Rocket drags a heavy box across the floor. It barely moves.
Raven puts the box on the wagon. Now it rolls along!
"What do you notice? Same box, new way," Raven says.
Nova hums softly. "Would you like a hint? Think about rubbing."
When two things rub, they slow each other down.
That rubbing force is called friction.
A box sliding on the floor rubs a lot.
That makes the box hard to move.
A wheel rolls instead of sliding.
Rolling makes less friction than sliding.
So a wheel and axle makes moving things easier.
That is why wagons, strollers and bikes have wheels.
| Sentence | True or false? |
|---|---|
| Rubbing makes things slow down. | ? |
| Sliding makes less friction than rolling. | ? |
| A wheel and axle helps things move more easily. | ? |
| Bikes have wheels so they can roll. | ? |
A doorknob is round, like a wheel.
The rod through the door is its axle.
Turn the knob, and the rod turns too.
A doorknob also works like a lever, as Builder's Lab explores.
You learned why wheels help. Nice thinking!
Tomorrow we look very closely at real wheels.