# Atwood's Machine Lab Help (proportional error)

1. Sep 17, 2014

### atir.besho

I have attached the lab

right now I am stuck on proportional error in multiple variables

I wanna take the lab step by step so i can learn how to do calculate all the variables from now on.

I have lab partners during the lab but I am completely clueless when I am working on it on my own.

Can someone just explain the formula needed to get the proportional error please?
I know I need 1 gram as uncertainty.

#### Attached Files:

• ###### lab 2 pg 1.jpg
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2. Sep 17, 2014

### Simon Bridge

For independent measurements $x\pm\sigma_x$ and $y\pm\sigma_y$, the proportional errors are given by:$$p_x=\frac{\sigma_x}{x}, p_y=\frac{\sigma_y}{y}\\ z=xy\implies p^2_z=p_x^2+p_y^2$$