Physics Buzz

On this week's podcast , we used physics to get to the bottom of an old bicycling myth. A bike made out of aluminum isn't guaranteed to give you a rigid, rough ride, while a bike made of steel isn't always going to be smooth and compliant. The different metals have their own unique properties to be sure, but the design and engineering of a bike has much more to do with how it feels than just what it's made of.

A typical crank. Image: Hoangquan hientrang via wikimedia Investors beware, when something sounds too good to be true, it usually is. Right now an entrepreneur is asking for money to manufacture bicycle parts that he says will give cyclists more power, even though the way he claims it works is contradicted by the laws of physics. The cranks of a bicycle are what connect the pedals to the front gears. They're lever arms that cyclists exert a force onto the end of, through the pedals, in order to turn the front gears. The front gears pull the chain which then spins the rear wheel, sending the bike speeding along. Z-Torque cranks. Image from z-torque.com Just about all the cranks on the market are a straight line from the pedal to turning radius. However a company called Z-Torque claims that their cranks give cyclists more power just by changing the crank arms into a bent shape. The problem is that physics doesn't work like the company claims it does.

On this week's podcast , Calla and I found out how the bikes of yesteryear lost their enormous front wheel when they started using two gears connected by a chain. Gears let riders get the most out of pedaling. They redirect the force of the rider's stroke over a long stretch of road if they're trying to speed down the highway, or condensed into a small section of road if they're powering up a huge hill. What setting your bike is in is measured in " Gear Inches ." A gear setting that moves you really far with one single turn of the pedals is said to have a lot of gear inches, while a setting with only a few gear inches will only move you forward a little bit.

How many times do your bicycle wheels spin around on your way to school? Bonus question: Is this the same number of times your feet pedal around? This might be difficult to answer if walk to school or take a train. In either case just cycle your feet around and pretend you are riding a bike. If people look at you funny, just tell them it's a physics project. This excuse always works in any situation. For instance if you trip on the sidewalk and onlookers start laughing, just tell them you were testing Einstein's Theory of General Relativity. Suddenly they will be impressed.