Various motor oils with different viscosity ratings, e.g.:.For information on how internal combustion engines work, see:īrain, M., 2006.For a more advanced article on the physics of viscosity, see:.Viscosity, Wikipedia, The Free Encylcopedia. For more basic information on viscosity, including the viscosities for several different liquids, see:.Viscosity: Teacher Page, Hawaii Space Grant Consortium. This article describes a method for measuring viscosity of a liquid:.How To Read an Oil Can, Machinery Lubrication Magazine, May 2001. What do the SAE ratings on motor oil mean? Find out from this article:.Why is it important for motor oil to maintain its viscosity over a wide range of temperatures?. ![]() What do the SAE ratings on motor oil mean?.The Experimental Procedure section has more detailed instructions. You can use a water bath to heat or cool the oil to different temperatures in order to see how its viscosity changes with temperature. The amount of friction that the sphere experiences as it falls will be related to its surface area, which is proportional to the square of the sphere's radius. The density factor in the equation accounts for this. ![]() You would also expect a sphere that has higher density (i.e., is less buoyant) would fall faster than a sphere with lower density (i.e., is more buoyant). Conversely, if the sphere falls more slowly, the viscosity is greater. with greater velocity), v is greater and η, the viscosity, is smaller, as we would expect. So the equation tells you to take the density of the sphere minus the density of the fluid (Δ ρ), multiply this by 2 ga 2, and then divide the result by 9 v. The other variables in the equation are g, for the accleration due to gravity (980 cm/s 2), a for the radius of the sphere (in cm), and v for the average velocity of the sphere as it falls through the fluid (in cm/s). The capital Greek letter "delta" (Δ) is often used as shorthand for taking the difference of something. The variable commonly used to represent density is the Greek letter "rho" ( ρ). The variable commonly used to represent viscosity is the Greek letter "eta" ( η). It may look intimidating at first, because it has some Greek letters in it, but don't let that scare you. The equation (Equation 1) shows you how to calculate the viscosity from your measurements. In order to calculate the viscosity, you'll have to measure the time it takes the sphere to fall, the distance the sphere falls, and the density of the sphere and the fluid. You can make your comparisons using the measured time for the sphere to fall, or you can take your project a little further and actually calculate the viscosity. You will release a sphere (glass marble or steel ball bearing) at the surface of the liquid and time how long it takes for the sphere to fall to the bottom of the beaker or cylinder. Instead of using fancy glassware, you can use a Pyrex beaker or graduated cylinder. Ostwald-type viscometer for measuring viscosity of liquids. Because viscometers are expensive (more than $170), you'll use a slightly different technique for this experiment.įigure 1. To measure viscosity at different temperatures, the viscometer is placed in a water bath. ![]() The higher the viscosity, the longer it will take the fluid to drain through the tube. The suction is removed, and the time it takes for the fluid to drain out is measured. Fluid is drawn up from the cup on the lower left into the tube on the right, using a suction bulb. Viscosity of liquids can be measured with a special piece of glassware called a viscometer (see Figure 1). For an engine lubricant, it is important that the viscosity does not change significantly as the temperature increases. Cooking oil has a higher viscosity-it pours more slowly than water. Water is an example of a fluid with low viscosity-it pours easily and quickly. The viscosity of a fluid is a measure of the fluid's resistance to flow. One way of measuring an oil's ability to lubricate is to measure its viscosity. The oil must be able to keep the piston moving smoothly at cold temperatures (when the engine first starts up) and also at the normally high operating temperature of the cylinders.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |