Key concept (the Science of Simple Machines): A pulley is a wheel that you loop a rope over. The key point of pulleys is that they redirect force. For example, instead of PUSHING a load UP, you can attach it to a rope and pulley above you and PULL DOWN. All pulley systems re-direct force. Some pulley systems make work easier, allowing a worker to use less force to move the object.
- Tie a rope on something heavy (e.g. a basket of books, a sack of flour, or a 2-liter bottle of soda).
- Have a child lift the object off the ground by pulling up on the rope. They may only be able to lift it six inches or so off the ground – partially because it’s heavy, partially because their little arms can only reach so high.
- Then have them pick up the object itself and try to lift it high up above their head. It’s higher now, but wow it feels heavy to push it up.
- Then, string the rope up over the back of a chair or over a doorknob and have them pull down on it. It feels easier* to pull the rope down to lift the object than it did to push the object up with their hands. But they can only lift is as high as the pulley.
- Then throw a rope over the side of a slide platform (or around a railing on an open staircase: http://handsonaswegrow.com/simple-machines-for-kids-the-pulley/) and put a kid up there to reel it in. Look how high you can lift something when you use this tool!
Notice that none of those examples use an actual “pulley” from a store – they used a chair or doorknob, a slide platform or a stair railing. You’re getting pulley action just by wrapping a rope around an object and pulling.
You can also rig a “pulley” with other objects you may have:
- A rolling pin pulley: http://cabinetofcuriositiesva.com/2014/08/21/a-lesson-on-simple-machines-simply-worked/)
- A spool that cord or ribbon was once wound around: https://gosciencegirls.com/pulley-loungeroom-stairs-physics-fun-kids/.
- Carabiners: www.youtube.com/watch?v=oGgCaFTcbHk
- A spool for thread and a wire hanger: www.ehow.com/how_5896241_make-pulley-children.html
If you want to buy a basic pulley set for your kids, I think it’s a great investment in a fun toy they can use in a variety of ways for a number of years. The ones we used in class are Block & Tackle Pulley Kit (also available from Magic Cabin Toys). They were good for our purposes, although I strongly recommend using utility cord from the hardware store rather than the thin string from the kit, because it will be gentler on children’s hands and less likely to jump off the pulley. The kit came with a book on activities to teach kids about pulleys, so that was nice. We also considered (but I haven’t tested) Pulleys Discovery Kit and American Educational 7-1607 Pulley Kit. Or, you could get a Clothesline Kit.
We’ve recently inherited some pulleys from a Delta Science Modules kit.
Set up a variety of pulley systems:
The clothesline. Requires two pulleys. Attach pulleys to anchor points. Take a rope, and tie one end to a basket, then loop it around both pulleys, and tie the other end to the basket so you have a continuous loop with a basket mounted on it. (Or, if you prefer, you could just have one loop of clothesline and put a clothespin on it… you could then clip on messages to send back and forth.) Then you pull on either the top of the bottom cord to bring the basket from one end to the other. This is easy for even two year olds to do, but still plenty of fun for our elementary aged kids.
- Some ideas for anchor points: at home, we tied one end to a high stair railing, and one end to a chair. In class, we tied one end to the slide platform and one end to a step ladder. Next year, I plan to set this up somewhere different in the classroom – both years, we’ve had it on the slide platform with several other pulley systems. This one doesn’t need the height of the slide platform, so moving it elsewhere will help to spread out the pulley activities to different spaces. It could just string from one chair to another.
- To really engage kids in this activity, make it a message delivery system – our students LOVED sending messages to Teacher Cym.
A fixed pulley. Requires one pulley, and a high place to anchor it. You anchor the pulley, tie a rope onto a bucket, run the rope up over the pulley and back down to the ground. A child standing on the ground pulls on the loose end of the rope (shown with the red arrow above, and it lifts the basket high.
- This activity is more fun if the high anchor is next to somewhere a child can stand, like on a slide platform, or on a stair railing, or tree house or the top of a ladder. That way, one child on the ground, pulling the rope to raise the load up to their buddy on the high platform.
Moveable pulley. Requires one pulley. (We didn’t use this in class.) Tie a rope up high, run it through a pulley with a load hanging on it, then bring the end of the rope up high. Pull the rope up to bring the load up.
Compound pulley. Requires two “pulleys” – it’s basically a combination of a moveable and a fixed pulley. Note: we didn’t have enough pulleys, so we cheated. Instead of attaching a pulley on the bucket, we just looped the rope through the handle of the bucket so it could run through it like it would run through a pulley. So, we tied the rope high, ran in through the bucket handle, then through a pulley up high, then left an end of the rope dangling down. The child could pull down on the rope. We just had this set up along a wall, and it didn’t engage children as much, because we didn’t have anything special to lift up in it, and they weren’t lifting things up to a buddy.
A basket on a track. We threaded a cord through the handles of the basket so the basket could slide back and forth on the cord. We tied one end of the cord up high (on a slide platform or a stair railing) and the other down low (on a step ladder or a chair.) This cord is represented by the yellow line above, and it forms the track the basket travels on. Then we mounted a pulley near the top end of that cord. We tied one end of a rope onto the basket, ran it up and over the pulley, and down to the ground. When a child pulled down on the rope, it pulled the basket up to the top of the cord. If the basket is heavy enough, then when the child lets go of the rope, the basket will slide back down to the bottom of the cord. Note: this is one system that still needs work. It was hard to get the basket to glide well on the cord, and hard to weight it just right so it could be pulled up and would then slide back down. Next year we MIGHT trade the basket for some kind of gondola on a track.
Block and Tackle. There are lots of variant on block and tackle. The simplest is shown above. Block and tackles reduce the amount of work required to lift a load, because they distribute the work over multiple pulleys.
Here are pictures from class. I apologize for their quality. It’s hard to get a good picture of pulleys and ropes!
Here’s the top of the clothesline (above) and the top of the basket on a track (below) where they attached to the slide platform. (Click on it to see a larger image.)
Here’s our compound “pulley” system, using the basket handle as the second “pulley.”
Here’s our block and tackle system, set up on a ramp.
Understanding force: In step #4 of our initial demonstration, we said if feels easier* to pull down on it. This is just a body mechanics sensation not a measurement of actual total “work” needed. That step was basically setting up a fixed pulley system, and with a fixed pulley, you need to use the same amount of force, the pulley just redirects your force.
The moveable pulley reduces the amount of force needed to lift the basket. The compound pulley reduces it even more as does the block and tackle. This Explain that Stuff article does a nice job of explaining the basics of force and pulleys at an adult level. The Wikipedia article on pulleys has good descriptions of block and tackles.
Math activity: Put weights into each of the baskets. Dominoes? Glass pebbles? Books? Depends on how strong your baskets, your rope, and your child. Count how many of that object you can lift with each type of pulley. Which helps you do the most work?
Water table: My husband built a wishing well from Duplos, thread, and a plastic cup. Note: this requires some specialty Duplo pieces which we got from our Duplo Simple Machines pack. A pulley lifts the bucket up out of the water. These are views of the full well, the front of the pulley, and the back. (Click for larger image.)
Challenge Activity – Build a Flagpole System. We put out straws, binder clips, spools, bobbins, string, and clay, and encouraged children to try making a flag pole. We also offered a couple samples we had assembled. This project was over the head of most of our preschool aged kids, but our older kids and parents had fun with the challenge.
Art project: Flagpoles use pulley systems to raise the flag. We had the children decorate paper flags with markers. Next to this station, we put posters showing the flags of all 50 states, and most countries, to serve as inspiration for the activity.
In the morning class, we basically did the demonstration of pulleys exactly as described at the top of this post, using one child as our volunteer to demonstrate the work.
In the afternoon class, we did it a little differently. We set up a ramp (inclined plane) using a long plank propped up on a step ladder. At the bottom of the plank, we set a basket full of two stuffed elephants. We tied a rope on the basket, ran it through a pulley attached to the step ladder, and back down. (A fixed pulley.) We had the kids haul on the rope to pull the elephants up the slide. It was HARD work! They had to learn how to brace their bodies to pull hard (a good large motor skill to learn!) Some kids would just pull on the rope and keep backing up further and further. Some understood how to pull hand over hand, so they could stand in one place and alternate hands to pull with. (Pulling hand over hand is also a great large motor skill to learn.) They were putting so much force into their pulling that an adult had to brace the ladder so it wouldn’t tip over.
Then, while I read the day’s book (Raising a Bag of Toys: Pulley vs. Inclined Plane), my co-teacher re-rigged the pulley system so it was a block and tackle attached to the basket of elephants. After the story, we had them all try pulling the elephants up again. It was SO MUCH EASIER for the kids to do. (And no need for an adult to brace the ladder.) This was a fabulous hands-on experience that really helped them appreciate the power of the block and tackle.
Next year, I think in opening circle, we’ll do the initial demonstration of the pulley idea, and in closing circle do the block and tackle demo.
Follow-Ups to Extend Learning
Set up your own pulley systems at home. As I mentioned above, you don’t HAVE to buy pulleys to do this. You can use a rolling pin, spools or bobbins, or carabiners, or even just a rope looped over a stair rail, a bunk bed rail, or the back of a chair. Let your child play with them. (Some kids can get caught up for hours in the simple process of loading a bucket and hauling it up to a high platform.)
Here’s a fun craft to make with recyclables: build a winch system: http://littlebinsforlittlehands.com/
Song: I didn’t really find a song that was good for this age group to sing… but for the entertainment and amusement of adults or older kids, check out “The Sick Note / Why Paddy’s Not at Work Today”: www.youtube.com/watch?v=iA5RGI3zn20
For a great collection of pulley activities for kids, including recommended books, click here: http://iijuan12.hubpages.com/hub/gears-and-pulleys-simple-machines-lesson-plan. Here are a couple fun posts about how parents added pulley play to their backyards for hours or years of fun for their kids: http://handmadekidsart.com/backyard-pulley-engineering-kids/; http://happyhooligans.ca/a-bucket-and-a-rope/; and http://littlebinsforlittlehands.com/homemade-outdoor-pulley-play-idea-simple-machines/
Here is an image showing the four main types of pulleys, and here’s a PDF mini-poster you can print of all 6 types of pulley systems I describe.
Note: All the activities described in my posts are from Family Inventor’s Lab, a parent-child cooperative class in Bellevue, WA. We are a play-based, STEM focused class for preschool through early elementary (kids age 3 – 7). We do a wide variety of fun, hands-on activities to learn about Science, Tools, Engineering, Nature, and Art. We also sing songs and read stories. Most of our activities are cheap, easy, and use everyday materials that most families would have in their homes (or their recycle bins!), so that our activities are appropriate for classroom teachers, parents who homeschool, or after school programs.