so that it floats on room temp water. Then heat the water, lowering the water density, and the sub should sink. Three seconds might be tricky though for heating the water. After three seconds on the bottom, add a enough salt to increase water density enough to make the sub float again.

[Big Blue]

Most tricky to get it to sink then come back up. You could use water temperature change to sink it (Galileo example) then use salt to raise it again.

Make the sub just the right weight so that it floats on room temp water. Then heat the water, lowering the water density, and the sub should sink. Three seconds might be tricky though for heating the water. After three seconds on the bottom, add a enough salt to increase water density enough to make the sub float again.

The salt is a great way to increase density of the water. Try alcohol to lower it. (probably should use denatured so you don't end up with a bunch of drunk sixth graders).

[Big E]

"First we add 5 shots of tequila. Following this, we then add a large portion of salt. We then top the balloon off with a dash of lime."

I'm sure there will be a parent-teacher conference to follow.

[Beaver]

Baking soda. Put it in a leaky heavy sub with a sealed top, sub fills with water and sinks, as the sub fills with water & the soda starts fizzing, sub continues sinking and hits bottom, fizzing continues until there is enough gas captured to lift the sub off the bottom. Ta da, magic.

[Buster Highmen]

Baking soda. Put it in a leaky heavy sub with a sealed top, sub fills with water and sinks, as the sub fills with water & the soda starts fizzing, sub continues sinking and hits bottom, fizzing continues until there is enough gas captured to lift the sub off the bottom. Ta da, magic.

Ding-ding.

[iceman]

Cool, thanks. I'm glad you guys are on your game, these will only get harder as we go along.

[Sensisnow]

How about a Cartesian diver:

Fill a 2 liter bottle with water.
Fill up an eyedropper with water until it barely floats on the surface in the 2 liter bottle.
Screw on the 2 liter cap.
Squeeze the bottle to make the eyedropper sink to the bottom, hold it for 3 seconds, then release to have the eyedropper surface again.

It should meet the requirements of the project and it's super easy and cheap to do.

[Stu Gotz]

You need to hire Stuart Little to drive the f@!#ker to the bottom and then re-surface.

[Dirty Hoar]

Get a can of Diet Coke which should float (regular coke will sink). Install a pattern of small holes over the majority of the tub bottom that air can be fed through. Place the diet coke in the tub and it will float. Turn on the air bubbles which should cause the diet coke to sink. Turn off the air bubbles and the diet coke should rise back to the surface.

I would suspect the easiest way would be the baking soda method but that's not very original. You can buy toy subs that do exactly that. (No offense Beaver)
It's basically one of many theory's of the burmuda triangle disappearances. Massive amounts of methane gas bubbling up from the sea bottom causing ships in the vicinity to loose buoyancy and sink.

[Stu Gotz]

It's basically one of many theory's of the burmuda triangle disappearances. Massive amounts of methane gas bubbling up from the sea bottom causing ships in the vicinity to loose buoyancy and sink.

You saw The Triangle this past week. Nice. Lou Diamond Phillips still has the mojo, no?

[Dirty Hoar]

No, I don't think so. Is that a movie? What I saw was on Discovery channel or something.

What's interesting is as the methane gas is escaping into the air it will cause aircrafts altimeter to go haywire. The methane gas is lighter than air so the altimeter will give you a false reading making it look like your climbing when actually your not. The methane gas could also cause the old radial(?) engines to quit in mid air sending the pilot to his doom.

Lou Diamond Philips reminds me of this guy that stole my little brothers money while we were sluffing school at my house. I had to kick his ass.

[Tippster]

Ah, Sargasso. The Loki of the Seaweed Edda.

[Dexter Rutecki]

Get a can of Diet Coke which should float (regular coke will sink).

I am pretty sure this is bullshit, unless there's some secret physical property Coca Cola has discovered and kept secret from everyone.

and edit to note that Wide Sargasso Sea was the first NC-17 movie I ever saw, and boy was I disappointed.

oh yeah, double edit to add that I think science labs such as the one assigned to ice's kid are basically a big waste of time. If there's a good way to do this, they should show the kids or have them do it--if they want them to figure out a way to do it, let them write a proposal, but all this building stuff/set-up is sort of glorified art or shop class. Personally I never had to see buoyancy or other concepts in action before understanding how they worked.

[Dirty Hoar]

Personally I never had to see buoyancy or other concepts in action before understanding how they worked.

Are you sure? http://news2.news.wisc.edu/whyfiles/071questions/5.html

[Oarhead]

Bring a big tub of water to the class. Also bring a snorkel. Get into the tub, swim around a bit, then dive to the bottom and hang out for 3 seconds before resurfacing.

Grade: 'A' mutherfuckin plus.


Just make sure you have a big enough pool. Your kid is worth it.

[Dexter Rutecki]

Now that's the idea, but I'm not sure why the snorkel is necessary as I bet Ice's kid can hold her breath for three seconds.

And I'm quite surprised, although I guess the explanation makes sense (and should be true for other sugary sodas?).

Are you sure? http://news2.news.wisc.edu/whyfiles/071questions/5.html

But you quoted the wrong part of my post...

[Tippster]

Now that's the idea, but I'm not sure why the snorkel is necessary as I bet Ice's kid can hold her breath for three seconds...

Style points. Critical in case there's a tie.

[Dirty Hoar]

But you quoted the wrong part of my post...

I use ACME's Random Quote Generator v1.4. It makes sense to ME.

[Dexter Rutecki]

OK, it makes sense to me now, too. You were being too clever for me (but seeing it still wasn't necessary).

[The AD]

I'm sure there's some clever way to use ice since ice floats. The water in the tub would cause the ice to melt, and if properly constructed, the sub to sink. The big challenge would be to get it to come back up to the surface. Maybe add salt to the water in the tub?