Why should a wheel have teeth? Wheels don't eat! But some wheels use teeth to get a lot of work done---and they can do things that other wheels can't do. > A wheel with teeth is called a gear....
What am I?
The answers to all of these riddles are wheel-and-axle machines. Can you find two that roll and two that turn? \_ > 1\. My axles are two, but my wheels are three. Even little kids ride > on me. > >...
Turn, turn, turn
How many wheels do you use in a day? You can count wheels that roll---bicycle wheels, car wheels, and bus wheels, too. They help you get places. A push from you or an engine makes the axle turn. And...
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...
How do brakes work?
> This bicycle has hand brakes---one for the front wheel and one for the > rear wheel. To stop, the rider squeezes the levers on the handle bars. Slow down! There's a busy street ahead. Stop your...
THE BIG WHEEL OF VIENNA
Once, an Englishman wanted to build a big Ferris wheel as high as a twenty-storied building. He wanted it placed in a park called the Prater in Vienna, Austria. Safety engineers checked the plans...
JUST FOR FUN
What kind of place do you think is most fun? A place where you can ride a giant Ferris wheel? Or a place where you can ride in a boat down a jungle river? Or a place that makes you feel like a giant?...
Plants that can swim!
Chlamydomonas Chlamydomonas is a tiny plant that swims like an animal! > Sometimes, 16 of these tiny plants form a jellylike wheel and live in > it together. If you peeked at a drop of pond...