1 00:00:00,560 --> 00:00:18,199 hello there and welcome to science class have you ever wondered why some objects 2 00:00:18,199 --> 00:00:27,640 sink to the bottom while others float in the water and there are others that 3 00:00:27,640 --> 00:00:34,320 float on the surface they go to the top in order to understand why this is 4 00:00:34,320 --> 00:00:39,759 happening we need to know everything about density why this is important and 5 00:00:39,759 --> 00:00:45,640 how can we calculate it open your books and come with me if you want to know 6 00:00:45,640 --> 00:00:51,600 everything about it a material or substance is matter with particular 7 00:00:51,600 --> 00:01:00,259 characteristics plastic wood and glass are examples of materials as you know 8 00:01:00,259 --> 00:01:07,159 materials have mass and volume they also have different properties these 9 00:01:07,159 --> 00:01:13,719 properties differentiate one material from another the density of a material 10 00:01:13,719 --> 00:01:21,700 is the amount of mass in a specific volume we can understand that by looking 11 00:01:21,700 --> 00:01:30,879 at this example these balls are objects made of two different materials in this 12 00:01:30,879 --> 00:01:41,209 case cork and steel they have the same volume because they occupy the same 13 00:01:41,209 --> 00:01:52,069 space they have different mass because steel is heavier than the cork so the 14 00:01:52,069 --> 00:02:02,950 steel ball has got more mass therefore if the volume is the same and the mass 15 00:02:02,950 --> 00:02:10,129 is different the density is going to be different as well because density is the 16 00:02:10,129 --> 00:02:18,819 amount of mass in a specific volume and this is what we need to know don't 17 00:02:18,819 --> 00:02:28,840 forget it density is the amount of mass in a particular volume I want you to 18 00:02:28,840 --> 00:02:46,949 have a look at this example bowling ball has got more mass 10 kilograms than the 19 00:02:46,949 --> 00:02:55,169 soccer ball that has got one kilogram since they have the same volume one 20 00:02:55,169 --> 00:03:07,520 liter we can calculate their densities easily bowling ball density is 10 which 21 00:03:07,520 --> 00:03:15,800 means that is heavier and denser than the soccer ball on the other hand the 22 00:03:15,800 --> 00:03:39,800 soccer ball is less dense than the bowling ball. Now that we know how to 23 00:03:39,800 --> 00:03:46,580 calculate density, you might be asking yourself why is density so important? Why 24 00:03:46,580 --> 00:03:52,580 do we need to know the density of the different objects? Well, pay attention and 25 00:03:52,580 --> 00:04:01,400 you will discover it. We can use density when we cook. We can use density to know 26 00:04:01,400 --> 00:04:10,500 if the material of one object is real or fake and most importantly we use density 27 00:04:10,500 --> 00:04:24,579 to know if an object floats or sinks did you realize that a large log of wood 28 00:04:24,579 --> 00:04:30,100 floated on water but a comparatively smaller piece of rock sank how is this 29 00:04:30,100 --> 00:04:35,860 even possible this is possible because of density the first case the log of 30 00:04:35,860 --> 00:04:46,939 wood floats on water because it has less density than water. However, in the second case, the 31 00:04:46,939 --> 00:04:50,620 piece of rock sinks because it has more density than water. 32 00:04:51,620 --> 00:05:07,860 In a container, the denser liquids go to the bottom, and the less dense liquids go to the 33 00:05:07,860 --> 00:05:15,660 top. Solid objects float in liquid that is denser than the object. If the solid object 34 00:05:15,660 --> 00:05:27,980 is denser it sinks this is called buoyancy according to this if i want to know if this 35 00:05:27,980 --> 00:05:35,579 state sinks or flows i need to know both densities because i have to compare them 36 00:05:36,860 --> 00:05:44,220 so i think we should do a scientific calculation here we can calculate the density of the water 37 00:05:44,220 --> 00:05:52,500 Density is calculated by dividing the mass and the volume. 38 00:05:52,500 --> 00:06:00,899 We calculate the mass using scales and beakers, and we discover that mass is equal to 100 39 00:06:00,899 --> 00:06:02,180 grams. 40 00:06:02,180 --> 00:06:11,120 Divide that by the volume, that is 100 milliliters, and as a result we can say that water density 41 00:06:11,120 --> 00:06:19,529 is 1 gram per milliliter. 42 00:06:19,529 --> 00:06:26,029 block sinks because its density is 2 which is more than the density of the 43 00:06:26,029 --> 00:06:37,819 water and this block floats because its density is 0 which is less than the 44 00:06:37,819 --> 00:06:49,339 density of the water and as you can see here objects can float in the water or 45 00:06:49,339 --> 00:07:04,529 or on the surface of the water depends on the density they have here is a table of densities 46 00:07:04,529 --> 00:07:14,050 of common items including several gases liquids and solids we can learn from it that metals 47 00:07:14,050 --> 00:07:25,699 usually sink cork floats or sugar is denser than water i've seen that you had some problems with 48 00:07:25,699 --> 00:07:30,579 with this exercise and I'm going to try to explain it. 49 00:07:30,579 --> 00:07:40,819 We need to know which substance is denser or less dense than another. 50 00:07:40,819 --> 00:07:45,120 Well there are two ways to find the answers. 51 00:07:45,120 --> 00:07:52,180 The first one is to do the experiment at home which is the best way to learn and the other 52 00:07:52,180 --> 00:08:22,689 one is to look up on the internet and find the density of the liquids well that's all for today 53 00:08:23,250 --> 00:08:28,449 i'll see you on no no no no wait a minute i have something for you 54 00:08:30,290 --> 00:08:37,490 it's a kind of a riddle i'm going to show you a picture and you have to answer to two questions 55 00:08:37,490 --> 00:08:46,490 1. How is this possible? 2. Where is this man? 56 00:08:46,490 --> 00:08:47,570 Have a look.