Problem
“Wow, look at all these books!” you say, as you look at all the cardboard boxes.
“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 had swept through town. Part of the school was damaged, including the library. No one got hurt, but many books were ruined. So students, teachers, and parents organized a book drive for the library.
People have been dropping off boxes of books all morning. Heavy boxes of all sizes are stacked up. Volunteers are ready to bring the books inside. But the boxes are really heavy. It's too far to push or drag the boxes. How will you get the books inside?
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 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. Everyone is working together now that they have the right tools. 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. Simple machines help us do work. They move things faster, farther, or more easily than we can without them.
axle
wheel
axle
Simple machines have no more than a few parts. Some have just one part. Nearly every machine contains one or more simple machines.
Think about a school bus. The door’s hinges are levers. The set of stairs you climb to get inside is a type of inclined plane. These are examples of simple machines.
You can find wheels and axles on wagons and bicycles.
Machines That Go Round
If an object turns in a circle, it's probably a simple machine called a wheel and axle. A wheel is a disc that turns round and round. An axle is a rod connected to the center of a wheel. They rotate together.
Imagine pulling a load of books without wheels. The books would scrape the ground. As you pull forward, the force of friction pulls in the opposite direction. Wheels roll. So, there is less friction. And it takes less effort to pull the books.