[Music] 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 the 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 1,000 times bigger or smaller than the one next to it for example a kilometer is 1,000 times bigger than a meter and a nanometer is a thousand 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 mm 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 1,000 for each place that you want to move it up the scale so to convert 6 mm to Meers we divide the number six by 1,000 to get 0.006 M or 6 * 10us 3 m notice here that we're making the number smaller but the overall value is staying the same because the units are larger so 6 mm and 0.006 M are exactly the same value then to convert it to kilometers we divide the 0.006 by 1,000 to get 0.006 km or 6 * 10- 6 km on the other hand if we want to convert something to a smaller unit we just do the opposite and multiply the number by 1,000 for each place you want to move down the scale so to convert 6 mm to micrometers we multiply the six by 1,000 to get 6,000 micromet which we can also write as 6 * 10 3 micromet then to convert it to nanometers we multiply it by 1,000 again so you get 6 million nanom or 6 * 10 6 nanom now if you want to convert units that aren't next to each other on the scale like converting 340 nanom to millimet 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 1,000 once to get into micrometers and then divide by th000 again to put into millimeters so if we do it that way the 340 nanom would become 0.34 microm and then it would become 0.0034 mm which is 3.4 * 10- 4 mm 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 mediumsized molecules like glucose are about 1 nmet 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 to 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' better see all the way down to about 100 micromet so the smallest thing we could see is the width of a human hair if you had a lik microscope though like the ones that you might have used in class then you'd be a to see all the way down to 500 nanometers also and if we used special microscopes called electron microscopes then we'd see all the way down to about 0.1 nanom 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 centimeters which sit just here on our scale between millimeters and meters a cm is equal to 10 mm and there are 100 cm in a meter so to convert from centim to meters you divide the number by 100 or to go from centimeters to millimeters you multiply the number by 10 if you're given centimeters in a question it's probably always easiest to multiply it by 10 first to put it into millimeters and then from there convert it to whatever else you need for example let's convert 30 cm to [Music] nanometers first we times a 30 by 10 to get 300 mm then by 1,000 to get 300,000 microm and then multiply by 1,00 again to get 300 million nanom or 3 * 10 8 nanom 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 will 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