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