Purpose

To illustrate the effect of viscosity upon rate of liquid flow.

Materials

4 Graduated cylinders,100-mL

SAE 10- and 40-weight motor oil (or alternate with low and high SAE numbers)

2 Beakers,1000-mL

Hot plate or burner

Ice

Safety and Disposal

Hot water may cause burns. Retrieve the motor oil to be stored and used again next year. Wash out the cylinders with detergent and dispose of the waste in the sink.

Procedure

1. Add 100 mL SAE 40-weight oil to two of the graduated cylinders.

2. Place one of these cylinders into a beaker containing hot water and the other into a beaker containing cold water. Allow them to stand for about five minutes. Perform Step 3 while waiting.

3. Add 100 mL SAE 10-weight oil to the third graduated cylinder and 100 mL SAE 40-weight oil to the fourth graduated cylinder.

4. Drop a plastic bead or glass bead into each cylinder one at a time. Record the time it takes for the bead to sink to the bottom in each cylinder.

5. Remove the first two graduated cylinders from their respective water baths. Predict the times needed for a bead to fall to the bottom of the cylinder. Drop the beads and measure the duration of the fall to the bottom.

Remarks

Ask students the following:

1. On a cold winter day in Fargo, ND, which motor oil would you want to use to start your car? [SAE 10 for easy low-temperature starting.]

2. During hot weather, which motor oil provides the most protection to your car? [SAE 40 for better load capacity in bearings at normal running temperature.]

3. Distinguish between density and viscosity? [Density is a property of matter representing mass per unit volume. Viscosity is the resistance of a liquid to flow.]

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