You are Here: Home >< Physics

# Physics Experiment- Percentage Uncertainty?? watch

1. Hi im trying to work out the percentage uncertainty from results from a coursework experiment we did this week and i tried looking on the internet but i dont understand how to work it out. ?! Please help!!

Basically im trying the work out the percentage uncertainty from a 100g weight which i weighed twice and which i got 97.4g and 98.5g.
I know its the difference between them butthen im not sure whether to take away the average of the 2 results or 100g, and then x100% ?

Thanks.
2. (Original post by clarra)
Hi im trying to work out the percentage uncertainty from results from a coursework experiment we did this week and i tried looking on the internet but i dont understand how to work it out. ?! Please help!!

Basically im trying the work out the percentage uncertainty from a 100g weight which i weighed twice and which i got 97.4g and 98.5g.
I know its the difference between them butthen im not sure whether to take away the average of the 2 results or 100g, and then x100% ?

Thanks.
There are several ways of dealing with errors in this case.

But first thing - why do you say it's a 100g weight if you've measured its mass and obtained more or less 98.0g? I would say it doesn't matter whether you predict the mass of the weight to be 100g - just stick to your measurements. There would be one exception - if you are sure that the mean measured value should agree with the expected 100g within the uncertainty range, it might be worth considering if your measurement has been free from systematic errors.

As for the error, I would suggest to choose the way of average absolute deviation.

Absolute deviation of each result is the difference between the result and the mean of all results. Because you want all of them to be positive (to make it possible to add each other without their cancelling out each other), you take absolute value of each term. That is

.

The error in your measurement would be the average of all deviations, i.e.

,

in this case

.

Percentage error is the absolute error over the mean value (forget about the 100g!): .
3. thank you so muchh!!
was so stuck

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 12, 2011
Today on TSR

Do you?

### University open days

• University of Lincoln
Mini Open Day at the Brayford Campus Undergraduate
Wed, 19 Dec '18
• University of East Anglia
Fri, 4 Jan '19
• Bournemouth University