PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the viscosity of a sample oil through data analysis.

INTRODUCTION:
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its "thickness". Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a lower viscosity, while vegetable oil is "thick" having a higher viscosity. One method of determining viscosity is to time a ball falling through a liquid in question. The amount of time it takes is directly related to the viscosity of the liquid. Other data must also be considered such as density difference between the ball and the fluid, radius of the ball and temperature The equation for viscosity is:

viscosity = 2(delta p)gr² / 9v

where delta p is the difference in density between the ball and liquid, g is gravity, r is radius of the ball and v is the velocity of the ball falling through the liquid. If cm/g/s are used for all data the viscosity will have the units poise (g/cm s). Pa s would result for viscosity if kg/m/s were used as the data. Temperature has a huge effect on viscosity but in this lab temperature is held constant and is not considered.

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To calculate the velocity of an object falling through a column of liquid, the above meter is used. 2 photogates measure the time it takes the object to fall through a distance of 10 cm.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

2) Wear your goggles. Place the metal ball on the balance and record its mass. On the table is a small 10 cm ruler. Place the ball behind this ruler and a close-up view will appear allowing you to record its radius (one half the diameter).

3) Place the small beaker on the scale and note its mass. Grab the autopipette hanging from its rack and hold the tip in the sample oil in the large beaker. While holding it there, press 'p' to draw up 10 mL of oil. Autopipettes are used to collect a precise volume of liquid. Hold the pipette over the small beakers mouth and press 'p'. 10 mL (10 cm³) will be added to the beaker and the scale will display the combined mass of the beaker and oil. Subtract to find the mass of the oil and record the density of the sample oil from these two pieces of data.

4) Pick up the large beaker holding the sample liquid and position the left hand lip of the beaker centered over the mouth of the velocity tube. While holding the beaker above the tube press 'p' to pour. When the sample oil fills the tube to the etched red line, stop pouring. The velocity tube is used to hold a sample of oil to be tested. Two photogates are positioned 10 cm apart on the tube and will time the fall of a ball through this sample. The velocity is displayed on a meter in cm/s.

5) Turn on the velocity meter by clicking on the front red button. You are now ready to determine the velocity of the ball falling through the liquid. Pick up the ball and drop it into the mouth of the tube. Record the velocity of the falling ball. The ball has now been coated with the sample and the entire velocity tube must be cleaned so if you wish to try another run, press reset.

6) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.