xkcd

by **qinwamascot** » Fri Nov 14, 2008 6:48 pm UTC

Shoot a rocket to the moon normal to then earth's surface. Drop a feather off at the moon, then return the rocket. Measure the change in earth's angular frequency. It's pretty trivial really. If you want to get fancy, we could shoot feathers through a diffraction grating and measure the interference pattern.

by **Hydralisk** » Sat Nov 15, 2008 10:55 pm UTC

I see...

In that case (sorry if this has been mentioned too!) couldn't you just a) figure what the feather was made of (carbon mostly presumably) b) Calculate the number of atoms/molecules in said feather using Avogadros' number etc.? [/not-a-chemist] c) Figure out the weight from that?

Or Put the feather on a Newton scale in a vacuum, remembering to neglect any quantum effects?

[Probably been mentioned before, but I can't find anything in my brief skim of the forums.]

by **Cynical Idealist** » Sat Nov 15, 2008 11:26 pm UTC

Hydralisk wrote:In that case (sorry if this has been mentioned too!) couldn't you just a) figure what the feather was made of (carbon mostly presumably) b) Calculate the number of atoms/molecules in said feather using Avogadros' number etc.? [/not-a-chemist] c) Figure out the weight from that?

The problem with trying to figure out the weight from the number of molecules in a feather is that the number of molecules is generally found by looking at the weight*, making that solution circular at best.

*If I'm remembering my basic chem right...

by **smw543** » Sun Nov 16, 2008 2:06 am UTC

Cynical Idealist wrote:The problem with trying to figure out the weight from the number of molecules in a feather is that the number of molecules is generally found by looking at the weight*, making that solution circular at best.

*If I'm remembering my basic chem right...

Yes, that is the usual way (only replace the word "weight" with "mass.") To avoid the circularity, the obvious solution is to count the individual molecules one at a time, perhaps with the use of very small tweezers. Of course, this procedure must be done in a vacuum, and the tweezers must be composed of a nonreactive material (ideally adamantium or diamondillium, but if you're limited to materials that actually exist, there are several other options) in order to avoid the observer effect.

by **Cynical Idealist** » Sun Nov 16, 2008 2:17 am UTC

smw543 wrote:
Cynical Idealist wrote:The problem with trying to figure out the weight from the number of molecules in a feather is that the number of molecules is generally found by looking at the weight*, making that solution circular at best.

*If I'm remembering my basic chem right...
Yes, that is the usual way (only replace the word "weight" with "mass.") To avoid the circularity, the obvious solution is to count the individual molecules one at a time, perhaps with the use of very small tweezers. Of course, this procedure must be done in a vacuum, and the tweezers must be composed of a nonreactive material (ideally adamantium or diamondillium, but if you're limited to materials that actually exist, there are several other options) in order to avoid the observer effect.

I don't know, that seems like it would take too long. I favor colliding the feather with an anti-feather and measuring the energy released, as suggested much earlier in the thread.

by **rho** » Sun Nov 16, 2008 1:52 pm UTC

smw543 wrote:...To avoid the circularity, the obvious solution is to count the individual molecules one at a time, perhaps with the use of very small tweezers. Of course, this procedure must be done in a vacuum, and the tweezers must be composed of a nonreactive material (ideally adamantium or diamondillium, but if you're limited to materials that actually exist, there are several other options) in order to avoid the observer effect.

Why not simply use a STM to count the individual atoms? It could move them about one by one. It would take a while, sure, but that's all right, bring a book with you and I'll put the kettle on.

by **Diadem** » Sun Nov 16, 2008 3:13 pm UTC

Wow, these methods are all so complex.

The easiest way of getting the mass of a feather is of course to throw it into a black hole, and measure the change in Schwarzschild radius of the black hole. The change in Schwarzschild radius will be directly proportional to the change in mass of the black hole, and thus to the mass of the feather.

Of course you need an isolated black hole with no other mass infalling, and you need to make sure the kinetic energy of the feather is zero as it passes the event horizon. Oh and of course take into effect the mass change due to CMBR and Hawking radiation.

by **Hydralisk** » Sun Nov 16, 2008 5:32 pm UTC

I wouldn't normally endorse this, but I'm just going to ask Jesus.

by **MotorToad** » Sun Nov 16, 2008 8:39 pm UTC

Have Jesus turn it into wine, then drink it and measure your BAC. Easy peasy.

(Assuming Jesus transmogrifies things according to the laws of thermodynamics.)

by **wst** » Sun Nov 16, 2008 10:01 pm UTC

MotorToad wrote:Have Jesus turn it into wine, then drink it and measure your BAC. Easy peasy.

(Assuming Jesus transmogrifies things according to the laws of thermodynamics.)

Why wouldn't he, he's the son of an omnipotent superbeing who made a virgin give birth, and still regularly thousands of people scream his fathers name in either ecstasy or agony. If I was one of those, I'd obey thermodynamics, and disobey other laws, just to fuck with atheist's heads.

by **ArmonSore** » Sun Nov 16, 2008 10:02 pm UTC

MotorToad wrote:Have Jesus turn it into wine, then drink it and measure your BAC. Easy peasy.

(Assuming Jesus transmogrifies things according to the laws of thermodynamics.)

Thermodynamics asserts the conservation of energy. It does not assert the conservation of fishes and loaves.

by **niteice** » Mon Nov 17, 2008 6:48 am UTC

ArmonSore wrote:
MotorToad wrote:Have Jesus turn it into wine, then drink it and measure your BAC. Easy peasy.

(Assuming Jesus transmogrifies things according to the laws of thermodynamics.)

Thermodynamics asserts the conservation of energy. It does not assert the conservation of fishes and loaves.

e=mc^2

by **Big Al** » Wed Dec 10, 2008 4:29 am UTC

You could weigh the body of a dead bird on s sensitive scale, remove ten feathers, weigh again and divide difference by 10?

by **Scythe of Vyse** » Wed Dec 10, 2008 7:52 pm UTC

I would say that mass of feather is far less the body weight of bird, and I think there should be some co relationship between body mass and feather. Do you guys agree?

by **V4mp** » Wed Dec 10, 2008 8:37 pm UTC

Personally I'm all for sticking the feather in a mass spectrometer to determine the relative concentrations of molecules in it - then you simply take an identical feather (preferably the same one - perhaps someone with a more complete knowledge of physics can come up with a little wormhole to retrieve it from the past, before it was mass-spec'd) Then all you'd have to do is count the number of moles of one substance in the feather through a forced complete reaction - perhaps by reducing the feather to an environment of absolute 0, thereby separating all the atoms, then heating it and reacting all the carbon atoms with excess Oxygen under an infinite pressure. Now you know the number of moles of carbon atoms in said feather - simply use this and some simple ratios from the mass spec results to calculate the actual amount of moles of all the molecules. Then you can use this and the relative formula masses to get the mass of each of the molecules within, and add them. tada, mass of one feather

Unfortunately this requires an assumption of an average distribution of all common isotopes of atoms in the feather - so if your birds been anywhere near an unstandardised area, and taken up one to many carbon 13 atoms it'll fall to bits

Also i'm surprised everyone has kept faith in the success of the clearly sub-standard calculators you'll be using to determine this feather - think of all those lost decimal points! you may as well just guess at the mass with such huge percentage errors left by such obscene rounding. Clearly the first thing to do is develop a superconducting computer with infinite memory to store all these calculations

by **Senefen** » Thu Dec 11, 2008 3:59 am UTC

I'm not sure if I'm impressed or worried that we have 4 pages of this. I am amused though.

Vapourize it, stick the whole thing in a mass spectrometer and add up all the mass signals. Take into account contamination.

by **BlackSails** » Thu Dec 11, 2008 4:53 am UTC

Put a known number of feathers in a giant cluster, then use the velocity dispersion and virial equation to solve for the mass of all the feathers.

by **benfr** » Thu Dec 11, 2008 10:45 pm UTC

Completely burn the feather in oxygen and measure the mass of the products (EDIT: And the change in enthalpy). Use the mass to determine the number of moles of each produced. Then using Hess' Law and the enthalpy of formation of the products calculate the enthalpy of formation of the feather, and hence the mass of the feather.

by **BlackSails** » Thu Dec 11, 2008 10:52 pm UTC

benfr wrote:Completely burn the feather in oxygen and measure the mass of the products. Use the mass to determine the number of moles of each produced. Then using Hess' Law and the enthalpy of formation of the products calculate the enthalpy of formation of the feather, and hence the mass of the feather.

How do you know the mass of the products? You have all sorts of gaseous things that will escape. CO, CO2, various NOx, etc.

by **benfr** » Thu Dec 11, 2008 11:01 pm UTC

BlackSails wrote:
benfr wrote:Completely burn the feather in oxygen and measure the mass of the products. Use the mass to determine the number of moles of each produced. Then using Hess' Law and the enthalpy of formation of the products calculate the enthalpy of formation of the feather, and hence the mass of the feather.

How do you know the mass of the products? You have all sorts of gaseous things that will escape. CO, CO2, various NOx, etc.

COMPLETELY burn = no CO.

Plus whats to stop you separating them and then measuring? They have different densities, melting/boiling points, etc. There are thousands of ways to separate them.

by **odenskrigare** » Thu Dec 11, 2008 11:37 pm UTC

From an albatross or swallow? African or European?

by **Gammashield** » Thu Dec 11, 2008 11:44 pm UTC

An *average* feather, of course.

Which means we need merely repeat the above procedures on feathers from every type of bird, add them up, and then divide.

by **alexh123456789** » Fri Dec 12, 2008 12:06 am UTC

Don't forget to weigh your average according to how many birds there are of each species and how many feathers each has on average

by **MotorToad** » Fri Dec 12, 2008 12:57 am UTC

To get the most accurate measurement, you'd have to do this in space. You know, to get rid of that pesky variance in g at different places on the Earth's surface.

weight = mass * g

m = w/g where g = 0. Mass is undefined.

Problem SOLVED!

by **3clipse** » Fri Dec 12, 2008 12:58 am UTC

Citizen K wrote:
What is the mass of a feather?

In ancient Egypt...
One soul, more or less.

And I remember some reading about some scientist or another who once tried to weigh souls as they escaped dying people (don't remember all the details offhand). So find those numbers and use them. Or go collect your own data. "Now hold still. Remember, it's for science."

They used a really heavy feather though, had it made up special (cookie to whoever gets the reference).

by **Tyr_oathkeeper** » Sat Dec 13, 2008 3:44 am UTC

1. Find a witch
2. A witch floats and a duck floats
Therefore mass_witch = mass_duck
3. Subtract the mass of a duck that is missing one feather from both sides. (Life insurance is advised, in case this kills the witch)
4. ???
5. Profit.

by **monkeykoder** » Fri Jan 02, 2009 9:53 am UTC

Obviously none of this can be done until we have a complete and consistent axiom system for our mathematics. Of course once we've accomplished this we will be gods therefore we will be omnipotent so we can make ourselves omniscient and we'll just know the answer. Sheesh why has no one thought of this before.

by **Diadem** » Fri Jan 02, 2009 6:10 pm UTC

Ok, here's how you find the mass of a feather.

First, assume a feather is a perfect sphere ...

by **cpt** » Mon Jan 05, 2009 3:09 am UTC

Why don't we just ask the feather?

by **Rippy** » Mon Jan 05, 2009 5:42 am UTC

Cynical Idealist wrote:
Hydralisk wrote:In that case (sorry if this has been mentioned too!) couldn't you just a) figure what the feather was made of (carbon mostly presumably) b) Calculate the number of atoms/molecules in said feather using Avogadros' number etc.? [/not-a-chemist] c) Figure out the weight from that?

The problem with trying to figure out the weight from the number of molecules in a feather is that the number of molecules is generally found by looking at the weight*, making that solution circular at best.

*If I'm remembering my basic chem right...

You could, if you knew the volume of the compounds that it's made of, put a bunch of feathers in water, measure the volume change, and divide by the number of feathers you threw it (for accuracy's sake many feathers are used). But feathers seem like they'd keep air bubbles stuck to them...

by **gavinski91** » Sat Mar 07, 2009 12:06 am UTC

Mathmagic wrote:This thread reminds me of the riddle:

What weighs more; A pound of feathers or a pound of bricks?

You'd be surprised how many people choose the bricks.

With regards to weighing the bowl of feathers:

I think the buoyancy of air would have too much of an effect on that measurement, no? Unless you bounded all the feathers together...

but keep in mind that a pound of feathers weighs more than a pound of gold.

by **Anubis** » Sun Mar 08, 2009 4:18 am UTC

Well, you just give the barometer to the janitor and...

Wait, wrong problem. :oops:

by **VorpalSword** » Sun Mar 08, 2009 5:22 pm UTC

To measure it we simply need to get the feather far enough away from any other large gravitational bodies, then measure the amount of warping it does to space time. The easiest way to measure the mass though, would be to design a new system of measurement, here the base unit = 1 feather (a feath perhaps?)

by **canoemoose** » Fri Mar 13, 2009 3:21 pm UTC

You're all wrong. You heat the feather with a known amount of energy. Using E=mc \Delta \theta and looking up c, the specific heat capacity of a feather in one of those huge books of tables of stuff like that, you can find the mass of the feather from m= E\over c \Delta \theta

EDIT: Hmm, I can't seem to make the TeX "\over" bit work properly.

by **Forum Viking** » Tue Mar 17, 2009 6:33 am UTC

I believe the proper way would be to compress the feather using nuclear fusion into one largish atom, which you then put into a perfectly sized (for this atom) container containing a perfect vacuum. Then you find the pressure exerted by the single atom using the ideal gas law since no other atoms would cause interference.
P= measure it
V=xL
n=1/(6.022*10^23)
R=.08206 or however accurate you want it to be
T= 298 K so we don't have to wear jackets when we do the experiment
PV=nRT

So you know the volume of your feather. Fusionize a bunch of water and pressurize, etc to the same point as teh feather=atom. Use the known atomic weight of water to find how many moles it took. Use the atomic weights of protons, electrons, and neutrons to find how many there are of each and assume that is the same amount for the feather. Then add them up.

by **meat.paste** » Tue Mar 17, 2009 6:41 pm UTC

No, no, no. The answer is easy and obvious. Define the mass of the feather to be 1 unit of mass. Finished.

(It's someone else's job to calculate the conversion factor into other units.)

by **The_Duck** » Wed Mar 18, 2009 9:36 am UTC

Simply synchronize two precise clocks, then put one clock next to the feather and the other far away. After some time, bring them back together and determine the amount of time dilation due to the feather's gravitational field. From the time dilation compute the mass.

by **Pazuzu** » Wed Mar 25, 2009 9:19 am UTC

Obviously you can't weigh feathers to find mass, as weight != mass. They don't even share any letters. I suggest one builds a mass measuring device rather than use a weight measuring device.

However, I think the easy solution lies in that we're seeking the mass of an average feather. Earths mass - the mass of all non-average feathers = mass of all average feathers. Then make a count and divide.

by **Kadzar** » Wed Mar 25, 2009 2:12 pm UTC

smw543 wrote:Negative mass, you say? That arises the obvious question of how? I propose that there is some sort of graviton, only opposite; an antigraviton, if you will (yeah, I know, just hear me out.) This is a particularly utile notion in that it finally solves the bumblebee problem; although they are too heavy to fly, their antigraviton glands allow them to defy those calculations and spit in the faces of apiarists and entomologists everywhere.

To the Nobel Committee, contact me by PM about my soon-to-be historic "sweep," winning the Prize for physics (for developing the antigraviton,) physiology (for furthering knowledge of the "antigraviton gland",) chemistry (due to the rapid advancements allowed by my discovery,) and literature (for this beautifully crafted post.)

Building off of your hypothesis, I propose that birds must secrete a type of antigraviton substance into their feathers, which is why feathers are so well suited for use as pens: they are obviously adapted to absorb and expel this substance. It is no small coincidence that those birds whose feathers make for the best quills are also excellent fliers.

by **smw543** » Wed Mar 25, 2009 5:32 pm UTC

Kadzar wrote:Building off of your hypothesis, I propose that birds must secrete a type of antigraviton substance into their feathers, which is why feathers are so well suited for use as pens: they are obviously adapted to absorb and expel this substance. It is no small coincidence that those birds whose feathers make for the best quills are also excellent fliers.

This would also explain how Keats wrote such lofty poetry - he used a quill!

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