Rocket builds a cart with wooden wheels. He rolls it over the bumpy path. Clatter, clatter, bump!
"My teeth are rattling!" he laughs.
Raven looks at her bike wheel. "What do you notice about this wheel? It has thin rods and a soft tire."
Nova hovers near the wheel. "Look at what the tire is filled with," she says. "You cannot see it, but it is there."
A bike wheel has a hub in the middle.
Thin spokes run from the hub out to the rim.
The tire wraps around the rim.
Most bike tires are filled with air.
| Part | Where it is | Its job |
|---|---|---|
| hub | the center of the wheel | the middle the wheel turns around |
| spokes | from the hub to the rim | pull the rim toward the hub to make the wheel strong |
| rim | the metal ring | holds the tire |
| tire | around the rim | touches the ground, filled with air |
Here is a surprise. Spokes do not hold the wheel up by pushing.
Each spoke pulls the rim in toward the hub.
A single spoke is thin and easy to bend.
But you could not pull one apart with your hands.
All that pulling together makes the wheel strong.
A wheel with spokes can be as strong as a solid wheel, but much lighter.
| Statement | True or false? |
|---|---|
| Spokes pull the rim toward the hub. | ? |
| One spoke on its own is hard to bend. | ? |
| A spoked wheel can be lighter than a solid wheel. | ? |
| The hub is on the outside of the wheel. | ? |
Long ago, bike tires were made of leather, then solid rubber.
Riding on them was bumpy.
Tires filled with air gave a smoother, more comfortable ride.
Some bikes for small children still have solid tires.
Wonderful wheel work! Tomorrow we find out how air can hold up a whole bike.