Help with Calculating Uncertainties

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SUMMARY

The discussion focuses on calculating uncertainties in experimental physics, specifically when measuring the height of a ball's first bounce using a motion sensor. The sensor's precision is ±0.00005, but the measured value of 0.6798 has only four decimal places, creating a mismatch in decimal places between the measurement and its uncertainty. Participants suggest that the uncertainty should reflect both instrument precision and repeatability, emphasizing that repeatability errors may significantly exceed the instrument's precision, potentially around ±0.03.

PREREQUISITES
  • Understanding of measurement precision and uncertainty in experimental physics
  • Familiarity with using motion sensors for data collection
  • Knowledge of significant figures and decimal place rules in scientific reporting
  • Basic principles of repeatability and reproducibility in experiments
NEXT STEPS
  • Learn how to calculate combined uncertainties in measurements
  • Explore the concept of significant figures in scientific notation
  • Investigate methods for reporting uncertainties in scientific tables
  • Study the principles of repeatability and how to conduct multiple trials effectively
USEFUL FOR

Students in physics labs, educators teaching measurement techniques, and researchers involved in experimental data analysis will benefit from this discussion.

conspicuous
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Homework Statement



I did a Physics lab in which I measured the height of the first bounce of a ball. I used a motion sensor to calculate it, so the uncertainty was really small: the smallest value it could measure was 0.0001, so the uncertainty would be 0.0001/2 = ±0.00005 (<--that's 5 decimal places). However, the values I got are, for example, 0.6798 (<--- that's 4 decimal places).

Homework Equations



In order to get a good mark in the 'data collection & processing' criteria, the values cannot have less or more d.p than the uncertainties. So how do I manage those uncertainties? For example, I can't write down '0.6798 ± 0.00005' because the decimal places don't match.

The Attempt at a Solution



I thought maybe about using scientific notation, but in a table it would look weird. For example, 0.6798 ± 5.0000 x 10^-4, because it still needs the same amount of decimal places.

Any help is very much appreciated. Thank you in advance!
 
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conspicuous said:

Homework Statement



I did a Physics lab in which I measured the height of the first bounce of a ball. I used a motion sensor to calculate it, so the uncertainty was really small: the smallest value it could measure was 0.0001, so the uncertainty would be 0.0001/2 = ±0.00005 (<--that's 5 decimal places). However, the values I got are, for example, 0.6798 (<--- that's 4 decimal places).

Homework Equations



In order to get a good mark in the 'data collection & processing' criteria, the values cannot have less or more d.p than the uncertainties. So how do I manage those uncertainties? For example, I can't write down '0.6798 ± 0.00005' because the decimal places don't match.

The Attempt at a Solution



I thought maybe about using scientific notation, but in a table it would look weird. For example, 0.6798 ± 5.0000 x 10^-4, because it still needs the same amount of decimal places.

Any help is very much appreciated. Thank you in advance!

While not actually solving the problem you see ...
I presume that you bounced the ball more than once - did more than one trial.

The uncertainty in a measured result usually include an instrument error [to what precision does the instrument work] plus a "reapeatability" uncertainty - how much variation did you get when you measured the same event several times.
Indeed, you may choose to repeat the experiment 10 times, then "ignore" the outliers as perhaps influenced the falling ball on release unexpectedly.
I would expect your repeatability error to be far larger than the precision of the instrument you were using.

While the instrument may measure to ±0.0005, the repeatability error may be as bad as ±0.03.
 

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