Scribbling on paper

Quote from a reader: “I've learned that if you ask a physicist a hypothetical question, they will most likely try to give you a real answer. As a result, never ask a physicist a hypothetical unless you're ready for a real explanation and potentially hand-drawn diagrams on napkins. I love you guys.”

A back of the envelope calculation is a rough estimate performed on a random scrap of paper (like the back of an envelope). They are synonymous with physicists. http://en.wikipedia.org/wiki/Back-of-the-envelope_calculation

Let's go through an example of one of these calculations:
Estimate the number of pizzas consumed by all the students at the Northwestern University during one quarter. (Adapted from University of Maryland)

Error Bars, Average Heights, and Pizza

Loyal reader, have you read your research article yet? Perhaps, you've noticed little lines on all the figures and wondered what they are. Those are error bars.

In the first post, I talked about the type of error that arises due to our finite measurements.This post is about another type of error called standard deviation, which basically relates to the spread of a data set.

You take the magic ruler from the first post and attempt to find the average height of Americans. Ignoring sample size, you take two small groups of five people randomly found on the street.

Group 1 Heights: 5’7”, 5’8”, 5’9”, 5’10”, and 5’11”

Group 2 Heights: 5’3”, 5’6”, 5’9”, 6’0”, and 6’3”