How Levers Help Us (1970)

[Music] you probably know what this man is using it's a carjack and with it a person can lift one end of a heavy car clear off the ground a car jack is a lever levers help us do work to make to make the parts of this lever easier to see let's change it from a car jack to this now you'll see that a lever has a part that moves and a place for that part to move on when one end of the lever moves down the other end moves up now let's notice something else about this lever think about the place that the lever moves on and think about the part of the lever that's on one side of it and the part that's on the other side notice how long one part of the lever is notice how short the other part is now watch the two ends as the the lever is used while the end of the long part is moving a long distance the end of the short part is moving a short distance now let's watch the lever being used again but this time we'll think of how hard it is for the man to lift his car he doesn't have to push very hard on the long end his easy push down on the long end is changed to a hard push up on the short end you see he's lifting his car you've learned two things about this lever now a push down on one end is changed to a push up on the other and an easy push at the end of the long part is changed to a hard push at the end of the short part that's what happens when we use a carjack the handle is the long part of the lever you can't see the short part and easy push down on the handle makes the short Part push up hard hard enough to lift the car a little the jack is built so that each push down on the handle lifts the car up higher and higher the man's hand on the long part of the lever moves a long distance up and down the car on the short part of the lever moves just a short distance the jack is a lever that helps the man lift a very heavy car when we make the long part of the lever even longer what will happen it's easier for the man to lift the car but notice the end of the long part of the lever moves up and down much farther now a greater distance than it did before what will happen when we make the long part of the lever still longer it's easier than it was before to lift the car but look how far the end of the long part of the lever has to move the longer the long end is the easier it is to push it down and lift the car up we can make the long part of the lever as long as we want the longer it is the easier it is to lift the car that is if you can reach the end of the long part you have to be able to use a lever for a lever to help you now we're being silly you wouldn't ever do this we use levers to help us in all sorts of ways ways you can pull a nail out of a board like this a lever doesn't have to be straight it can be curved like a crowbar but it still has a part that moves and a place to move on a hammer is a lever when it is used to pull a nail from a board no matter how levers are shaped they're all alike in at least two ways a lever has a part that moves and a lever needs some place it can move on and because one part of the lever is longer than the other an easy pull at the end of the long part is changed to a hard pull at the end of the short part pulling out a nail is easy with a lever but without a lever well you try it sometime when you use a shovel to dig up dirt is the shovel a lever well it has a part that moves and it has a place that part can move on and because the part on one side of this place is longer than the part on the other side an easy push at the long end is changed to a hard push at the short end and dirt is pushed up out of the ground yes a shovel is a lever now when you use a lever you don't always have to push or pull on the long end think of rowing a boat with ores are ores levers The Ore is something that moves and there's a place the ore moves on part of the ore is on one side of this place part of the ore is on the other side an ore is a lever but do you pull on the long part of this lever no you pull on the short part your hands move the lever back and forth your hands move the short end of the lever the long end of the lever moves the boat no matter how far you move the end of the short part of the lever the end of the long part moves farther so this lever doesn't change an easy pull into a hard push it changes a short movement into a longer movement and that's what you want when you row a bolt with a lever a lever has a part that moves and a place for that part to move on sometimes we push or pull at the long part of the lever we do that when we want to change an easy push or pull to a hard one sometimes we push or pull at the short end of the lever that is when we want to change a short movement to a longer movement which part we use just depends on what kind of help we need sometimes we put two levers together to help us a scissors is a pair of levers used together this scissors is good for cutting things like paper or cloth that are soft and thin our fingers push on the short parts of the levers that moves the long parts of the lepers they come together and cut so our fingers push the handles on the short ends of the levers for easy cutting but suppose we wanted scissors to cut something hard and tough like metal where would we put the handles then that's right on the long ends of the levers now an easy push on the handles is changed to a hard push on the blades and a hard push is what we need to cut through tough metal often levers are parts of other machines this power shovel uses several levers for instance this part is a lever why the arm of the shovel can move and it has a place it can move on there are many kinds of levers that help us in many kinds of ways do you see levers here levers help a piano play look inside someday and you'll see [Music] how levers help us change easy pushes to hard pushes is this a lever yes a push up on one part of a lever can be changed to a push down on the other part it isn't hard to see how levers help us