Falling Speeds: Repeat the Measurement

Read repeated fall times and notice measurement limits.

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Learn the skill

Keep the object, release height, method and conditions alike. Add times and divide by the number of trials to find the mean. The range is the largest minus the smallest time. Repetition does not remove every systematic error.

Worked example

The practice times are 0.42, 0.38 and 0.40 s. Their total is 1.20 s, mean is 0.40 s and range is 0.04 s. All are invented observations.

Three invented elapsed times for the same short fall are 0.42, 0.38 and 0.40 seconds. Their mean is 0.40 seconds and their range is 0.04 seconds.

Would you believe it?

A timer showing extra decimal places does not guarantee an accurate result. Starting late or using the wrong distance scale can affect every repeated measurement.

NIST: measurement uncertainty

Question 1 What is the mean of the three times? 1.20 s 0.04 s 0.40 s

Question 2 What is the range? 0.80 s 0.04 s 0.40 s

Question 3 Which trial took the least time? Trial 2 Trial 1 Trial 3

Question 4 Why repeat a short-fall measurement? To guarantee all errors disappear To change the release height each time To see how much measurements vary

Question 5 A timer always starts late. Does repeating alone fix that? Only if times are averaged upward No, a consistent timing error can remain Yes, three trials fix every error

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