Grades K–2 · Machines
How do wheels help a wagon roll?
A wagon is easier to move when its wheels can turn. The wheels hold the wagon up while letting it travel across the ground. Their centers are joined to the wagon by an axle or another support that lets the wheels rotate.
When the wagon moves forward, each wheel turns. A new part of its round edge reaches the ground as the old part lifts away. The bottom of a rolling wheel does not have to scrape along the ground the way a flat box does.
The Push arrow points along the Level path. The wheels beneath the Wagon can turn, bringing new parts of each rim to the ground as the wagon moves.
In the diagramWhat helps a wagon roll?WagonLevel pathPushWheels can turnPush, turning wheels, rolling right.
A push to the right can therefore move the wagon to the right while its wheels turn. The wheels do not make the push by themselves. They change the way the wagon meets the ground.
Rolling still needs some effort. Wheel parts can rub, and a soft wheel or soft ground can change shape. If a wheel gets stuck and slides, much more rubbing can occur. Wheels help by allowing turning as the wagon moves.
About this explanation
Starting knowledge: Recognize a wheel and compare rolling with sliding.
Sources
- Next Generation Science Standards — K.Forces and Interactions: Pushes and Pulls — grade-placement context
- OpenStax — Simple Machines — adult background for rolling and ramps
- OpenStax — 11.1 Rolling Motion