Watching an object fall, along a ruler, using a stopwatch to take the time from when the object flies passed the upper part of the ruler, and again when it hits the floor (bottom of the ruler)
The Attempt at a Solution
My friend is doing introductory mechanics and says that since using a stopwatch requires someone to react to something visually, there'll have to be an uncertainty of about 0.2 seconds, both at the beginning and at the end, for a total of 0.4 seconds. From my experience this is correct, hence why they shouldn't have done it this way, as the fall takes about 1 sec, so the fractional error is enormous. But I'd be happy to have it confirmed before I agree with him. Is this correct?
(People in his group argue for 0.05 seconds in total, which given how they performed the experiment, sounds unreasonable to me)