Making an egg float in water is a simple kitchen experiment that demonstrates how a liquid’s properties influence whether an object floats or sinks. An egg typically sinks in plain tap water, but adding a common household ingredient can cause it to rise and suspend itself within the liquid.
Understanding Density and Buoyancy
The ability of an object to float or sink is governed by two fundamental concepts: density and buoyancy. Density is a measure of how much mass is contained within a given volume. Water has a specific density, and an egg’s density is slightly greater than plain water, causing it to sink. When salt dissolves in water, it adds mass to the same volume, increasing the water’s overall density.
Buoyancy refers to the upward force exerted by a fluid that opposes the weight of an immersed object. An object floats when the density of the fluid it displaces is greater than or equal to its own density. By increasing the water’s density with salt, the water can exert a greater buoyant force, which lifts the egg.
The Floating Egg Experiment
To observe this principle, you will need an uncooked egg, tap water, table salt, a clear glass, and a spoon. Fill the glass about two-thirds full with plain tap water. Gently place the egg into the water; it will sink to the bottom.
Remove the egg and start adding salt to the water, about one tablespoon at a time. After each addition, stir thoroughly until the salt completely dissolves. This gradual process ensures even distribution, steadily increasing the water’s density. Continue adding and dissolving salt, then reintroduce the egg to check its buoyancy. The egg will eventually float as the water becomes dense enough to support its weight. While the exact amount can vary, a common starting point is 2 to 3 tablespoons of salt per cup of water, or roughly 10 teaspoons for a typical glass.
Variables to Consider
Several factors influence the amount of salt needed. Water temperature plays a role in how quickly salt dissolves; warmer water allows salt to dissolve more readily and efficiently.
The freshness of the egg also affects its buoyancy. As eggs age, an internal air pocket enlarges due to moisture evaporation, slightly decreasing the egg’s density. This can make older eggs float in less saline solutions or even plain water. The type of salt used impacts the dissolution rate. Finer-grained salts, like table salt, dissolve faster than coarser varieties, such as kosher salt, because they have a larger surface area.