[Alex00087]

This has me so stumped... For my Honors Physics quarter project, we have to build a device that will sink to the bottom of a watertank and then all of a sudden float back up to the top in less then 30 seconds by itself. You are not allowed to help it at all. I have NO idea whatsoever how this is possible?

Anyone got any ideas on how to approach this? Maybe any engineers or scientists or anyone out there have any ideas? I would REALLY appreciate anything. Thanks.

[rampant]

How high can you drop it from?

[cjrivera]

Originally posted by Alex00087:
This has me so stumped... For my Honors Physics quarter project, we have to build a device that will sink to the bottom of a watertank and then all of a sudden float back up to the top in less then 30 seconds by itself. You are not allowed to help it at all. I have NO idea whatsoever how this is possible?

Anyone got any ideas on how to approach this? Maybe any engineers or scientists or anyone out there have any ideas? I would REALLY appreciate anything. Thanks.

Just once or several times?

[Alex00087]

The water/aquarium tank will be 10 inches deep. Device must be no taller than 7 inches.

[Alex00087]

Originally posted by cjrivera:
Just once or several times?

It just has to sink to the bottom once and then resurface once.

[xylon]

Hmm, from what I remember from physics, the question about how high seems the best start.

If you can figure out the bouyant force of your object, you can estimate about how much momentum/kinetic energy your object needs to have in order to get all the way down to the bottom of the tank. And as long as your bouyant force is great enough, once your object has hit bottom, it'll pop back up to the surface.

The forces you need to take into account are gravity, bouyancy and water (even air resistance if you really want to get picky) resistance...I think. It's been a while since I've had to think about things like Newton.

Hope that gives you some ideas.

[SupahCoolX]

Take a piece of styrofoam (or other floaty object). Hook on some weights to make it sink. There's a button/latch on the bottom of the styrofoam, so that when it hits the bottom of the tank, the weights get released and the styrofoam floats. Will that work?

[cjrivera]

Originally posted by SupahCoolX:
Take a piece of styrofoam (or other floaty object). Hook on some weights to make it sink. There's a button/latch on the bottom of the styrofoam, so that when it hits the bottom of the tank, the weights get released and the styrofoam floats. Will that work?

That's what I was thinking unless the whole device had to resurface.

[Alex00087]

Originally posted by cjrivera:
That's what I was thinking unless the whole device had to resurface.

Yeah unfortunately it says "you may not leave any part of your device on the bottom of the tank."

[fat mac moron]

Originally posted by Alex00087:
It just has to sink to the bottom once and then resurface once.

What about a balloon filled with a heafty amount of silicone? A salty solution in a filled baloon should surface. Think fake breasts, man!

[Sherwin]

I should state that I really have no idea but here goes anyways...

The fact that the brief states that it must rise within 30 seconds suggests that dropping something is not the required effect (because this would be much less?). Doesn't seem like dropping stuff into water is a suitable physics assignment for anybody over 12 either.

So are we looking at something to do with water pressure? i.e. as the object falls to a certain depth the water pressure triggers something to increase its buoyancy? Maybe an increase in air pressure inside the object? Maybe an increase in temperature inside the object?

Pressure seal breaks at a certain depth, lets exterior water into chamber with Lithium (etc.) in it, Lithium ignites to heat another sealed chamber in object?

Just ideas. I have no real clue!

[Sherwin]

Hmmm... Fill thermally inefficient object with ice, drop in near-boiling water? Ice rapidly melts (and thus expands) causing buoyancy?

[Alex00087]

yea except the aquarium wont have boiling hot water in it, thanks anyway though!

[voyageur]

Maybe a spear-shaped object, like a weighted pencil, that would knife through the water then bob to the top.

Or how about something weighed down with something water soluble?

[Sherwin]

Originally posted by Alex00087:
yea except the aquarium wont have boiling hot water in it, thanks anyway though!

Maybe try it with room temp water anyways - you never know! (the hot water will just speed the process - maybe you'll get under 30 seconds with normal temp. water)

[voyageur]

also,

perhaps find a substance (??) whose specific gravity is only slightly less than that of water's.

When this object is dropped, its momentum will overcome the slight difference in specific gravity, and cause it to sink to the bottom. Soon, however, the object will rise to the top.

[cdhostage]

An air bladder - empty balloon - with a piece of dry ice inside. You may have to put several balloons around each other to make sure the thing stays down long enough.

[xylon]

Focus on the physics man. Think about what you've learned in class and apply the principles. I'm assuming that you've learned about Kinetic Energy, Momentum as well as Buoyancy. You'll have to do some hairy calculations, but it is Honors Physics, and I think it's doable.

In my mind, you have to figure out the specific speed that the object will be travelling at when it hits the water such that it has enough momentum to overcome the object's buoyant force long enough for your object to hit the bottom. The buoyant force, however, must be enough to push the object back up to the surface.

Do they give you specific materials to use? And if they do, do they give you the coefficient of bouyancey for those materials? It's crucial to know those. You'll also need to know the mass of your object and it's speed at various stages of the drop. I hope this helps, again.

[tie]

edit

[Spliffdaddy]

hahaha

silly kids

the trick is to use baking powder.

It reacts with the water to form bubbles of air.

Years ago cereal boxes contained toy prizes. One of them was a submarine that would dive and surface over and over again - all you did was fill it with baking powder.

[Eriamjh]

Hmmm. Objects float because they weigh less than the water they displace.

If you don't go with baking soda, how about an object that expands slowly after it sinks, like a weighed sponge or sphere?

Isn't internet full of this kind of stuff?

[voyageur]

Originally posted by Spliffdaddy:
hahaha

silly kids

the trick is to use baking powder.

SpliffDaddy has it.

[BlackGriffen]

I actually like the dry ice idea best.

Baking soda and vinegar will work, too (I think baking soda and water will be too slow because the pH of tap water is only slightly acidic).

Pretty much anything that lets off gas/air will work.

BlackGriffen