It is found experimentally that for any given liquid, provided that laminar or streamline flow exists, the stress exerted on the liquid is directly proportional to the velocity gradient that it causes in it. When a body moves with constant velocity through a fluid, it experiences a frictional drag force which opposes its motion. For a sphere of radius r when moving with velocity v in a fluid of viscosity h , this frictional force is equal to 6 p h rv. Since the sphere is moving at constant velocity, the forces acting on it are in equilibrium. A force diagram is shown below.
Procedure Weigh the graduated cylinder empty.
Fill it to the 100 mL mark with oil and reweigh. Add some more oil until the oil level is about 1 cm above the 100 mL graduation mark. Make three determinations or the diameter of one of the small spheres using the micrometer. Measure the room temperature and record it in the table. Determine an average value for the coefficient of viscosity of oil at room temperature.