A plumber wrote to the Bureau of Standards saying that he had found
hydrochloric acid good for cleaning out clogged drains.  The Bureau
write back 'The efficacy of hydrochloric acid is indisputable, but 
chlorine residue is incompatible with metallic permanence'.  The plumber
replied that he was glad the Bureau agreed.  The Bureau tried again,
writing 'We cannot assume responsibility for the production of toxic
and noxious residues with hydrochloric acid, and suggest that you use
an alternate procedure'.  The plumber again said that he was glad the
Bureau agreed with him.  Finally, the Bureau wrote to the plumber
'Don't use hydrochloric acid; it eats hell out of the pipes'.
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A physics major, a chemistry major, and an economics major are on an
an island with only canned food and no can opener.

Physics major:  Drop the can from a tree.  The can will accelerate until
reaching the ground, at which point, the can will decelerate, causing the
sides of the can to buckle, and the energy will be transferred to the lid,
and cause the lid to fly off.  The entropy change will be favorable, but we'll
have to scrape the food off the ground.  

Chem. major:   We could heat the can in a fire until the liquid in the can
goes to gaseous state, increasing the pressure inside the can until it is
strong enough to deform the can, eventually tearing the metallic bonds.
Unfortunately, if we're in the area, the shrapnel will kill us.

Economics major:  Assume a can opener...
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A man owns a horse race track.  It's pretty successful until one day a 
competitor builds another track across the street.  Since the other guy has
faster horses, he starts to lose all his business.  He figures, "If I can
figure out a way to get the horses running at my track to go faster, I can
steal the customers back and stay in business."

So he hires a biochemist, a civil engineer and a mathematician to help him
make his horses go faster.

The biochemist go away for two weeks to work on the problem.  When he 
returns he tells the owner "Well, I can give about a 5% increase in the 
speed of your horses, but it involves using these unapproved chemicals."

The owner tells him that he doesn't want to run an unethical racetrack, so
that idea is scrapped.

The civil engineer goes away for three weeks to work on the problem.  He 
returns to tell the owner, "By redesigning parts of the track itself, I 
can give you a 15% increase in the speed of the horses, but these changes
will cost about a million buck."  The owner decides that is far too expensive.

Finally the mathematician goes away to work on the problem.  After 6 weeks,
he returns to tell the owner, "Well, I've figured out a way to give you a
50% increase in the speed of your horses."

The owner replies, "That's fantastic! How?"

He replies "First we assume a spherical horse..."