Help with Calculating Uncertainties

In summary, the conversation discusses managing uncertainties in a physics lab where a ball's bounce height is measured using a motion sensor. The smallest value the sensor can measure is 0.0001, resulting in an uncertainty of ±0.00005. However, the measured values have only 4 decimal places, leading to a mismatch in decimal places when trying to express the uncertainty. The conversation suggests using multiple trials and accounting for both instrument error and repeatability error, which may be larger than the instrument's precision.
  • #1
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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  • #2
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.
 

FAQ: Help with Calculating Uncertainties

What is the purpose of calculating uncertainties?

The purpose of calculating uncertainties is to determine the level of confidence or reliability in a measurement or calculation. It allows scientists to understand the potential errors and limitations in their data and results.

How do I calculate uncertainties?

To calculate uncertainties, you need to determine the precision and accuracy of your measurements, and then use statistical methods to estimate the uncertainty. This can involve using standard deviation, error propagation, or other techniques depending on the type of measurement or calculation.

What factors can contribute to uncertainties?

Several factors can contribute to uncertainties, including limitations in measurement equipment, human error, and natural variations in the data. It is important to identify and minimize these factors as much as possible to reduce uncertainties.

Why is it important to report uncertainties?

Reporting uncertainties is important because it allows other scientists to understand the reliability of your data and results. It also promotes transparency and helps to identify potential sources of error in the research.

How can I reduce uncertainties in my calculations?

To reduce uncertainties in calculations, you can improve the precision and accuracy of your measurements, use more advanced statistical methods, and increase the sample size of your data. It is also helpful to consult with other experts in the field to ensure your methods are sound.

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