Not all wheels and axles are used for rolling. Think about a wrench. The circle you make by pulling on the handle is the wheel. The axle is where the head of the wrench grabs the bolt.

You use effort to turn the wrench handle with force. The key is that the circle you make is larger than the axle. This increases the force.

The same thing happens when you turn a doorknob. The knob is a wheel connected to a rod—the axle. The rod pulls on a latch that moves out of the doorframe. Now the door can open.

This increase in force comes with a price, and that price is distance. You turn the doorknob a longer distance than the rod turns.

That’s the thing about simple machines: There are always trade‑offs. The larger the wheel, the less force you have to apply. But you have to apply that force over a greater distance.

So, you trade distance for force. When it comes to doorknobs and wrenches, as well as faucets and screwdrivers, that’s not a bad trade!

Another fun way to enjoy wheels and axles is on a bicycle. A bike is loaded with wheels and axles. The wheels and pedals are examples.

Bikes also have toothed wheels called gears. A chain connects a gear around the pedals with one or more gears on the back wheel. When you pedal, the chain turns the rear axle, so the rear wheel turns, too. The wheel is much larger than the axle, so the wheel turns a lot farther and faster than the axle. So does the front wheel, which “goes along for the ride.”

Wheels and axles make work easier—and more fun! What other wheels and axles do you use each day?