In today's video we're going to take a look at the different units of length and see how we convert between them. We'll also run through some examples of really tiny things like atoms and cells so you can try to get an idea of how big they really are. Let's start off with a scale stretching from nanometers, which is the smallest unit you need to know, to micrometers, millimeters, meters and kilometers.
The reason we use these units is that each one is 1000 times bigger or smaller than the one next to it. For example, a kilometer is 1000 times bigger than a meter, and a nanometer is 1000 times smaller than a micrometer. Now, converting from one unit to another can be a bit confusing, so let's take the example of 6 millimeters and convert it to all of the other units. The general rule is that if you want to convert a particular value into a larger unit, then you have to divide the number by 1000 for each place that you want to move it up the scale.
So to convert 6 millimeters to meters, we divide the number 6 by 1000 to get 0.006 meters, or 6 times 10 to the minus 3 meters. Notice here that we're making the number smaller. but the overall value is staying the same because the units are larger.
So 6mm and 0.006m are exactly the same value. Then to convert it to kilometers, we divide the 0.006 by 1000 to get 0.00006km, or 6 times 10 to the minus 6 kilometers. On the other hand, if we want to convert something to a smaller unit, we just do the opposite and multiply the number by 1000 for each place you want to move down the scale.
So to convert 6mm to micrometres, we'd multiply the 6 by 1000 to get 6000 micrometres, which we can also write as 6 times 10 to the 3 micrometres. Then to convert it to nanometres, we just multiply it by 1000 again to get 6 million nanometers, or 6 times 10 to the 6th nanometers. Now if you want to convert units that aren't next to each other on the scale, like converting 340 nanometers to millimeters, then you could just do it in one step, and in this case that would mean dividing it by 1 million, but I think it's much easier to just divide it by 1000 to get it into micrometres, and then divide it by 1000 again to put it into millimetres. So if we do it that way, the 340 nanometres would become 0.34 micrometres, and then it would become 0.00034 millimetres, which is 3.4 times 10 to the minus 4 millimetres. To give you a better sense of how big all of these units are, Let's take a quick look at the size of some common objects.
If we start with the smallest, atoms range from around 0.1 to 0.5 nanometers across, whereas medium-sized molecules like glucose are about 1 nanometer across. Then viruses might be 100 nanometers or so across, small cells like bacteria could be a micrometer or so, most animal and plant cells are in the 10-100 micrometer range, and human hair is about 100 micrometers wide. Then it gets to the familiar stuff like insects, books, planes, and mountains.
So if you had nothing but the naked human eye, we'd better see all the way down to about 100 micrometers. So the smallest thing we could see is the width of a human hair. If you had a light microscope though, like the ones that you might have used in class, then you'd be able to see all the way down to 500 nanometers or so. And if we used special microscopes called electron microscopes, then we'd be able to see all the way down to about 0.1 nanometers. Don't worry about remembering any of these specific numbers or examples.
This was just to give you a bit of context to help you understand these tiny units. The very last thing I want to cover is centimetres, which sit just here on our scale, between millimetres and metres. A centimetre is equal to 10 millimetres, and there are 100 centimetres in a metre.
So to convert from centimetres to metres, you divide the number by 100. Or to go from centimetres to millimetres, you multiply the number by 10. If you're given centimetres in a question, it's probably always easiest to multiply it by 10 first to put it into millimetres, and then from there convert it to whatever else you need. For example, let's convert 30cm to nanometres. First, we times the 30 by 10 to get 300mm, then by 1000 to get 300,000 micrometres, and then multiply by 1000 again to get 300 million nanometres, or 3 times 10 to the 8 nanometres. And that's everything for this video.
So if you want to practice questions on this topic or anything else in science or maths then click on the link in the description below or in the pinned comment and that'll take you directly to our platform where you can view the lesson for this video. So you can practice questions on all this stuff that we've been covering and just double check that you know it all.