Chemistry

[zee2307@aol.]

what can you put in a can and make the can weigh less

[squarebear]

Helium or Hydrogen. As this is lighter than air, the can will weigh less.

You could also put a hole in it. That would do the job! :o)

[Skreecheeboy]

Helium or hydrogen would both work but I think the answer you are looking for is a straw, thus enabling you to remove the contents by sucking.

[Skreecheeboy]

Damn you square bare, the hole is even simpler than the straw!

[Skreecheeboy]

Jings, please don't take that the wrong way Square bare, I'm more annoyed with myself.

[squarebear]

lol no worries. I was just having fun with the hole.

[squarebear]

Ah but helium or hydrogen would give the can a bit of lift, which would decrease its weight even more than having a vacuum inside.

[mibn2cweus]

. . . H and He weigh less than nothin'???

[squarebear]

No but they weigh less than air and so will try to raise the can up. A vacuum will leave the can standing.

[chakka35]

mib is right, of course. No gas at all will weigh even less than hydrogen.
But you couldn't do it in practice. Suck all the air out of a can and the 15lbs of atmospheric pressure acting on every square inch of the can's surface would crush it.

That's why you can't have vacuum balloons. Any casing strong enough to withstand the outside pressure would be too heavy for the vacuum to lift!

[squarebear]

But the question was to make the can weigh less not the contents. Helium or better still, hydrogen, would make the can try to rise in the air and so reduce the weight of it.

Is it only me that can see that?

[mibn2cweus]

Technically contents have no bearing on the net weight of the can itself which is determined entirely by the mass of the material from which the can is constructed, the force of the gravity field where it is located and the buoyancy of the surrounding medium both inside and out.

An aluminium can would float in a bath of mercury even if it were completely filled with the same mercury.

[mibn2cweus]

Correction:

Buoyancy contributes an error of "false weight". The actual weight of the can would be as weighed empty in a vacuum. Any content added would be the weight of the contents and not the weight of the can itself.

[jadyn]

I don't understand tonyted.

Your first sentence appears to contradict your second sentence.

Let me put it like this. You appear to say that if I cut a 2 inch diameter hole in such a can with a rotary holesaw, the can's weight would not decrease?

Sorry, but I can't see how your assertion can be true even if we are now entering the realms of the difference between mass and weight.

[newtron]

jadyn, it is possible to poke a hole in a can without rmoving mass.

[newtron]

That is without removing mass.

[jadyn]

newtron, perhaps I didn't make myself clear.

When I said about cutting a two inch hole in the can with a rotary holesaw, I assumed the reader would surmise that the resulting disc would be removed from the can.

I did not say anything about "poking a hole" in the can.

The difference between cutting a hole in the can and removing the disc and poking a hole in the can should be evident. In the first case, we are removing part of the matter of which the can is composed, whereas in the second scenario, we are not.

Mass is the amount of matter present in a given body. When we remove the disc from the can, we are removing part of the matter of which the can is composed. Ergo, we are decreasing the total mass of the can.

Given that we are working on the assumption that the can is on Earth undergoing conventional gravimetric effects, removing part of the mass in this manner will decrease the weight.

The only circumstance under which tonyted's assertion that "nothing would make the can weigh less, not even a hole" would be true would be if every single particle affected by the making of that hole remained on or in the can. I agree that poking a hole in the can would allow this to happen, but you'll note that tonyted failed to explain that this was the only method and circumstance by which the mass would be unaffected. If tonyted had poking in mind when he thought of the hole formation, he should have said so. After all, holes can be drilled out, cut out with welding equipment etc and in these circumstances, the mass of the can would be affected as I said.

[newtron]

jadyn, you made yourself perfectly clear. I was just giving tonyted the benefit of the doubt and assumed that he understood what mass and weight were. Therefore, I figured he was talking about poking a hole in the can. As you said he didn't specify the method by which the hole was being made. So you made the assumption that he was talking about making a hole in a way that did remove mass from can, as that is the only way that his first sentence would appear to contradict his second sentence. Because he didn't make it clear how he intended to make a hole in the can, it probably would of been better to ask him what he meant instead of accusing hi of contradicting himself.

[jadyn]

newtron, asking tonyted what he meant would have proven to be a pointless exercise. Since that post, he's not made any further input to this question so an answer would not have been forthcoming.

As far as assumptions go, you've assumed that a poster will continue to read the thread for as long as necessary and reply to any questions directed at him or her. I've been on here long enough to realise that's not always the case as tonyted has illustrated.