Puzzle: You have to chose between two cylinders.

gong! bong! tong!

I like it, I like it...

Me, I'd have spun it. The hollow cylinder will have more angular momentum... More mass out at the ends.

Spinning the cylinders might determine which had one or more hollow places, but that might not be the gold if the the other cylinder was made of osmium or platimum both of which have a higher density than gold. tungstan is minutely less dense at 19.3 Most gold has some metal alloyed with it so about 19 is typical If the density of both cylinders is 19.32, then you can be sure the gold cylinder has no hollow spaces, and likely negligible lighter alloying metals. A third cylinder that you know is gold, should produce the same sound as the other gold cylinder, when you tap it. These will not work if the mesured density is less than 19.32 at 20 degrees c = 68 degrees f as you won't know where the hollows might be. unless you x-ray the cylinders. If the cylinders are more than a few milimeters in diameter you will need to use gamma rays from an isotope to make the radiographs. Simpler would be to bend the cylinders. the one requiring the least bending force is likely the gold as most other heavy metals are more rigid than pure gold, but that is not for sure either. Neil

The two cylinders
Use a mallet to tap each of the cylinders. As the gold cylinder is hollow, it will sound with a different resonance than the solid one.

Spinning would work, The problem says that the cylinder is "solid" and that both cylinders have the same "weight" (or more properly mass).

The moment of inertia will be higher for the gold cylinder. Just spin both with equal torques(i.e. same force at the same distance from the center). The gold will end up spinning slower.

Maybe you could disolve the paint.

If you couldn't, then maybe you could put them into a Metal-Sulphate substance and see whether a redox reaction takes place.

First off, if a bumblebee's flight is against the "laws" of aerodynamics, that's BAD science because science takes into account observable fact. Therefore I conclude that whatever "laws" of aerodynamics to have declared such rubbish as POPPYCOCK.

Anyway... I like neil's answer because it demonstrates how the rest of the world probably sees scientists. Lots of facts and very little information. aka "trying to sound smart" (my family accuses me of this all the time)

I don't think crunch got the initial conditions right.... and I just noticed that I think the answer (well, a possible answer) was already posted by the poster.

I was going to say check their bouyancy, maybe in oil, but that wouldn't work because if they had the same size and weight, they would have the same density. Uhh... is the paint conductive?

My other guess would have been to use a magnet... it would not react to a "non-magnetic" alloy, while gold, being HIGHLY conductive, should 'stick' to the magnet.

Do magnets 'stick' to gold? I'll go check...

mm...my first reaction was put them in water...coz i though even though they have the same mass - the gold still has air.....

another thought was magnets im pretty sure that gold isn't magnetic...so that may work too..

First heat them to the same temperature then leave for some time and measure the temperature.

Heating the cylinders is a great idea! The values of specific heat and conductivitiy for gold are well known. The only problem is the paint - but I think you could convince yourself this wasn't significant.

Any idea that involves floating (in water oil or anything else) will not work. Whether and how much an object floats (i.e. its bouancy) is determined by its weight and its volume.

Since the two objects have the same weight and the same volume they will float exactly the same in any substance. The fact that one has "air" is irrelevent.

Re: Puzzle: You have to chose between two cylinders.


I don't think it's possible for two different materials to have the exact same densities. Unless they're both made of gold...but gold is not an alloy...

Re: Puzzle: You have to chose between two cylinders.
While the two "materials" may not have the same density, the density of the two objects may be the same. The hollow gold cylinder will have a density much less than that of solid gold.

Of course the densities of two substances can be the same, especially with an alloy. An alloy is a mixture of two metals (presumably with different densities). You can just adjust the amount of each metal untill you reach density you want. You can also adjust the density a bit simply by changing the temperature.

The problem states that the cylinders have the same size and the same weight. This would mean the substance of the hollow tube would need a density much *greater* than the non hollow one. (in the problem the word "density" refers to the density of the cylinder and not of the substance).

If you want to distinguish the two cylinders by density -- How do you intend to measure the densities of the cylinders?