Fluids, which include both liquids and gases, exert forces on objects placed within them. Whether an object floats or sinks depends on the relationship between the object’s weight and the upward force exerted by the fluid. This upward force is called the buoyant force. Buoyancy is the ability of a fluid to exert an upward force on an object immersed in it. Pressure within a fluid also plays an important role, as it increases with depth.

One of the earliest scientists to study buoyancy was the Greek mathematician Archimedes. He discovered that the buoyant force acting on an object equals the weight of the fluid displaced by the object. This idea became known as Archimedes’ principle. If the buoyant force is equal to or greater than the object’s weight, the object floats. If the buoyant force is less than the object’s weight, the object sinks. For example, a boat floats because it displaces enough water to create a buoyant force equal to the boat’s weight.

Scientists also studied how pressure behaves in fluids. French scientist Blaise Pascal developed Pascal’s principle, which states that pressure applied to a confined fluid is transmitted equally and unchanged throughout the fluid. This principle can be observed when squeezing a tube of toothpaste. The pressure applied at one end moves through the toothpaste, forcing it out of the opening. Hydraulic lifts and car brakes also use Pascal’s principle to transfer pressure through fluids.

Another important discovery about fluids was made by the Swiss scientist Daniel Bernoulli. Bernoulli studied how moving fluids behave and found a relationship between fluid speed and pressure. Bernoulli’s principle states that as the velocity of a fluid increases, the pressure exerted by the fluid decreases. One example of this principle can be seen in airplane wings. Air moving more quickly over the curved top of the wing creates lower pressure above the wing than below it, helping produce lift.

British scientist Robert Boyle studied the behavior of gases and developed a relationship between pressure and volume known as Boyle’s law. Boyle’s law states that when the temperature remains constant, the pressure and volume of a gas are inversely related. This means that as the volume of a gas decreases, the pressure increases. Likewise, as the volume of a gas increases, the pressure decreases. For example, when air inside a syringe is compressed into a smaller space, the gas particles collide more often, causing the pressure to rise. In addition to the relationship between pressure and volume, gases are also affected by temperature.

The pressure-temperature relationship states that when the volume of a gas remains constant, an increase in temperature increases the pressure. This happens because warmer gas particles move faster and collide more frequently with the walls of their container, with greater force.  French scientist Jacques Charles also studied the behavior of gases and discovered a relationship between temperature and volume known as Charles’s law. Charles’s law states that when pressure remains constant, the volume of a gas increases as the temperature increases. Likewise, when the temperature decreases, the gas volume

Review:

1. What is buoyancy?
2. Explain Bernoulli’s principle.
3. Explain the pressure-temperature relationship.