Design Project
Motorized Vehicles!
Bicycles
 How many of you ride a bicycle that
allows you to change gears?
 How do you use the gears when riding a
bicycle?
 What do gears do on a bicycle?
Terminology
 Gear: we will use this term to refer to an
individual gear
 Sprocket: a gear that is connected to another
gear with a chain
 Pedal Sprockets: Sprockets connected to the
pedal crank
 Wheel Sprocket: sprockets on the rear hub
 Derailleur: mechanism that moves a chain
Gear and Gear
Combinations
 Bicycles are often identified by the number of
gears or speeds they have
 A ten speed bicycle has 2 sprockets on the
pedal crank and 5 sprockets on the rear wheel
hub which allows for 10 different combinations!
 Mountain bikes have 3 pedal sprockets and 7
rear wheel sprockets which allows for 21
different combinations!
Things to Consider!
 How is the motion of the pedal
transferred to the rear wheel?
 The pedal sprocket drives the chain,
which turns the wheel sprockets; both
turn in the same direction
What sprocket combination
would you use to go as fast
as possible?
 The largest pedal sprocket with the
smallest wheel sprocket
Why don’t we use this
sprocket combination all the
time?
 It takes a lot of force to get this
combination going
What sprocket combination
would you use to go up a
steep hill?
 The smallest pedal sprocket with the
largest wheel sprocket (low gear)
Why don’t we use this
sprocket combination all the
time?
 The bicycle doesn’t move very far with
each pedal rotation
 The sprocket combination easiest to
pedal is…….
 The sprocket combination hardest to
pedal is…….
WHAT DO GEARS DO!
 Gear allow the rider to change the
number of times the rear wheel rotates
for each pedal rotation
 This affects the distance the bicycle
travels with each pedal rotation
 Gears also allow the rider to change the
force with which the rear wheel turns