When an orange is placed in water, it floats. However, if that same orange is peeled, it sinks immediately. The difference in behavior between a peeled and unpeeled orange in water can be explained by understanding how objects interact with fluids.
Understanding Buoyancy and Density
Whether an object floats or sinks in a fluid depends on two fundamental concepts: buoyancy and density. Buoyancy is the upward force exerted by a fluid that opposes the weight of an immersed object.
Density describes how much matter is packed into a given volume. It is calculated as an object’s mass divided by its volume. For an object to float, its overall density must be less than the density of the fluid it is in. Conversely, if an object’s density is greater than the fluid’s density, it will sink. Water has a density of approximately 1 gram per cubic centimeter (1 g/cm³).
The Unpeeled Orange: Nature’s Life Vest
An unpeeled orange floats due to its rind. The orange peel is highly porous and filled with numerous tiny air pockets. These trapped air pockets significantly reduce the overall density of the entire orange.
The air acts like a built-in flotation device, similar to a life vest. The presence of this air makes the unpeeled orange less dense than water, allowing it to remain afloat on the surface.
Even though an unpeeled orange is heavier than a peeled one, the volume occupied by the air in the peel is sufficient to lower its average density below that of water. This demonstrates that an object’s ability to float is not solely determined by its weight, but by its density relative to the surrounding fluid.
The Peeled Orange: A Denser Reality
When the orange peel is removed, the situation changes. The air pockets that contributed to the unpeeled orange’s buoyancy are no longer present. The remaining fruit, which is primarily composed of water and sugars, is denser than water.
Without the “life vest” provided by the air-filled peel, the overall density of the peeled orange becomes greater than water’s density. This increase in density causes the peeled orange to sink. This illustrates how altering an object’s volume and trapped air impacts its density and behavior in water.