Module 9: Fluids

Density is the mass per unit volume and is measured in kg/m3 or kg/L. Specific gravity is the density of the material divided by the density of water. Specific gravity has no units. Pascal’s principle states that the pressure applied to a fluid is transmitted throughout the fluid and to the walls of the container.

The Pressure-Fluid-Height relationship is used to calculate the pressure in a fluid. The pressure felt under water is determined by the pressure acting on the surface of the water and the depth of the water. 

Buoyancy is an upward force on a submerged object created by pressure differences in a liquid. Archimedes Principle states that the size of the buoyant force is equal to the weight of fluid that the object pushes out of the way. Whether objects float or not depends on how the density of the object compares to the density of the fluid. If the object’s specific gravity is less than or equal to one, the object floats in water. If the object’s specific gravity is greater than one, the object sinks in water. 

For moving fluids, energy conservation is used to determine changes in pressure while speed changes are controlled by the area of the pipe. Bernoulli’s Principle states that the pressure is lower in faster moving fluids. This pressure difference creates effects such as lift and curve balls.