Eggshells are made of calcium carbonate, which dissolves in acid. A fun and easy way to teach children about this is to fill a jar with white vinegar and drop a hard-boiled egg into it. Observe the egg over a 72-hour period and watch the shell dissolve away. The acetic acid in the vinegar is reacting with the calcium carbonate in the shell. You can see the carbon dioxide bubbles this creates floating to the surface.
Inertia describes the force that resists the change in movement or direction of a substance. You can show this force by spinning a hard-boiled egg on a table and a raw egg on a table. The raw egg will move more slowly than the hard-boiled egg. This is because the inertia of the liquid in the raw egg slows down the movement.
Without their shells, eggs are held together by their membranes. This fact provides teachers with a good opportunity to talk about osmosis. Dissolve the shells of two eggs in white vinegar. Put one egg in a jar of water and the other in a jar of corn syrup. Leave for 24 hours and then observe what changes have been made. The egg membrane allows water to flow freely through it but blocks larger particles like the sugar in corn syrup. For this reason, the egg in the water should have remained intact. The egg in the corn syrup, however, should be deflated. The reason for this is that egg membrane is around 90 per cent water and corn syrup is around 25 per cent water, so the water in the egg membrane has moved outward into the corn syrup by the process of osmosis -- the movement of water from an area of more water to an area containing less water through a partially permeable membrane.
The shape of an object affects how much weight it can carry. This is a useful thing for humans to know when they are building structures which need to hold a large amount of weight without crumbling, like bridges. The strength of the dome shape, which can be seen in bridges, can be explained by showing the surprising strength of an egg. Take a wooden board and place one end of it on a pile of books on the floor. Place the other end on fewer books supporting an egg standing upright so that the narrower end of the egg is pointing at the ceiling. The egg needs to be standing upright, with the narrower part of its structure pointing at the ceiling. Ask the children to guess how many pounds the egg can take before it smashes. Then ask them to walk on the plank of wood to show how strong the egg really is. The reason the egg is strong is because its dome shape means weight is distributed down the curves and to the wider base.