12 30 الكثافة Density

today we're going to talk about density and we're going to answer the age-old question just how dense is Dr Carlson first let's talk about what density is okay density is measurement of the substance and we want to know how much mass it has which kind of has to do with how heavy it feels and how big it is how much volume it takes up those two things together tell you something's density okay The more mass you pack in smaller space the more dense something is so for instance have five Metals right here have aluminum okay and have 10 and zinc all right and copper and little piece of lead and all five of these pieces of metal have the exact same mass okay and as you can see most of them are different sizes okay and density is actually calculated using algebra or whatever all you do is you take the mass and you divide by the volume so here we would take this mass and divide it by big volume and it would have smaller number for density than this lead here take its mass which is the same as this but you divide it by much smaller volume and so this would have very big density okay and so quick and easy way to find out something's density to compare it to is to throw it in water water turns out to have density about 1 per milliliter and so if it sinks it turns out that that thing is going to be more dense than water and if it floats it's less dense than water all right so again the two things we need to know is that you need to know how much mass something is and what its volume is and those two put together will tell us its density and the cool thing about density is that it doesn't ever change if you break things up into little parts for instance this aluminum rod would have the same density if broke it in half if just measured one half of this Rod it would have the same density as the entire Rod okay because if broke it in half just measured half of the rod it would half have half the mass and would have half the volume and so if you figure out the math on that it turns out to have the exact same density as measuring the whole Rod okay so let's go find out how dense am all right you need remember you need to know two things to know something's density you need to know its mass and you need to know its volume and usually we do mass in grams and volume in milliliters or you could do kilograms and liters something like that so let's find out what my Mass is and we can do that using scale step on the scale it says right about 71 kg so so we found out my mass which is 71 kg now we need to know my volume and we'll know my density okay just take the mass divided by the volume well we're going to use method that aredes first used which is when you climb into the bathtub you can see that the water level goes up and so when you get out of the bathtub the water level goes back down if you measure how much the water level goes up and back up then you'll know how much volume you take up so have garbage can full of water okay and I'll get in and I'll displace bunch of water lot of water will come out then when get out we'll fill it back up the top and however much water it takes to refill it will be my volume so here we go nice cold water yeah that feels good so we're displacing water here all right take some water and okay good stuff so however much water I've displaced that is my volume so now let's go and measure it so so now if we add up the volume of all the buckets that have water that pour in trash can it adds up to be 69 of water so to find my density we take 69 well actually we take 71 kg and divide it by 69 and that's just little bit more than one about 1 Point 1.01 1.02 somewhere in there I'll figure that out so anyway so it's just over density of 1 kilogram per liter and it also works out to being about 1 gam per milliliter and the interesting thing about that is that water has that same density okay and since I'm just little bit more dense than water little bit over one that should mean that sink in water and do when blow out all the air in my lungs which think did when was in there then my my density less than it's more than water and sink all right and so you can quickly find whether you are more or less dense than water by getting in in pool and blowing all all your air and see if you sink or float all right and that should work out because most of your body is water so you'll be right around water so if you want to really guess your volume just find your mass in kilograms all right so enjoy playing with density and remember that Dr Carlson is dense and have density just over one and I'll know my volume so here it goes nice and yeah there you go in this and it's no sck way I'm get in this this is not have to get bigger garbage kid