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Bike Shop 3-5 / Week 07 / Wednesday
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Week 07 · Brakes

Wednesday

Many kinds of brakes
// Friction that stops the wheel
⏱ about 15 min

Wednesday: Many Kinds of Brakes

Raven brings in a small bike with no hand levers at all. Rocket scratches his head.

"No levers? How does it stop?" he asks.

Raven looks closely at the back wheel. "What do you notice about the middle of this wheel?"

Nova circles the pedals. "Try thinking about which way the pedals turn," she says. "Forward is not the only way."

Four kinds of brakes

KindHow it worksWhere the friction is
caliper rim brakelevers pull cables, pads press the rimon the rim
coaster brakepush the pedals backwardinside the back wheel hub
disc brakepads press a separate discon a disc at the hub
drum brakea pad presses inside a closed druminside the hub

A coaster brake works when the rider pushes the pedals backward.

Coaster brakes are found on some children's bikes and tricycles.

A disc brake has a disc fixed to the middle of the wheel.

The disc sits away from wheel spray, so it stays cleaner.

Drum brakes can get very hot. Some hubs carry a label: do not touch for a while.

NAME THAT BRAKE
  • Read the question.
  • Tap your answer.
Raven's bike has no hand levers. It stops when you pedal backward. What brake is it?
Which brake squeezes a separate disc near the hub?
Where is the friction in a caliper rim brake?
StatementTrue or false?
Every brake adds friction.?
A coaster brake works when you pedal forward.?
A disc brake sits away from wheel spray.?
A drum brake hub can get hot after braking.?
WHY THIS EXERCISEEvery kind of brake makes friction, just in different places.
Which way do you push the pedals to use a coaster brake?
WHY THIS EXERCISEA coaster brake works by reversing the motion of the pedals.
Try it
Look at a bike picture, or a family member's bike with their OK.
A grown-up holds the bike still.
Look for hand levers. Look at the middle of the back wheel.
Decide: rim brake, disc brake or coaster brake?
Safety first
Look only. Do not turn the pedals or spin a wheel.
Never touch a brake disc or hub right after a ride. It can be hot.
No bike? Sort the brakes in the table instead.
Bike I looked atHand levers? (yes or no)Kind of brake I think it has
bike 1
bike 2
RIM BRAKE, STEP BY STEP
  • ?The rider squeezes the lever.
  • ?The lever pulls the cable.
  • ?The pads press against the rim.
  • ?Friction slows the wheel.
  • ?The bike comes to a stop.
WHY THIS EXERCISEA rim brake turns a squeeze into friction on the rim.
In your Bike Shop Notebook, draw one kind of brake. Label where the friction happens.

Brake detective work! Tomorrow we test what water does to friction.

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