Section 4.12 Warning on Unit Conversions and Ethics

Warning on Unit Conversions

Now that we have seen lots of unit conversion examples, I want to remind you that you can only convert units of the same dimension. So you can convert meters to feet or feet to centimeters because those are all units of Length. You can convert Newton to pound because those are both units of force. Anytime you are provided with information in one dimension and need an answer in a different dimension, you will need to have an equation that relates those dimensions in order to solve.

One example of this is kg to lb. Most people in the United States will give their weight in units of lb while those who use SI sytem will often give you theirs in units of kg. Remember that kg is a unit for the dimension of mass while lb is a unit for the dimension of force. The equation used to relate mass to for is \(F=m*a\text{.}\) Therefore, if you want to find out how many kgs are in 230 lbs, you will need to convert 230 lb to a mass and the convert to kg. Let’s see what this looks like.

\(F=ma\)

\(230\,lb=m*32.2\,\frac{ft}{s^2}\)

\(m=\frac{230\,lb}{32.2\frac{ft}{s^2}}=7.14\,\frac{s^2}{ft}=7.14\,slugs\)

Now that we have a mass, we can convert slug to kg.

\(7.14\,slugs*\frac{14.59\,kg}{1\,slug}=111\,kg\)

Ethics

Humans are fantastically complicated and intelligent (sometimes) creatures but we still make mistakes on the occasion. Sometimes the consequences are small (i.e. a typo in a textbook) or sometimes the consequences are huge (i.e. a plane crashes and hundreds of people die).

In engineering, making mistakes can have huge consequences. You can find examples of engineering mistakes killing people all over the place. For example, the Colombia space shuttle disaster resulted from a piece of foam that came off of a tank and cut through the wing. An engineer designed a crappy bridge at FIU and it collapsed killing people. The list goes on, and the point is, that when engineers make mistakes, disasters happen.

The ethics questions I would like you to consider for this chapter is: who is to blame and how should we punish them?