Re: why do things float better in salt water rather than fresh water?

Telisa,
Why one thing floats on another has to do with the DENSITY of the two 
substances.  The substance with lower density will float on top of a 
substance of higher density.  The density of a substance means how much 
mass (or weight, so long as your still on planet Earth) it has per unit 
volume.  For instance, one gram of water takes up one milliliter of volume,
which means it's density is 1 gram/milliliter.  The density of a human body 
is fairly close to 1 gram/milliliter (abbreviated g/ml), but because 
there's so much air in the body, it's density is slightly less than 1 g/ml.  
Salt water is denser than plain water because the salt and the water 
molecules stick to each other more efficiently than they do to themselves.
(You can test this:  Try adding one cup of salt to two cups of water and 
then measure how much volume of salt water you get--it will be less than 
two cups.  This means that you have just increased the weight of the water
without increasing it's volume, which means it has a higher density!)So in
the case of your experiment, the density of the egg is greater than that of 
fresh water, but less than that of salt water.
As an aside, a couple years ago, I got to go to Israel and visit the Dead
Sea--named so because it is so salty (saline) almost nothing can grow in 
it. It is considered to be a SATURATED solution, meaning that if you added 
any more salt it would not be able to dissolve, but would remain in crystal 
form.  The water in the Dead Sea is so dense that it is difficult to avoid 
floating in it!  All you have to do is walk in, lean back a little, and 
your legs just lift up and you float!  It was pretty cool!  Maybe you 
should try and talk you teacher into a field trip!
I hope this answers your question.  Feel free to write me if there's 
anything that wasn't clear.
Julie Braaten