Movable Pulley Definition: Lesson for Kids

Instructor: Mary Beth Burns

Mary Beth has taught 1st, 4th and 5th grade and has a specialist degree in Educational Leadership. She is currently an assistant principal.

What do elevators, cranes and weight lifting machines have in common? Come and find out in this lesson where we will explore one particular kind of simple machine and its advantages and disadvantages.

What Is a Movable Pulley?

Pretend that you are at the bottom floor of a giant skyscraper. You need to get to the 25th floor of the building. What is the best way to do this? Sure, you could take the stairs (which would be an excellent source of cardio), but that is going to be a lot of hard work and will take you a long time. Another option would be to take the elevator, which can pull you up to the 25th floor in less than a minute. How is the elevator able to move you so fast? Because it has a giant movable pulley inside of it.

B is the movable pulley, W is the load and C is a fixed pulley

Like other types of pulleys, movable pulleys are made of a wheel and rope. The wheel has a little divot, or groove, around it where the rope can fit inside (kind of like the way a hot dog rests in a hot dog bun). While that might not sound like much, a pulley makes it much easier to lift heavy loads (or objects that need to be moved). What makes a movable pulley unique is that only one part of the rope is attached to a fixed object, like a bar or a beam. When both parts of the rope are attached to a fixed object, this is known as a fixed pulley. Fixed pulleys do not move with the load like movable pulleys do.

Real World Examples

Movable pulleys are all around us! As we mentioned before, elevators are real-world examples of movable pulleys. You might be thinking, 'Well, I haven't seen a pulley in the elevator before...' This is because it is not inside the part of the elevator that you stand in; rather, it can be seen inside the elevator shaft. Please do not take this as a suggestion that you should peek inside the elevator shaft to look at the movable pulleys. That is very dangerous and a bad decision.

Can you see the movable pulley in this elevator shaft?

Do you know someone who enjoys lifting weights at the gym? Many of the weight lifting machines have movable pulleys inside them as well. This allows the person working out to use less effort to lift a given amount of weight, which helps them to work out safely and avoid injury. Cranes (the big machines that you might see at a construction sight) are movable pulleys as well.

A crane is an example of a movable pulley

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