# Pre Lab, how to find uncertainty

1. Feb 20, 2013

### Habibrobert

Hello,

I have been stuck on this prelab all day.I have finished all the questions except for the last one, where it asks you to find the uncertainty (or standard deviation) of Fave. I have tried every resource and nothing has helped so far. Any help would be great!

Thanks

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2. Feb 20, 2013

### rude man

When you multiply or divide two numbers with fractional error f1 and f2 respectively, what is the resultant fractional error of the product or quotient? (Assuming normal error distributions).

3. Feb 20, 2013

### Habibrobert

Hello,

I'm really sorry but I don't understand what you mean?

4. Feb 20, 2013

### rude man

Like, (x +/-Δx) * (y +/-Δy) gives (xy +/- what)?

Annd division is just 1/multiplication so it follows the same rule.

5. Feb 21, 2013

### Basic_Physics

The uncertainty in Fave, ΔFave, divided by the value of Fave (what rude man calls the fractional error) is given by

ΔFave/ Fave = Δ(Δp)/Δp + Δ(Δt)/Δt

where Δ(Δp) is the uncertainty in the change of the momentum and Δ(Δt) is the uncertainty in the time interval - see the summary at the end of