Problem
“Wow, look at all these terrific books!” you exclaim as you skim over some of the titles in a cardboard box.
“Yeah,” your friend agrees, “but how are we going to get them to the library?”
It’s Book Donation Day at school.
A strong storm had swept through town a month ago. Part of the school had been damaged, including the library. No one got hurt, but the rain and wind ruined many of the books. So students, teachers, and parents organized a book drive to restock the library.
What a success! People have been dropping off boxes of books all morning at one of the school entrances. Heavy boxes of all sizes are stacked up and a dozen volunteers are ready to carry them to the library.
But the boxes are heavy—really heavy. The library is too far away to push or drag the boxes. And it’s hard for even two people to carry one. You and the other volunteers could leave the boxes and just carry a few books at a time, but that would take too long. There has to be a better way.
Solution
You think for a moment. “I’ve got it! Come on, we have to go to the Maintenance Office.”
Five minutes later, you and your friend are all smiles as you come walking down the hallway pulling two dolly carts. The volunteers easily stack the boxes on the dollies. Then it’s even easier to roll the boxes to the library, unload them, and head back for more. With everyone working together—and with the right tools—the job is done in no time. Well done!
It's Simple
What made the dollies such good tools for moving the heavy boxes? It’s simple! The wheels on the dolly are part of a simple machine. Like all machines, simple machines help us do jobs, usually by moving things faster, farther, or more easily than we can without the machine.
axle
wheel
axle
A dolly cart may not look like a typical machine. It’s not big and powerful like a car or a train. It doesn’t vroom! screech! or swoosh! like a lawn mower, a power drill, or a dishwasher. These are all complicated machines with lots of parts. Simple machines have no more than a few parts. In fact, some are made of only one part. Nearly every machine, no matter how complex, contains one or more simple machines. Think about a school bus. The hinges on which the doors swing open are levers. The stairs you climb to board the bus are a type of inclined plane. Screws might hold the frame of the seats to the floor. And of course, the wheels provide the smooth ride to school.
You can find wheels and axles on wagons and bicycles.
Machines That Go Round
If a machine turns in a circle, it is probably a simple machine called a wheel and axle. A wheel is a disc that turns round and round. You probably knew that.
Wheels don’t work by themselves, though. They have partners—axles! An axle is a rod connected to the center of a wheel. The axle connects the wheel to a vehicle. When the axle moves, so does the wheel, and so does the vehicle.
Wheels and axles make it easier to move things, like a wagon full of logs or a box full of books. Imagine pulling such a load without wheels. The bottom of the wagon would scrape against the ground. As you pull forward, the force of friction pulls in the opposite direction.
Wheels give you a big advantage in this tug‑of-war. There’s less rubbing and friction with wheels. Also, wheels roll. So, it takes a small effort from you to pull the wagon and keep it going.