Buoyancy Demonstration #1

[stevesrd]

Have you ever wondered how much energy it takes to raise a spoon back and forth from your plate of food to your mouth? Lets say you eat the plate of food in 10 minutes, now compared to how much energy you spent on bringing the food to your mouth, chewing and the like,,compared against how much energy that one plate of food will give you, do you get more then you give here? Is less energy burned eating that plate of food and more given from that plate of food? Think about it!

[hishouseinc]

One thing interesting about this is this shows that the water pressure allows the air to keep filling the jar even though the tube is still under water. That to me does not make since.

[TinselKoala]

It's the weight of the water, falling. When there's no way for air to get in, the water stays up at the top (really, the air pressure on the water in the pan keeps it there). As soon as there is any way at all for air to get in, even if the opening is under the water level, the weight of the water "sucks" air in until the pressure in and out are equal and the water level is the same in and out.

[hishouseinc]

What I am saying is, for the air to escape through the tube the water pressure has to be equal to the air pressure and that can not happen with the tube submerged 1 1/2 inches under water.

[Grafschnitzel]

If you would find a way to get the cork out from under the top vaccuum; then through it back into the water; and finally let it float up again in the glass - you would have a perpetual motion. Then do it with glasses of a mile high, and corks of 1000 tons, and you solve the world's energy problem.

[TinselKoala]

Why not just say, "if wishes were horses, beggars would ride"?

There are many classes of impossible devices that would solve the world's energy problems. Magic valves are just one example.

[Grafschnitzel]

Yeah, but why? What's the scientific argument? Check out my video reaction to Buoyancy Demonstration #2. Thanks for posting anyway!

[TinselKoala]

Are you asking "Why is it impossible to make a leakproof valve that will operate without friction, against a mile-high head of water pressure, and admit a solid object through it?"

Because materials aren't strong enough, friction losses cannot be eliminated, and you CANNOT get energy from a buoyancy drive even if you could solve these problems. Because for every cork you inject at the bottom, you are RAISING an equal volume of water, and this takes the same amt. of work you get back.

[NR22DLYPU]

this reaaly helps me thnx for rpostin this it helps me with hmewrk

[TinselKoala]

You're welcome. I hope your homework goes OK.

[UnderManiac]

To get the water to raise back up the jar, just suck the air out, reducing the air pressure.

[TinselKoala]

Try it.

Did it require an input of energy to "suck the air out?"

Yes, it did.

Because by doing so, you are LIFTING UP an equal volume of water. That takes work, and that's why buoyancy drives cannot operate.

And that's the point.

[UnderManiac]

I agree, energy needs to be introduced in order for the action to occur.

Just like he blew air into the jar to equalize the air pressure inside the jar as outside, thus lowering the water level, it would take sucking the air out of the jar, reducing the air pressure inside, to allow the water to climb back up.

[TinselKoala]

Almost. I didn't blow into the jar to equalize pressure. I just cleared the water out of the tube. If I had blocked the end of the tube so it contained only air, all I would have needed to do is unblock it. The weight of the water and the pressure of the air do the rest automatically.

[UnderManiac]

You can't forget the properties of air pressure. Yes water does seek it's own level. The reason the jar stayed full before you added air is because the bubble in the jar at the beginning was being pulled upon by the weight of the water in the jar, thus the air pressure of the bubble was much less than the weight of the water. Add more atmospheric pressure and the water level drops. Both systems, air and water are buoyant factors. Don't forget all the forces involved.

[Snuffelufugus]

Water seeks its own level???

I don't think you people have a fucken clue what you're talking about. Consider surface as an explanation for what you see.

[TinselKoala]

Can you speak English?

What do you mean, "Consider surface as an explanation?"

Do you mean something like "surface tension?" Then you may explain why liquids with extremely low surface tension behave exactly the same way, or why adding a surfactant doesn't change the buoyancy behavior. Surface-skimming insects and floating razor blades aren't kept up by buoyancy; this video is about buoyancy.

"Water seeks its own level" is shorthand for a bunch of stuff you probably wouldn't understand anyway.

[Snuffelufugus]

Yeah, I meant to write Surface Tension.

All fluid exhibit ST, possibly all substances, regardless of state. Surfactants don't treat the entire body of fluid, so they don't really change the fluid.

I'm trying to get my head around this too, but I could probably handle any explanation you had to offer. That is, as long as it doesn't rely on properties that are not well understood.

Why does a change in depth theoretically not require work, when we know darn well it's a change in P.E.

[TinselKoala]

OK, fair enough.

With buoyancy, the change in depth, changing PE, does require work. It's just that it only can return the work put into it, so the system can't work in a cyclic fashion without energy input. It takes work to sink a buoyant object, and the object returns the same work when it floats up.

When you sink an object, buoyant or not, you are raising the equal volume of water. This takes work. If the object is buoyant, it takes more work than the PE of height can provide (or return).

[Desertphile]

Great--- and thank you. There was a popular science magazine that asked its readers to explain why a column of salt water, with a permiable membrane at the bottom, would not produce a spout of fresh water when submerged in the ocean with the salt-water intake below the surface and the fresh water output slightly above the surface of the ocean. Since fresh water weighs less, some people believed it was possible. The readers explained why it is not, just as you have done so here.