Metric system: units of distance (video) | Khan Academy (2024)

Video transcript

The base unit for distance inthe metric system is the meter. And to get a sense of how longa meter is, the average human being is between 1.5and 2 meters tall. So 1.5 meters would bea not-so-tall person, but 2 meters wouldbe quite tall. In fact, if you're 2 meterstall or above 2 meters tall, you might want toconsider basketball. So, for example, in thisdrawing right over here by Leonardo da Vinci, if this isan average-sized male, a meter, it would be more than halfway across his wingspan. So it might be about that much. And obviously, I am justroughly drawing this, just to give you a sense ofhow far a meter might be. And I just wrotea lowercase m here as really just a shortway of writing meter. So you could imaginethat the smaller things you might want tomeasure with the meter are things like a humanbeing-- a human being's height or a humanbeing's wingspan. If you wanted to say, well, whatare some of the larger things that you would want tomeasure with a meter, you might imagine somethinglike the height of a skyscraper. So this right over here isthe Empire State Building, at one time the tallestbuilding in the world, now just a tall building in the world. And this is 443 meters tall. So this is starting to be onthe larger scale of things that you would want tomeasure with a meter. Now you're probablyasking, well, what happens if Iwant to measure things that are even larger than that? Well the metricsystem provides us prefixes to essentiallysay multiples of meters. And the unit of distance thatis larger than the meter that is most typicallyused is the kilometer. I've heard a few people say"kill-O-meter," but kilometer, I'll pronounce is"kuh-LAW-me-ter," which is equivalentto 1,000 meters. And so when you'rethinking about kilometers, this is thinking about thedistance within a city. This would be even the distancefrom one city to another city. Even the radius of the planetis often measured in kilometers. And to once again get a senseof that, this right over here is a map of New York City. And right over herethey give us the scale. This distance right overhere is 5 kilometers. So 5 kilometers just togive us a sense of things-- and they wrote kmfor short so 5 km. This lowercase k, lowercase m isjust shorthand for kilometers, this would be equal to-- wellif 1 kilometer is 1,000 meters, 5 kilometers is goingto be 5 times as many. It's going to be 5,000 meters isthis distance right over here. If you were to try toimagine 1 kilometer, it would be 1/5 of that. So 1 kilometer on this mapmight look something like that. Now there's other unitsin the metric system that allow us to describe distancesless than a kilometer but more than a meter. But they're notas typically used. But I'll list them here, justso that you see that they exist. You have the "hect-O-meter,"or "heck-TOM-eter"-- it's so infrequently used thatI really haven't heard a lot of people say it-- whichis equal to 100 meters. And you have the "DECK-a-meter"or "deck-AM-eter," and I actually thinkit's "DECK-a-meter." Dekameter, which is 10 meters. And I'm going towrite these in orange because they're notthat frequently used. For example, it'snot typical to hear someone say that the EmpireState Building is 4.43 hectometers or for them to saythat this is 44.3 dekameters. They would typically saythat this is 443 meters. Now you're probably saying,OK, well, this is fine. Using these prefixeson the meter, I'm able to describedistances that are larger than a meter,that are multiples of tens of the meteror a multiple of 100 or a multiple of1,000 of the meter. But what if I wantto go smaller? Well, the metric systemhas units for that. And if we go just1/10 of a meter, this is not used astypically, but I'll write it here-- the decimeter. The decimeter is1/10 of a meter. Or another way ofsaying it is 1 meter is equal to 10 decimeters,lowercase dm for short. Once again, this isnot so typically used. But if we go onescale even below that, we get to the centimeter,which is a heavily used unit. And here, the prefixcenti means 1/100. So this is 1/100 of a meter. Another way of thinkingabout it-- 1 meter is equal to 100 centimeters. And if you wanted to imaginethe scale of a centimeter, you could imagine thisfrog right over here on this person's hand mightbe several centimeters long. So a centimeter on this drawingmight be around that distance. Now if you want to measurethings even smaller than that, we have anotherfairly common unit, and that is the millimeter. And the prefix millihere refers to 1/1,000. So it's 1/1,000 of a meter. Or another way of thinkingabout it is 1 meter is equal to 1,000 millimeter. Actually, let me justwrite m for short, just so we used to alsoseeing it that way. 1 meter is equal to1,000 millimeters. And if you wantedto imagine how long or how far a millimeteris, you could go down the scale of things that aresmaller than a centimeter. So these ants,for example, might be 3 or 4 millimeters long. So a millimeter in thisdrawing right over here might be something like that. The important thing to realizeor just to conceptualize is you might want to usedifferent units depending on the scale thatyou're measuring. And it's also usefulto just realize what these typical prefixesrefer to because we're seeing it used in distance here. They're all based on thebase unit of distance. But when we're measuring volumeor we're measuring other things in the metric system, thesesame prefixes also show up. So you see here whenwe're measuring distance, kilo refers to 1,000. A kilometer isliterally 1,000 meters. Hecto refers to 100. A hectometer-- 100 meters. Deka refers to 10. Deci refers to 1/10. So decimeter, literally1/10 of a meter. Centimeter-- 1/100,1/100 of a meter. Milli refers to 1/1,000.