“Wow, look at all these books!” you say. It’s Book Donation Day at school. Students, teachers, and parents have been dropping off boxes of books all morning. The boxes are really heavy. How will you get the books inside?


You come up with a great idea! You go to the Maintenance Office and borrow a dolly cart. Now, volunteers can stack the boxes on the dolly. Then it’s easier to roll the boxes to the library. Well done!

It's Simple

What made the dolly such a good tool? It’s simple! The wheels are part of a simple machine. Simple machines help us do work. They move things faster, farther, or more easily than we can without them.




Simple machines have no more than a few parts. Some have just one part. Nearly every machine has one or more simple machines.

You can find wheels and axles on wagons and bicycles.

Machines That Go Round

If an object 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. An axle is a rod. It is at the center of a wheel. It connects the wheel to a vehicle, like a bike. When the axle moves, so does the wheel. And so does the bike.

Imagine pulling a load of books without wheels. It would scrape the ground. As you pull forward, the force of friction pulls in the opposite direction. Wheels roll. So, there is less friction. With wheels, it takes less effort to pull.