Why Does an Egg Float When I Add Salt To the Water?

Understanding Density

• Density is a measurement of mass in a given volume; you can calculate density mathematically dividing an object's mass by its volume. The higher an object's density, the more mass it has for a given volume. Conversely, the lower an object's density, the less mass it has for a given volume. For instance, cork has a much lower density than lead. This means that, for an equal volume of each, the lead has much more mass than the cork.

Understanding Buoyancy

• Archimedes' principle states that the buoyant force acting on an object in a fluid is equal to the weight of the fluid displaced. Thus, an object displacing 5 lbs. of water will have a force of lbs. acting on it upward. If the object weighs less than 5 lbs., it will float. If it weighs more than 5 lbs., the buoyant force will not be enough to support it, and it will sink.

Weight and Mass

• Weight is directly proportional to mass, meaning an object that weighs more will have more mass. Therefore, "weight" and "mass" are interchangeable in terms of Archimedes' principle. If the mass of water displaced by an object is greater than the mass of the object, the object will float. This principle is important because it enables us to determine buoyancy by comparing the density of an object with the density of a fluid.

An Egg In Water

• The average density of a bird egg is 1.87 oz. per cubic inch. The density of water is 1 oz. per cubic inch. Based on Archimedes' principle, an egg placed in water will sink because it has a higher density than water. Stated differently, the buoyant force acting on the egg will not be great enough to support the weight of the egg.

An Egg In Salt Water

• Adding salt, with a density of 3.74 oz. per cubic inch, to water increases the water's density because it adds mass. While the addition of the salt will increase the volume of the water, the change in volume is miniscule compared with the increase in mass; for example, the salt water of the Dead Sea has a density of 2.15 oz. per cubic inch. Therefore, an egg will float in salt water. The density of an average egg, 1.87 oz. per cubic inch, is less than the density of the salt water, 2.15 oz. per cubic inch.