2 perfect spheres, same diameter, same weight...one aluminum, one steel. How can you tell them apart?

[presidentender]

Set them down and spin them with your hand, then stop them, again with your hand. The steel ball has greater rotational inertia (for reasons already discussed: more of its mass, proportionally, is concentrated further from its center), so it will feel like it fights harder against being stopped. Of course, it'll be harder to spin in the first place, too. Of course, this only works if the difference is such that you can notice it by hand; otherwise, you'll have to use a long slope, as before.

 

[JSSheridan]

I didn't read the thread, but since they inner hollow would be larger for the steel sphere. If you tapped on them and compared their frequencies, the higher frequency would be the steel.

 

[randay]

attempt to cut/scratch each sphere using an aluminum or steel knife.

 

[Howard]

Originally posted by: randay
attempt to cut/scratch each sphere using an aluminum or steel knife.

Good luck finding an aluminum knife, lol

 

[JTsyo]

The way it works in our office is that you find someone that has dealt with the spheres before and ask them.

 

[edcarman]

Originally posted by: silverpig

Originally posted by: LostUte

Originally posted by: edcarman

X-ray them - Al has thicker walls

That isn't how x-rays work. ...

I think he was saying you'd be able to see the sides of the walls...

That's correct. You use the X-rays to detect the air/vacuum cavity in the middle of the sphere.
I'm not sure of the exact physics of it, but I believe that the X-rays are reflected by the air-metal interface.
Differing material properties mean that you probably can't get an accurate measure of the exact value of the thickness without calibration, but you should be able to tell which is thicker by comparing them.

 

[Jimmah]

Way too much thought you're all putting into this. Easiest thing is to feel the metal, maybe lick it (oddly enough was a test we did in College), hell you could even be simple and smack the two together and see which one marrs.

 

[Modelworks]

Originally posted by: Jimmah
Way too much thought you're all putting into this. Easiest thing is to feel the metal, maybe lick it (oddly enough was a test we did in College), hell you could even be simple and smack the two together and see which one marrs.

Or if in a corporate environment, "What does upper management want each one to be ?"

 

[SlitheryDee]

If you strike both spheres with metal or stone at an angle the steel sphere will create sparks much more easily. The aluminum sphere may not spark at all, but regardless the difference should be easily noticeable.

 

[Kyanzes]

Easy. Over time the aluminum one will start to oxidize. You won't even have to touch the balls to tell them apart.

Edit: assuming the experiment is not time limited.

 

[silverpig]

Originally posted by: Kyanzes

Easy. Over time the aluminum one will start to oxidize. You won't even have to touch the balls to tell them apart.

Edit: assuming the experiment is not time limited.

Aluminum forms a native oxide that is maybe 2-3 nm thick and is transparent...

 

[mageslayer]

Originally posted by: KIAman
Hit each sphere and listen. The deeper sound should be the aluminum and the higher pitch should be the stainless steel.

I like this answer.

 

[cheesehead]

I know that aluminum starts developing magnetic properties if you make it cold enough. I'd wager that these properties are measurably different from those of stainless steel.

http://sprott.physics.wisc.edu/demobook/CHAPTER5.HTM

 

[QuantumPion]

You could put both spheres in a nuclear reactor. The neutron flux would activate nickle alloys in the stainless steel, transmuting them to Co-60 which gives off hard gammas. You could then give the spheres to your lab assistant and time how long it takes for him to start puking his guts out from the radiation exposure.

 

[cheesehead]

Originally posted by: QuantumPion
You could put both spheres in a nuclear reactor. The neutron flux would activate nickle alloys in the stainless steel, transmuting them to Co-60 which gives off hard gammas. You could then give the spheres to your lab assistant and time how long it takes for him to start puking his guts out from the radiation exposure.

Alternately, you could shave a bit off both spheres and combine them with ferric oxide and a bit of magnesium to start the reaction.

One is thermite. The other one is just magnesium stuck in some partially oxidized iron.

 

[bryanl]

Sniff them. Aluminum has a distinct smell that's easily noticed.

A more fun method: rub mercury on each sphere, and the aluminum one will show damage in a few days.

 

[Smilin]

Roll em both down a hill. The aluminum one will roll faster.

 

[BladeVenom]

Melt them. Steel has a much higher melting point.

 

[nevbie]

Cut them. Divide each one to two half-ball pieces. Then measure the wall thickness. The one which has thicker wall, is Al.

 

[Born2bwire]

Ooooh Oooh! I got another one. Grind them both up into dust and then mix in the requisite amount of iron oxide, apply a magnesium fuse to each mixture and the one that melts through the crucible and lower two floors of the building is the aluminum one.

 

[BladeVenom]

Chromatography

 

[videogames101]

Originally posted by: Born2bwire
Ooooh Oooh! I got another one. Grind them both up into dust and then mix in the requisite amount of iron oxide, apply a magnesium fuse to each mixture and the one that melts through the crucible and lower two floors of the building is the aluminum one.

That would go over well with the interviewer.

 

[Sho'Nuff]

Density

 

[KIAman]

Originally posted by: soxfan
Density

 

[Shadow Conception]

Why can't you just use d = m/v?