Requirements (Instruments, Chemicals & Other) :

• A glass cylinder of about 5 cm (or more) in diameter and about 100 cm in length
• Spherical metal balls of diameters ranging from 1 to 3 mm
• Stop watch
• Screw gauge
• Meter scale
• Experimental liquid (water)

Procedure :

1. Select three sets of balls; measure the diameter (2r) and hence the radius (r) of each ball by screw gauge. If the balls are very small, use a microscope for the measurement of the radius.
   
2. Set the cylinder vertically on a stand and pour the experimental liquid (water) slowly.
   
3. Measure the height H of the liquid column by a meter scale.
   
4. Put horizontal marks Y and Z on the outer surface of the cylinder.
   
5. Wet the balls thoroughly in the experimental liquid and then drop one ball from each set gently one by one starting from the largest size with the help of a spatula into the liquid in the cylinder so that they fall centrally.
   
6. For each ball, note the times of crossing of the distances Y and Z by a stop watch. Note the reading in Table.
   
7. After adjusting the positions of the markings Y and Z, drop the balls of one set gently again one by one and note by a stop watch the time taken by each ball in crossing the marks Y and Z. Measure the distance YZ by a meter scale and obtain the terminal velocity ( v' ) by dividing the distance by the mean time for a set of balls