3. You are an ecologist studying bottom-dwelling stream invertebrates. You need to measure the speed at which the water is flowing at a particular point you have chosen to study. You have a stopwatch, a long measuring tape, a supply of Ping-Pong balls (which float and are easy to see), and brightly colored flags that can be used to mark points along the shore or in the water. How would you use this equipment to estimate the instantaneous speed of the water