Rolling along
Four wheels, a box, and a handle. That’s all a wagon is. But with a
wagon you can easily carry a couple of friends or a load of empty
bottles—or even give the dog a ride.
When you use a wagon, a simple machine called a wheel and axle is
helping you. You can see the wheels—the round parts that roll over the
ground. The axles are the rods that connect each pair of wheels. The
wheels and axles turn together.
Putting wheels and axles on something makes it easier to move. A wagon
without
The wheels and axles on a wagon turn smoothly when you push. You don’t
have to work very hard to make the wagon move.
wheels would drag over the ground. The scraping, or friction, of the box
on the ground would make it hard for you to pull the wagon. But wheels
on axles go rolling smoothly along. When wheels and axles are used, even
big loads can be moved without much friction.
Cars, trucks, and buses are some big machines that have wheel-and-axle
parts. Those parts work just like the wheels and axles on a wagon. The
only difference is that a car, truck, or bus has an engine that does the
pushing. When you use a wagon, you do the pushing or pulling.
