by Bryan Uber

Created on: August 14, 2009   Last Updated: August 18, 2009

Why Objects Float?

The reason an object floats is due to the object's density in relation to the density of the liquid or gaseous material it is emerged. An example of an object floating is a hot air balloon. The hot air balloon floats because the air inside of the balloon is heated to create a difference in temperature. Since the air inside the balloon is at a higher temperature, this indicates that the molecules of air inside the balloon are traveling faster than the molecules of air outside the balloon. Since the air molecules are traveling faster, this equates to a less dense medium, thus the balloon experiences lift or float. In order to control the height in which the hot air balloon travels, the passenger can regulate the temperature of air inside the balloon by controlling the propane torch. Increasing the temperature of the air inside the hot air balloon will enable the balloon to reach a less dense medium of air. The earth's atmosphere has different levels of density. The densest air is around ground level, and the least dense air is in the upper atmosphere. Once the balloon reaches an atmosphere that is of the same density of the air inside the balloon, one can state that the system is equalized.

This example can be applied to liquid objects as well. If an object is placed into a liquid medium, then the term that is used to determine if the object can float is buoyancy. Buoyancy is a word that explains the relationship of the object's mass per volume or density to the density of the liquid medium. If the object's density is less than the density of the liquid medium, the object will float. If the object's density is greater than the density of the liquid medium the object will sink. You might find yourself asking, how can a ship float if its known that the ship weighs thousands of tons? A ship can still float because the mass of water that is displaced by the ship is equivalent to the mass of the ship.

Solids, liquids and gases have different characteristics that must be analyzed in order to determine if an object will float. The difference between salt water and fresh water is their density. If one was asked to have an object float on salt water and sink in fresh water, this objective is achievable because of the difference in density. However, this objective is only achievable if one understands density.

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