A small particle of radius 100 nm and density 1.05 g/cm (~density of polystyrene) falls under the action of gravity. You will need the Stokes equation for colloids (easy to find on the web or an introductory colloids book). a. If the viscosity of air is 1.8 x 10-5 Pa-s, what is the terminal velocity in mm/sec? b. What is the terminal velocity of a 50 nm radius particle of the same material in air? Note, this is about the diameter of a COVID virus particle. c. What is the terminal velocity of a 500 nm radius particle of the same material in water?