PHYS 1130 - Introduction to Meteorology

1.4 Units in Physics

PHYS 1130 - Introduction to Meteorology
Chapter 1. Earth and Its Atmosphere

Instruction

Steps to convert units:

  1. Find an equality
  2. Convert the given number
    • Multiply by the part of the equality with the desired unit
    • Divide by the part of the equality with the units you started with

Example: The distance from Ephraim, UT, to Denver, CO, is 780 km. How many miles is this, if you are told that 1 mile = 1.6 km, \(780~km \cdot \frac{1~mile}{1.6~km} = 780\cdot \frac{1~mile}{1.6} = 487.5~miles\)

Additional Resources

Review Questions

  1. The distance from Salt Lake City, UT, to Ephraim, UT, is 118 miles. What is this distance in km? (Do a quick search of “How many km in 1 mile?” to get your equivalent relationship.)
    • After solving on your own, check the
  2. A common unit for wind speed used in meteorology is the knot. (Learn here about what a knot is and where it comes from.)

A tropical storm becomes a hurricane when it reaches 64 knots. What is this speed in mph? (Do a search for how many mph are in 1 knot) * After solving on your own, check the

  1. We often discuss pressure in \(mb\) (millibars). However, airports report pressure in $$inHg$ (inches of mercury). If the airport reports a sea-level pressure of 28.76 inHg, how many millibars is this if 1013 mb = 29.92 inHg?
    • After solving on your own, check the
## Question 1.4.1 1. The distance from Salt Lake City, UT, to Ephraim, UT, is 118 miles. What is this distance in *km*? (Do a quick search of "How many km in 1 mile?" to get your equivalent relationship.) Looking up a relationship, we find that *1 mile = 1.609 km*. Using this relationship, $$118~\cancel{miles}\cdot\frac{1.609~km}{1.0~\cancel{mile}} = 118\cdot\frac{1.609~km}{1} = 189.862~km$$
## Question 1.4.2 2. A common unit for wind speed used in meteorology is the __knot__. ([Learn here about what a knot is and where it comes from.](https://oceanservice.noaa.gov/education/tutorial_currents/06measure2.html)) A tropical storm becomes a hurricane when it reaches *64 knots*. What is this speed in *mph*? (Do a search for how many mph are in 1 knot) Looking up a relationship between *mph* and knots, we find that $$1 knot = 1.15 mph$$. So, 1 knot is just faster than 1 mph. Using this relationship, $$64~knots\cdot\frac{1.15~mph}{1~knot} = 73.6~mph$$ So, a tropical storm becomes a hurricane at a speed of 73.6 mph.
## Question 1.4.3 3. We often discuss pressure in *mb* (millibars). However, airports report pressure in *inHg* (inches of mercury). If the airport reports a sea-level pressure of *28.76 inHg*, how many millibars is this? The relationship between *inHg* and *mb* is $$1013~mb = 29.92~inHg$$. Since we are starting with *inHg*, we'll put *mb* on top and *inHg* on bottom. $$28.76~inHg \cdot {1013~mb}{29.92~inHg} = 973.73 mb$$