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Drag Forces

two bicycles
Hold the bars and flex the knees
Pedal quickly as I please.
The wheels spin and my heart races
Now I'm really going places.
I'm cycling!   Anon.

Used world wide as a convenient means of getting around one's village or town, the bicycle is light, narrow, easy to store, and provides an economical way of moving from place to place. It can quickly pay for itself in saved bus or train fares and is a great way of getting exercise to stay healthy. These attributes have not changed since the machine was first 'perfected' back in the nineteenth century.

However, some major improvements during the twentieth century have made the ride easier and more comfortable. These include pneumatic tires, derailleur gears and hand-operated cable-pull brakes. Now, a U.S. company has introduced a bike that offers less maintenance and greater safety than the conventional chain-driven bike by replacing the chain and derailleur with an internal drive shaft. It remains to be seen if this 'advancement' will prove popular with regular riders. In any case, the internal drive shaft mechanism will have little direct effect on the amount of effort needed to move the bike and its rider forward.

Newton's second law of motion tells us that the rate at which an object (like a bike and its rider) changes its velocity depends upon how much force is used and how much mass (inertia) the object has. So we know that to get started and to move faster the rider must exert sufficient force to turn the pedals and then turn them faster. But there are other factors at work. As the bicycle and its rider move along the road there is friction between the tires and the road surface as well as a drag force due to friction between the air and the exposed surfaces of the rider and bicycle. The drag forces can be the most importance source of resistance to the forward motion of the bike and its rider.

Stumper Questions:

1. Is the affect of drag force on the bike and rider greater at slow or high speeds?

2. What is a derailleur?

3. Bicycle designers work hard to make their bikes aerodynamically efficient. What strategies can a rider use to be more aerodynamic?


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