## Units and Order of Magnitude Calculations

• We will use the MKS system of units, which depends on
• meters to measure length
• kilograms to measure mass
• seconds to measure time
• You should be able to work with angles in both degrees and radians
• The following metric prefixes are vital:
```     giga       G         10^9
mega       M         10^6
kilo       k         10^3

centi      c         10^(-2)      only for centimeters, really
milli      m         10^(-3)
micro      mu        10^(-6)      (that's the Greek letter "mu")
nano       n         10^(-9)
```
• In some situations, you may not find the exact information you need to solve a problem; being able to take reasonable estimates and use them to calculate the order of magnitude of the answer can be very useful.
• The famous physicist Enrico Fermi was fond of setting, and then solving, puzzles which involve a good deal of common sense and order-of-magnitude calculation. I'm fond of them, too. Hint, hint.

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