Simple Machines - Pulley And Its Types
Transcript
00:00Hi kids, today we will learn how a pulley makes our work easier.
00:09So let's start.
00:13We know machine is anything that makes our work easier.
00:20And machines can be a simple machine or a complex machine.
00:25Simple machine is a simple mechanical structure that is made up of no or few moving parts.
00:33Example a lever, a pulley, an inclined plane, a wedge or a screw.
00:42And complex machine is a machine that is made up of two or more simple machines.
00:49It can be a scissors, wheelbarrow, drill or just many.
00:55Whether it's a simple or complex machine, they give all of us some mechanical advantage.
01:02That is lesser force is required to do the work than doing it without the machine.
01:09We will learn a simple machine which is a pulley.
01:13A pulley is a wheel with an axle.
01:18Their edges of the wheel are grooved so that some rope can pass around this grooved edge
01:24of the wheel.
01:26And this rope is used to raise heavy objects.
01:31Pulleys can be used in many ways to lift loads.
01:36Now let's see what is the advantage of using pulleys.
01:42If you want to lift a very heavy object but your body cannot apply that much force, you
01:48can use this simple machine, pulley.
01:52Let's see how.
01:54You can attach the object to one end of the rope and let this rope pass through the grooved
02:01edge of the wheel.
02:04Now other end of the rope is free which can be pulled to lift the object.
02:12A pulley helps you to reverse the direction of your lifting force.
02:17So as in the picture below, you pull the rope downwards to lift the weight up.
02:24And if you want to lift something that weighs about 100 kg, you have to pull down with a
02:29force equivalent to 100 kg.
02:35If you want to raise the weight one meter into the air, you have to pull the loose end
02:40of the rope a total distance of one meter at the other end.
02:46So pulley changes the direction of force required to lift the object as you can see in the picture.
02:55You are not required to apply force in the direction in which you want to lift the object.
03:03It won't give you much mechanical advantage, that is, won't make your work much easier.
03:09But the more the number of pulleys, the lesser the amount of force required to do the work.
03:15We will learn more about it later.
03:19Pulleys are of two types.
03:22They can be fixed pulleys and movable pulleys.
03:26Fixed pulleys are those where the pulley is tied to a bar or beam and the pulley doesn't
03:32move at all when the rope is pulled.
03:36It just changes the direction of the force and there is no multiplication of force.
03:44If you lift something without a pulley, you are required to apply force in an upward direction.
03:51And when you use a pulley, the direction of force changes and now the direction of force
03:57required is downwards.
04:00And it's easier to apply the force in a downward direction than applying in an upward direction.
04:09Now let's see what is movable pulley.
04:13In case of movable pulley, pulley is not tied to any beam or bar.
04:22One end of the rope is tied to the fixed beam or bar.
04:26Other end is free to be pulled by any other person.
04:31And the pulley is in the center to which the object is attached.
04:36This way, the weight of the object is shared between the fixed bar and the person pulling it.
04:45It is a pulley that moves along with the load.
04:48That is, both the pulley and the load is movable.
04:55The load moves in the direction of force applied.
04:58It takes less force to lift or move the object than moving with your hands only.
05:07And the more the number of pulleys and supporting ropes, the smaller the force required.
05:12So a movable pulley multiplies the force.
05:17Now let's see what is a compound pulley.
05:22Compound pulleys are also called block and tackle.
05:26A compound pulley is a combination of a fixed and one or more movable pulleys.
05:33A simple pulley only redirects or changes the direction in which force is applied and
05:41does not give us much mechanical advantage.
05:47But a compound pulley or a block and tackle pulley is able to reduce the effort required
05:54to do the work.
05:56Example, if the work involves lifting a 100-pound weight, a compound pulley made up of two pulley
06:04wheels and a longer rope reduces the lifting force to only 50 pounds.
06:11More greater reductions are possible with more number of pulley wheels and longer threads.
06:19But these systems take a lot of space.
06:24So kids, today we learned a lot about pulleys.
06:29We learned pulleys are of two types, fixed pulleys and movable pulleys.
06:37And we also learned that a single pulley does not give us mechanical advantage, that is,
06:43does not reduce the amount of effort required, but only changes the direction in which the
06:50force is required to be applied.
06:54But compound pulleys, that is, where more number of pulleys are there, gives us some
07:01mechanical advantage, that is, they reduce the amount of force required to do the work.
07:08Now you may go ahead and take a quiz to learn more.
07:12Bye-bye!