float egg
Place an egg in a glass of water and it will sink.
Dissolve about 3 tablespoons of salt in the water and the egg
will float.
Put the egg into a glass which is about 1/3 full
of plain water. It again sinks to the bottom. Add the salt
water to the glass by pouring it gently down the side of the
glass into the water. Keep pouring until the glass is about
2/3 full. As you pour, the egg will rise and remain suspended
at the middle of the liquid.
The salt water goes to the bottom of the glass and the plain
water stays on top. The egg stays at the middle since it floats
on salt water and sinks in plain water.
Any object in a liquid is pulled down by gravity and pushed up
by the liquid. Light materials such as wood are pushed up more
than they are pulled down, so they float. Dense materials such
as rock are pulled down more than pushed up, so they sink.
[Dense materials have a lot of weight in a small space.]
It so happens that a material denser than the liquid sinks.
A material less dense than the liquid floats in that liquid.
The egg sinks because it is denser than plain water. The egg
floats in saltwater because it is less dense than saltwater.