Some oils have a more stable viscosity, while others react to heat or cold if your oil's viscosity index is low, it may become thinner as it heats, which can cause problems as you operate your car on a hot summer's day. In addition, viscosity also affects the rate of oil consumption and the ease with which your vehicle will start in hot or cold conditions. That's because viscosity affects friction, and friction, in turn, affects heat. When you put oil into your car or truck, you should be aware of its viscosity. This is because the viscous drag in air opposes the velocity of raindrops as they descend due to gravity. If this does not occur, a person walking in the rain will be injured. Raindrops do not reach extremely high speeds during their free fall. Thus, the medium is homogeneous and continuous for such a body.Īpplications of Stoke’s Law Velocity of Raindrops The size of the body is small, but it is larger than the distance between the molecules of the liquid.The motion of the body does not give rise to turbulent motion. There is no slip between the body and the fluid.The body is perfectly rigid and smooth.The fluid through which the body moves must have an infinite extension.This results in a significant difference between the real rate of sedimentation and the rate measured using Stokes’ equation.Ĭonditions under which Stoke’s Law is valid are, Sedimentation is mitigated to some degree by Brownian migration. Brownian MovementĪnother aspect that can affect the precision of Stokes’ equation results is Brownian movement, which is a spontaneous (zigzag) movement of particles floating in a fluid caused by collisions with fast-moving atoms or molecules in the gas or liquid. These considerations are critical for using non-aqueous vehicles such as sesame oil, corn oil, and chlorofluorocarbon propellant (in aerosol suspension). The assumption is that if an automobile has a low dielectric constant, the double layer is several times thicker than in an aqueous medium, resulting in different zeta potential and, therefore, a different setting. As a result, the zeta potential is affected by the medium’s dielectric constant. The electrical potential between two charges is inversely proportional to the medium’s dielectric constant. The dielectric constant, which is not used in Stokes’ equation, is a significant parameter in many contexts. The equation contains only the viscosity of the medium. High solid content imparts additional viscosity to the system, which must be taken into consideration if the correct rate of settling is to be determined. When the solid content of a suspension is high, Stokes’ equation may not show the real sedimentation rate. This results in floatation or creaming most commonly seen in emulsion systems. Stokes’ equation is invalid if the density difference in the equation is negative that is when the particles are lighter than the dispersion medium. Various limitations of Stoke’s Law are discussed below in the article, Negative Density Difference in Stoke’s Equation Hence, this is the required relation of Stoke’s Law. Thus, the viscous force on a spherical body falling through a liquid is given by the equation,
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