How can i find the uncertainty from a graph.....i searched on the internet and i had to draw error bars...what are error bars???
Error bars tell you how inaccurate your data point is. The larger the error bars, the less accurate the measurement.
Imagine you've got a ruler and were measuring the length of a box. Up close, you can measure it pretty accurately, giving you, say, 1.33 m +/- 0.01. Your error is very small because you had a good way to measure it. But if you had to stand across the room and try to estimate it from there, you might have to say 1.0 m +/- 0.5; or much larger error since you don't have good measuring technique.
Example : Let's say you gotta plot the point 5 +/- 0.5 m on a graph
So you plot the point 5 and the draw a line from 4.5 to 5.5 while passing through 5, so as to represent the errors. The line you just drew is called an error bar
Here is something which might help 
