Hydrostatic Pressure vs Osmotic Pressure
Pressure is defined as the force per unit area applied in a direction perpendicular to the object. Hydrostatic pressure is the pressure experienced by a point inside the fluid. Osmotic pressure is the pressure that is needed to stop the fluid transfer of a semi permeable membrane. These concepts play a vital role in fields such as hydrostatics, biology, plant sciences and many other fields. It is vital to have a clear understanding in these concepts in order to excel in such fields. In this article, we are going to discuss what osmotic pressure and hydrostatic pressure are, the definitions of these two, similarities between hydrostatic pressure and osmotic pressure and finally the difference between osmotic pressure and hydrostatic pressure.
What is Hydrostatic Pressure?
The pressure of a static fluid is equal to the weight of the fluid column above the point the pressure is measured. Therefore, the pressure of a static (non-flowing) fluid is dependent only on the density of the fluid, the gravitational acceleration, the atmospheric pressure and the height of the liquid above the point the pressure is measured. The pressure can also be defined as the force exerted by the collisions of particles. In this sense, the pressure can be calculated using the molecular kinetic theory of gasses and gas equation. The term “hydro” means water and the term “static” means non-changing. This means hydrostatic pressure is the pressure of the non-flowing water. However, this is also applicable to any fluid including gasses. Since the hydrostatic pressure is the weight of the fluid column above the measured point it can be formulated using P= hdg, where P is the hydrostatic pressure, h is the height of the surface of the fluid form the measured point, d is the density of the fluid, and g is the gravitational acceleration. The total pressure on the measured point is the unison of the hydrostatic pressure and the external pressure (i.e. atmospheric pressure) on the fluid surface.
What is Osmotic Pressure?
When two solutions having different solute concentrations are divided by a semi permeable membrane, the solvent at the low concentrated side tends to move to the high concentration side. Imagine a balloon made of the semi permeable membrane filled with high concentration solution submerged inside the low concentrated solvent. The solvent will transfer to the inside of the membrane. This will cause the pressure of the inside of the membrane to rise. This risen pressure is known as the osmotic pressure of the system. This is a vital mechanism in transferring water to the inside of the cells. Without this mechanism, even trees cannot survive. The inverse of osmotic pressure is known as water potential, which is the tendency of the solvent to stay in the solution. Higher the osmotic pressure, lower will be the water potential.
What is the difference between Hydrostatic Pressure and Osmotic Pressure?
• Hydrostatic pressure is observed in any fluid, which is not moving. Osmotic pressure is only present in specific systems where the solution and the solvent are separated by a semi permeable membrane.
• Osmotic pressure cannot occur only with a pure fluid. Two different concentrated solutions are required for osmotic pressure. Hydrostatic pressure can occur only with one fluid.