Learning About Heat (1955)

thank you [Music] playing with snow is lots of fun [Music] but if you want to keep your hands warm you have to wear mittens or gloves because the snow feels cold take some snow into your bare hand the longer you hold it the colder your fingers get why is it because coal flows from the snow to your hands or because heat passes from your hand to the snow as people believed long ago if heat is an invisible matter that flows in or out of materials we should be able to weigh it this is the weight of a tray an ice cube and a cover the pointer shows zero all materials have weight in melting I should be losing weight does it there all ice is gone will the pointer show any loss of weight no evidently heat is not a material what then is heat it is a form of energy that can be used to do work that is to move things heat energy runs this earth-moving machine if heat is energy what is cope since heat is invisible let's try to answer this by using light when you remove light from the room you are not putting Darkness into it you are taking away the light similarly when you cool anything you are not putting cold into it you are taking away its heat in order to find out more about heat let's experiment again with ice like all other materials ice is thought by scientists to be made up of very tiny particles called molecules the molecules of all matter including ice are constantly moving the speed of molecules increases when heated so when we heat ice its molecules move faster and faster till those on the outside break away to form a liquid water if we continue heating the water its molecules will move even faster in boiling water molecules are rushing about so rapidly that some of them shoot off into the air as Steam which is a gas this experiment has shown that the same material can be a solid such as ice a liquid such as water or a gas such as Steam heat can also change the size of materials watch what happens when we heat The Wire the weight sinks the wire must have become longer when it cools off the weight Rises the wire becomes shorter again let's repeat the experiment using a different kind of apparatus we've seen that heat speeds up molecules when speeded up they push each other farther apart and cause the metal rod to take up more space this we call expansion and as soon as we stop the heating molecules slow down come closer together in the material shrinks this we call contraction let's continue learning about heat in a blacksmith shop when one end of the metal bar is heated the molecules on the heated end move faster they in turn make their neighbors move faster in this way heat passes from one molecule directly to the next this we call conduction metals are good conductors of heat the Smith can light a match on the end of the metal rod which is not in the fire because heat travels easily through metals in contrast some materials are poor conductors for example asbestos the Smith can put his hand safely into the fire when it is protected with an asbestos glove wound clothes are also poor conductors of heat air is another poor conductor but air can be heated in another way called convection here you see heated air carrying the tin foil upward and Below colder air is pulling the tin foil toward the flame this shows convection sometimes you see heated air above a lamp or above a radiator the heated air rises because cold air is heavier and pushes the warm air upward but the sun heats the Earth by a third means called radiation heat can travel by conduction and convection only if there is some material present raised from the Sun however must travel through empty space by this Third Way by radiation this is how it works the large bulb is giving out radiant energy air has been pumped out of the bulb even so when its radiant energy strikes the thermometer it is absorbed and changed into heat energy in this film we have explored several things about heat we learned that heat is a form of energy caused by the motion of molecules the faster molecules move the more heat energy there is in a material we saw that heat may change the state of materials from solids to liquids to gases that it causes materials to contract and to expand and that some materials are good conductors of heat and others are poor conductors next time you play in the snow think why we say that even snow and ice have some heat in them [Music]