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Path: utzoo!watmath!clyde!cbosgd!ihnp4!alberta!jim
From: jim@alberta.UUCP (Jim Easton)
Newsgroups: net.physics
Subject: re: HELP! Real life physics problem.
Message-ID: <725@alberta.UUCP>
Date: Thu, 14-Nov-85 15:34:22 EST
Article-I.D.: alberta.725
Posted: Thu Nov 14 15:34:22 1985
Date-Received: Sat, 16-Nov-85 01:00:55 EST
Distribution: net
Organization: U. of Alberta, Edmonton, AB
Lines: 44

> 	I have a small physics problem for all you net.physics.pudits out
> there. I have an assignment to drop a brick and an egg in a shoebox out
> of a two story window onto a sidewalk. The egg must not break (of course)

Having seen umpteen inappropriate responses to your question I finally
succumbed to answering.  Eg. the suggestion of placing the egg between
two bricks is silly - the top brick will crush the egg.

The idea is to protect the egg from point forces.  ie. If it's just
resting on a table the entire force holding it up is being applied
at one point (vis. where it's in contact with the table).

If its in water the forces applied to the body are applied over the egg's
entire surface and are proportional to the "depth".  Pressure gradients
due to acceleration are the same inside the egg as outside and the shell
should experience no net pressure differences.  This is assuming equal
densities and that compressibility can be neglected which is not, in fact,
the case (ie. there is a troublesome air bubble) but it's close.

The suggestion of filling the box with water was a good start.  I would
get an old tobacco tin, fill it with water and put the egg in that.  Eggs
sink - so it has point contact with the bottom of the tin - not a good
situation since a large force will be applied.  Therefore I would increase
the density of the water to the point where the egg would just barely float
(try adding salt)  Ideally the air bubble in the egg should be above the
surface of the water or the surface inside should be level with the surface
outside.

It's my guess that the above could be dropped directly and the egg wouldn't
break but one can improve the situation some more yet.  The idea now is to
decrease the force applied to the tobacco tin by spreading it over a longer
time.  You can do this by putting some padding (tightly crumpled newspapers
would probably do very nicely) under it.  The inertia of the tin will compress
the padding but more significantly spread the force over a longer time.

If it were me I would fill the box with crumpled newspaper, putting the tin
at one end, tie the lid on and drop it endwise (if you don't know which end
I have been wasting my time).

As for the brick I believe that it was meant to be used to compress some
padding, thus increasing the deceleration time, with the egg resting on top
of it.  In my suggestion the water in the tin supplies the required inertia.

	Jim Easton (..!alberta!jim)