Can you balance an egg on end at noon on December 21?
This is an urban legend.
There is no special change in gravitation on December 21 (the winter solstice in the Northern Hemisphere, when the Earth is closest to the Sun). If an egg cannot be balanced at any other time, it will not be any more possible on December 21.
And, oddly enough, the original date suggested was the vernal equinox (March 21 in the Northern Hemisphere). Nothing special about balancing then either.
submerge the egg in cold water - a very fresh egg in water will lie on the bottom. One that is a week or so old will sit on the bottom but bob slightly. One that is three weeks or so old will balance on its small end, with the large end reaching for the sky. A bad egg will float, with the large end up.
There is a small air pocket in the large end of an egg. When the egg is fresh, the pocket is only about 1/8th of an inch deep and about as large around as a dime. As the egg ages, it loses both moisture and carbon dioxide so that the size of the air space increases, making the egg (among other things) more buoyant. So, if you submerge a very fresh egg in water, it will lie on the bottom. An egg that is a week or so old will lie on the bottom but bob slightly. An egg that is three weeks or so old will balance on its small end. And bad egg will float.
You cant. There is a small air space in the big end of the egg. Whenit is fresh, it is only about 2mm deep and as large around 10mm diameter. As the egg grows older, it loses both moisture and carbon dioxide and shrinksinside the shell. Thiscauses the size of the air spaceto get bigger. The size of the air space inside the egg determines the buoyancy of the egg. therefore if you put a very fresh egg in water, it will lie on the bottom.as it gets older it will tend to float more. An egg that is more than 3 weeks old will balance on its small end and a bad egg will float.