La última actualización de esta entrada fue hecha el 10 abril, 2024 por Hernán R. Gómez
What is the number and units of a magnitude?
In this article, we will talk about the importance of units. Surely, when you’re walking to a friend’s house, as you’re getting close, you send them a WhatsApp message indicating that you’re nearby. If they ask, “How far are you from my house?” how do you respond? Here are some options:
- I’m at 5. Don’t worry.
- I think I’m about 5 blocks away.
- I’m 5 km away, my GPS says.
One of the options might have sounded odd. And most likely, it was the first one. Yes. It seems like something is missing, doesn’t it? 5 what? 5 blocks? 5 kilometers? 5 meters? It doesn’t seem like the best option to respond to your friend if you don’t want them to reply with a “5 what?”
In physics, it’s crucial to provide detailed information about the different magnitudes you use daily.
For example, can you imagine a news report that says:
“Today in the city of Madrid, there will be winds of 20, a temperature of 32 in 4, and then there will be a 32% chance of small showers.”?
Did you understand anything the meteorologist was trying to express? Neither did we. That’s why they usually say, correctly:
“Today in the city of Madrid, there will be winds of 20 km/h, a temperature of 32°C in 4 hours, and then there will be a 32% chance of small showers.”?
Much clearer, isn’t it? The thing is, it’s really important to mention the unit of each magnitude, along with the number. It’s not the same to say you’re 50 meters from your friend’s house as it is to say you’re 50 kilometers away. If you were 50 meters away, they should already be ready to open the door. If you’re 50 kilometers away, they’ll have enough time to prepare a snack for when you arrive.
In other words, every magnitude must have both the number and the unit written correctly:
| Magnitude | Unit of Measurement | Measurement Instrument |
| Length | Meter (m), centimeter (cm), feet (ft), inches (in) | Ruler, Tape Measure, Caliper |
| Width | Meter (m), centimeter (cm), feet (ft), inches (in) | Ruler, Tape Measure, Caliper |
| Height | Meter (m), centimeter (cm), feet (ft), inches (in) | Ruler, Tape Measure, Caliper |
| Volume | Cubic meter (m³), litre (L), fluid ounce (fl oz) | Measuring Cup, Graduated Cylinder, Volumetric Flask |
| Weight | Newton (N), kilogram-force (kgf) | Scale, Balance |
| Mass | Kilogram (kg), gram (g) | Scale, Balance |
| Temperature | Celsius (°C), Fahrenheit (°F), Kelvin (K) | Thermometer |
In the information provided by the news report: “Today in the city of Madrid, there will be winds of 20 km/h, a temperature of 32°C in 4 hours, and then there will be a 32% chance of small showers.”, the winds are blowing at a speed of “20 km/h”, where 20 is the number and km/h is the unit. Likewise, the temperature was “32 °C”, where 32 is the number and °C is the unit. And the most striking case was that of “4 hours”: without the unit (hours), we wouldn’t even know what the weatherman was talking about. “In 4 what?”, you might have wondered.
On the other hand, it’s important to know which unit to use in each situation, as incorrect units should NEVER be used. For example, you can’t measure temperature in kilometers, as it makes no physical sense. Temperature is measured in, for example, °C (degrees Celsius or centigrade), K (kelvin), or °F (degrees Fahrenheit). We recommend clicking here to learn all possible units for each magnitude.
Fun facts
Image of the current Air Canada aircraft. Don’t forget the importance of units! Current aircraft of Air Canada. Don’t forget the importance of units! Once, in 1983, a flight of Air Canada ran out of fuel while flying over the town of Gimli, located in the Canadian province of Manitoba, which has about 2000 inhabitants. Since the fuel gauge wasn’t working, the crew used a tube to measure how much fuel they had previously loaded. However, there was a problem they hadn’t considered.
In 1970, Canada had switched to the metric system, and this aircraft was the first of the company to use the new measures legally established. They converted volume measurements into mass measurements (Big mistake!); they confused pounds of fuel with kilograms. In other words, they had the correct number but the wrong unit. The aircraft had about half the fuel they believed and it could have been a tragedy if not for the pilot, who made an emergency landing on a street in the small town. What a scare, all because of something as simple as units!
A must watch
We recommend the following video in Spanish!
If you want you can read this article in Spanish by clicking here.
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