Problem
“Wow, look at all these terrific books!” you say, as you skim over some of the titles in a cardboard box.
“Yeah,” your friend says, “but how are we going to get them to the library?”
It’s Book Donation Day at school. A strong storm swept through town last month. Part of the library was damaged. No one got hurt, but the rain and wind ruined many of the books. So students, teachers, and parents organized a book drive for the library.
What a success! People have been dropping off boxes of books all morning. Heavy boxes of all sizes are stacked up, and a dozen volunteers are ready to carry them into the library.
The boxes are too heavy to push or drag. 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 come walking down the hallway pulling two dolly carts. The volunteers stack the boxes on the dollies. Then they 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.
It's Simple
What made the dollies such good tools for moving the books? It’s simple! The wheels on the dolly are part of a simple machine. Simple machines help us do work by moving things faster, farther, or more easily than we can without the machine.
axle
wheel
axle
Simple machines have no more than a few parts. Some have just one part. Nearly every machine is made up of one or more simple machines.
Think about a school bus. The door’s hinges are levers. The stairs are a type of inclined plane. Screws hold seat frames to the floor. And of course, the wheels provide the smooth ride to and from school.
You can find wheels and axles on wagons and bicycles.
Machines That Go Round
A wheel and axle is a simple machine that turns in a circle. A wheel is a disc that turns round and round. But wheels don’t work by themselves. 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.
Imagine pulling a load of logs on a wagon without wheels. The bottom would scrape against the ground. As you pull forward, the force of friction pulls in the opposite direction. Wheels roll. There is less friction. So, it takes less effort from you to pull the wagon.