For this essay I’ve decided to fulfill a promise I made to myself and write a compendium of mini essays on loosely related topics-all at least, science related with some math thrown in. Since much of my country is in the throes of writer storms, I have decided to focus first on the miserable wind chill factor, its limitations, and how to read a wind chill chart.
Basically, animal skin reacts to the wind’s drying affect. Think back to the last time you stepped out of a pool, lake, or shower and felt cool until you dried off. Why did you feel cool? We always have evaporation from the skin’s pours taking place and as it does, heat escapes into the atmosphere. The colder the air and the stronger the wind, the colder we feel. A blowing fan produces the same effect. Now, the question becomes “does a blowing fan cool a room down?” The short answer to the question is NO! Heat from the electric motor can actually increase the room temperature ever so slightly. Now, for the question, “Are inanimate objects affected by the wind?” With some environmental exceptions, the general answer is again No.
You read a wind chill chart just like a road mileage chart, . For example, if the temperature is 5 and the wind speed is 20 mph, then the wind chill is -15.
By Tom Skilling
- Chicago Tribune
- A good approximation of the wind-chill temperature can be found by multiplying the wind speed by 0.7 and then subtracting that value from the air temperature. For example, if the air temperature is 20 degrees and the wind speed is 25 mph, use the formula 20 – (25 x 0.7) to determine that the wind-chill temperature is 2.5 degrees.
- The actual wind-chill temperature calculated from National Weather Service tables is 3 degrees. The wind-chill temperature assumes a human face at a height of 5 feet above the ground on a clear night.
- Wind speed magnifies the effect of cold temperatures. Cold air blown by wind increases the rate of convective heat loss from human skin much more rapidly than calm air. Bright sun increases the wind-chill temperature by 10 to 18 degrees.(Skilling, T.)
- QUIZ 1 (answers after reference)
1. If the temperature is -15 and the wind speed is 35 mph, how long will it take for frostbite to occur?
2. What is the wind chill factor in question 1?
3.At what temperature & wind speed will the chill factor be -4?
For those of you in the Southern Hemisphere who are enjoying summer, I have included a discussion of the heat index.
| What is the heat index? |
| “It’s not the heat, it’s the humidity”. That’s a partly valid phrase you may have heard in the summer, but it’s actually both. The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. This has important considerations for the human body’s comfort. When the body gets too hot, it begins to perspire or sweat to cool itself off. If the perspiration is not able to evaporate, the body cannot regulate its temperature. Evaporation is a cooling process. When perspiration is evaporated off the body, it effectively reduces the body’s temperature. When the atmospheric moisture content (i.e., relative humidity) is high, the rate of evaporation from the body decreases. In other words, the human body feels warmer in humid conditions. The opposite is true when the relative humidity decreases because the rate of perspiration increases. The body actually feels cooler in arid conditions. There is direct relationship between the air temperature and relative humidity and the heat index, meaning as the air temperature and relative humidity increase (decrease), the heat index increases (decreases). |
| It surprises many people to learn that the heat index values in the chart above are for shady locations. If you are exposed to direct sunlight, the heat index value can be increased by up to 15°F. Heat indices meeting or exceeding 103°F can lead to dangerous heat disorders with prolonged exposure and/or physical activity in the heat. |
Classification Heat Index Effect on the body
Extreme Danger 125°F or higher Heat stroke highly likely
Danger 103°F – 124°F Heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity
Extreme Caution 90°F – 103°F Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity
Caution 80°F – 90°F Fatigue possible with prolonged exposure and/or physical activity
Quiz 2
1.What is the heat index with a temperature of 85 °F and relative humidity of 85 %
2. What is the level of concern at 86 °F & 60% humidity?
Converting from Fahrenheit to Celsius
0 degrees Fahrenheit is equal to -17.8 degrees Celsius:
0 °F = -17.8 °C
The temperature T in degrees Celsius (°C) is equal to the temperature T in degrees Fahrenheit (°F) minus 32, times 5/9:
T(°C) = (T(°F) – 32) × 5/9
or
T(°C) = (T(°F) – 32) / (9/5)
or
T(°C) = (T(°F) – 32) / 1.8 (Easier, I think)
Sample: Convert 68 degrees Fahrenheit to degrees Celsius:
T(°C) = (68°F – 32)/1.8 = 20°C
Some important conversions
| 32 °F | 0 ° C | freezing/melting point of water |
| 70 °F | 22 °C | room temperature |
98.6 °F 37 °C normal body temperature
212 °F 100 °C boiling point of wate
| · How to convert Celsius to Fahrenheit 0 degrees Celsius is equal to 32 degrees Fahrenheit: ( 0 °C = 32 °F) The temperature T in degrees Fahrenheit (°F) is equal to the temperature T in degrees Celsius (°C) times 1.8 plus 32: T(°F) = T(°C) × 1.8 + 32 or T(°F) = T(°C) × 1.8 + 32 Example Convert 20 degrees Celsius to degrees Fahrenheit: T(°F) = 20°C × 1.8 + 32 = 68 °F |
Stay tuned for the next installment.
| References The National Weather Service Silver Spring, MD |
Quiz 1
- 10 minute
2. -48 degrees
3. 10 degree, 10 mph
Quiz 2
- 102 dgrees
2 Extreme caution