Hello, I'm Lou Bloomfield and welcome to how things work at the University of Virginia. Today's topic, wheels. [NOISE] Wheels are so common, and have been around so long that we simply take them for granted. Not only do we avoid reinventing them We avoid even thinking about them, but that may be a mistake. Their extreme commonness makes wheels more important, not less. And giving them a little attention may save you time, money and even misfortune. When they're used to propel a bicycle or car. Wheels serve as yet another simple machine. [SOUND] Without powered wheels, you'd have to imitate a cartoon character by churning your feet[SOUND] directly on the ground. But, wheels are far more than simple machines. They also save us from the limitations of friction. Without wheels nothing would just roll along. There would be no free-wheeling adventures and the wheels of industry would grind to a halt. In fact, wheels are so inextricably linked to friction that the story of wheels is also the story of friction. It's also the story of energy, but in a different way from ramps and seesaws. Ramps transformed energy from one form to another. Seesaws transferred energy from one person to another, but wheels prevent friction from wasting energy. That is, from grinding up useful energy into countless tiny, random fragments, that are then very difficult to use. We'll examine friction and wasted energy here in the context of wheels, and then use our new found understanding as we continue to look at how things work. At this point, let me have you think about a question. We won't actually ask this and answer it yet. But this is something you might have in your mind as we continue on through this episode. Suppose you're riding a bicycle or a car and you are stopped waiting for something. And then it's time to accelerate forward. Will you accelerate forward fastest if you twist your wheels so hard that they begin to skid across the ground, that is slide on the ground, or if you twist them somewhat less hard so that they just barely avoid skidding? To help guide us through the science of wheels we'll pursue six how and why questions. Why does a wagon need wheels? Why is sliding a box across the floor usually hardest at the start? How is energy wasted as a box skids to a stop? How do wheels help a wagon coast? How do powered wheels propel a bicycle or car forward? How is energy present in a wheel? There is one video sequence for each of those questions and a summary video at the end, but now on to the first question
