The sight of an ordinary egg sinking in tap water is expected, but its ability to float on the water’s surface is a fascinating demonstration of physics. This simple kitchen experiment allows a seemingly dense object to defy gravity. The secret lies in salt, a common pantry item that alters the water’s physical properties. Understanding this phenomenon involves looking closely at the scientific principles that govern why things sink or float.
Understanding Density and Buoyancy
The physical concept that dictates whether an object sinks or floats is density, which measures an object’s mass relative to its volume. Plain tap water has a density of approximately one gram per milliliter (g/mL). Since an average raw egg is slightly denser than this (around 1.03 g/mL), it sinks when placed in a glass. For an object to float, its density must be less than the density of the surrounding fluid.
The upward force exerted by a fluid is known as buoyancy, which counteracts the egg’s weight. According to Archimedes’ principle, this buoyant force equals the weight of the fluid the object displaces. Adding salt introduces new mass without significantly changing the total volume of the liquid. These dissolved particles increase the water’s density. When the saltwater solution becomes denser than the egg, the buoyant force increases enough to push the egg upward and allow it to float.
The Specific Salt Measurement
Achieving the required density shift to make an egg float demands a large amount of salt. The exact ratio needed is variable, depending on the egg’s size and the volume of water used. A standard guideline involves dissolving a significant quantity of table salt into the water, often near the saturation point.
A practical guideline for a tall glass of water is to use approximately 6 to 8 tablespoons of salt, or about one-quarter to one-third of a cup of salt for every cup of water. This concentration is required to raise the water’s density above the egg’s average density of 1.03 g/mL, causing the egg to float. This is a much higher salt concentration than the world’s oceans, which have a salinity of around 35 grams of salt per liter of water.
Performing the Floating Egg Experiment
To replicate this experiment, you will need a raw egg, a clear container, water, table salt, and a spoon for stirring. Begin by filling the container halfway with water and gently placing the egg inside to confirm it sinks. Remove the egg and add the salt, stirring vigorously until the grains are fully dissolved.
After the salt is dissolved, carefully place the egg back into the solution to observe it floating near the surface. To demonstrate the density difference visually, slowly pour plain, unsalted water over the top of the salt solution. Because the fresh water is less dense, it floats on top of the salt water. The egg will then suspend mid-way between the two layers, resting on the denser saltwater below. Using warm water can help the salt dissolve more quickly.