When you gently place a raw egg into a glass of ordinary tap water, it sinks straight to the bottom. The egg does not float because its density is greater than that of the water. If you now slowly add salt to the water and stir, something interesting begins to happen. As more salt dissolves, the egg starts to rise. Eventually, it may hover in the middle of the glass or float at the surface. The egg itself has not changed at all. What has changed is the density of the liquid around it.

Density describes how much matter is packed into a certain volume. When salt dissolves in water, more particles occupy the same space, increasing the water’s density. A denser liquid can push upward more strongly on objects placed inside it. This upward force is called buoyancy. Once the buoyant force becomes equal to or greater than the weight of the egg, the egg no longer sinks.

This experiment shows that floating and sinking are not only about weight, but about the relationship between the density of an object and the density of the surrounding fluid. If you want to see where this principle appears outside a glass and in the real world, come back next week.