Fahrenheit temperatures are not always bigger than celcius

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

28 March 2021

Which of these numbers is greater: -40 or -50? (Don’t ignore the negative sign.) The answer is -40. Even though 50 is bigger than 40, when these values are placed on a number line and we read them from left to right, we come across -50 before -40; hence -50 is less than -40.

Now, the Pfizer covid-19 vaccine requires storage at a temperature of -70 degrees celcius which is equal to -94 on the fahrenheit scale. Which of these numbers is greater? It is -70, of course. But that seems strange because we are normally used to the fahrenheit values being bigger than the celcius ones.

For example, the boiling point of water is 100 degrees celcius or 212 degrees fahrenheit. Also, the average of human body temperature is 36.6 on the celcius scale which translates to 98.6 on the fahrenheit.

And so on, and so forth; for a given temperature, the degrees-F are usually bigger numbers than the degrees-C. But this does not hold true for all temperatures. We can understand why when we look at the scales more closely.

The range of degrees between freezing and boiling of water in the celcius scale is 100 (that is, from 0 to 100) while on the fahrenheit scale it is 180 (from 32 to 212). Therefore, as the temperature changes, the fahrenheit numbers change more quickly than the celcius ones.

Consider this: on the celcius scale, the human body temperature is 36.6 degrees above the freezing point (36.6 – 0 = 36.6). On the fahrenheit scale, however, the same temperature range (from freezing point of water to human body) has 66.6 degrees (98.6 – 32 = 66.6).

If we go in the reverse direction, we find the same trend. Zero degrees fahrenheit is equivalent to about -18 degrees celcius. We have traversed over 32 numbers on fahrenheit and only 18 on the celcius to reach the same temperature. Consequently, when we say that the temperature is so many degrees below freezing, we must clarify the scale we are referring to.

Obviously then, there is a point at which the fahrenheit numbers “overtake” the celcius ones. That is, where both scales have exactly the same number of degrees for the same temperature.

This happens at -40: -40 degrees celcius is the same temperature as -40 degrees fahrenheit. From this point downwards (to colder temperatures) the fahrenheit number is lower that the celcius one.