This is a suggestion described in the pdf file below how to use a pendulum along with a motion detector to determine the gravitational constant g.  The results are more exact than to use only a stopwatch and at the same time one is able to read more than a time period. 
The precision of the constant goes to 4th decimal place, at least, as well one sees the friction force as a change of speed of sphere.
The details are in the article below.

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