Explaining Matter - Molecules in Motion (1959)

[Music] this world of ours has been studied by scientists for many many years one of their most important ideas is that all material consists of molecules which we're going to talk about in this film by observing things around you like water and Rain you can learn something about molecules yourself not only at school but at home or wherever you happen to be let's watch Jim and Alice as they do a very simple experiment they put this glass of water where they can leave it for a whole week with our eyes we can't see anything happening to this water but with a special camera that speeds up a week's time we can watch it [Music] disappear so a week later Jim and Alice find all the water gone of course you expected this you already know about evaporation but have you ever asked yourself just what really happens when water evaporates let's suppose that water evaporates because tiny bits of water are always escaping into the air one by one we call them molecules which means very small if we suppose that molecules are escaping then we must also suppose that they're moving we're using these black dots for water molecules and white dots for air molecules but actually molecules are so small that billions and billions of them are in the smallest drop you can see let's suppose that these molecules are always moving around each other and that the faster ones fly off into the air and that this is evaporation let's go on with our idea about molecules Jim is adding some coloring to this water so that the water can be seen better as you know water has no shape of its own but takes the shape of its container we call water a liquid if in addition to Having no shape of its own a liquid always takes up the same amount of space that is it always has the same volume but now let's freeze some water in a glass we no longer have a liquid because ice though it does have a definite volume does not change its shape as water does when we take the ice out of the glass it still keeps the same shape a material which has a definite volume and also a definite shape is called a solid can the idea of molecules help us explain what has happened here let's imagine that cooling slows down the movement of molecules until they stop moving around each other as they do in a liquid and hold their positions to form a definite shape and size that is a solid in a warm place the molecules begin to move faster and the ice melts as the molecules begin to move around each other again thus they again form a liquid water if we hate this water you know it will boil but do you know what boiling means as water is heated let's suppose the molecules move faster and faster until they begin to fly away from each other and form the bubbles we see Rising into the air as gas some of the gas collects into tiny droplets we see as Steam each droplet of steam contains billions of molecules a gas has no definite volume and no definite shape its fast moving molecules spread out and fill whatever space is available to them does it surprise you that water can be an invisible gas when you take a cold glass out of the refrigerator what happens you find a mist of water collects on it water that can only have come out of the air so we find that the idea of molecules in motion can explain what we call physical change that is the change of a material into three different forms solid liquid and and gas can the idea of molecules explain other things beside physical change get your parents permission to put a jar with a presson cap into a pan of cold water don't use a screw cap heat the water slowly and be sure to stand away you can probably guess what will happen what caused the cap to blow off let's suppose that what we call pressure is actually the force of molecules striking against a surface when we close the top of the jar there are just about as many molecules striking the inside as the outside so the pressure inside is just about the same as the pressure outside remember we suppose that heat makes the molecules move faster as the jar heats up the molecules keep striking with more and more Force against the inside of the jar the pressure outside Remains the Same all around including the top but the pressure inside increases until can we increase pressure without using heat well when we pump up a balloon what are we really doing we're adding more air molecules this means that more molecules strike the inside of the balloon than the outside this increases the pressure inside and pushes the balloon out so we find that the idea of molecules explains many familiar things butter is a solid when it's cold but when it's heated it quickly melts and turns into a liquid nearly always physical change is connected with heat maybe you've seen your mother pour melted paraffin over the top of jelly glasses when hot it's a liquid and looks much like water but when it cools it becomes a white solid even such things as iron and rocks melt and become liquid when they're hot enough and will become gas if they're made even hotter whether a material is solid liquid or gas depends most ly on its temperature some materials you usually find as a gas at ordinary room temperatures the bubbles in ginger ale are caused by a well-known gas called carbon dioxide soda fonds get this gas in a tank and mix it with water in making ice cream sodas but here is carbon dioxide that is solid because it's so very cold it's often used to keep ice cream cold you probably know it as dry ice this cup contains liquid air since air is a gas at ordinary room temperatures it must be made very cold before it will become liquid if we dip a rose into this very cold liquid air it undergo a physical change it freezes and becomes hard and brittle so although we've never seen most molecules we know they exist because they help us explain so much about the behavior of materials around us why a solid has definite volume and definite shape why a liquid has definite volume but no definite shape and why a gas has neither definite volume nor definite shape they explain pressure as the force of molecules striking against a surface and why pressure may be increased by [Music] heat or by adding more molecules these are just a few of the facts explained by one of the most important ideas in science the idea of molecules in motion [Music] the e e e e e e e e e e e e e e e e e e