Rocket ties a string to a clothespin. "When I pull the string, the clip squeezes!" he cheers.
Raven follows the string with her finger. "What do you notice? Your hand is far from the clip."
Nova floats down the string. "A bike has a string like that too," she says. "Where might it go?"
Rocket grins. "From the lever to the brake!"
A rider squeezes the brake lever.
The lever pulls a cable.
The pull on the cable forces the pads against the rim.
The pads rub the spinning rim. Friction slows the wheel.
The brake that does this is called a caliper rim brake.
Friction depends on how hard two surfaces press together.
Press them together harder, and friction gets bigger.
So a firm squeeze on the lever makes more friction than a soft one.
Many bikes have two hand levers.
Often the right lever works the back brake.
Often the left lever works the front brake.
Some bikes are set up the other way. A grown-up can show you.
| Statement | True or false? |
|---|---|
| The lever pulls a cable. | ? |
| The cable pushes air into the tire. | ? |
| A firm squeeze makes more friction than a soft one. | ? |
| Pads press on the rim in a caliper rim brake. | ? |
Super tracking! Tomorrow we meet other kinds of brakes, including one you work with your feet.