Our topic: Fun on a summer drive, if you like science.
An emergency vehicle coming at you will display the wonderful Doppler shift. Pay attention to the wails in the siren’s tone, and how — at the moment the vehicle has reached its closest point to you — a double phenomenon suddenly kicks in. The siren’s tone decreases (its pitch abruptly lowers) and also the spacing between the warbles gets extended as if its batteries were wearing out.
Listen for both simultaneous effects. Reason: noise from a fast-approaching police car may strike your ear at 820 mph while the retreating vehicle’s warble arrives at only 690 mph. Proof that sound, unlike light, is not a constant.
While stopped at lights, check out the sky. Through sunglasses, white cloud fringes or sheets of thin cirrus near the sun often display vivid pinks, aquas, or purples. This is cloud iridescence and it’s food for the inquisitive mind.
Since cloud borders often contain rapidly evaporating water droplets of varying diameters, light passing through them travels disparate distances so that the crest of one wave can coincide with the trough of another, canceling out that light entirely. Removing a major color takes away part of the mix that makes a cloud white. The remaining waves concoct new colors not part of the usual rainbow spectrum — colors seen nowhere else in the universe.
On the ground, such destructive interference makes oily roadside puddles exhibit colorful swirls with psychedelic designs. It’s proof the light is a wave and not acting like a particle, since particles can’t interact in this way. Gazing out of the car, wave advocates momentarily get the last laugh.
When passing trucks, notice their gleamy bumpers. What’s happening when things gleam? Metals have outer electrons capable of absorbing and re-emitting bits of light, while their inner electrons are frozen in place with too little flexibility to vibrate and emit photons. Result: sunlight hitting metals are not absorbed, nor does the light pass through. Instead, the light’s reflected only from their outer electrons, making metals neither transparent nor dull, but something else: Gleamy.
Next stop, take another look up to see if you can spot the moon. During one week each month you’ll easily see it in the morning sky. It will never be full and will always be lit up on its left side. This is the waning moon, usually a half-moon or nearly so, the phase that lies in front of us as we together orbit the sun. Look its way and you’re facing forward as we hurtle through space. Cool stuff.
If you stop without the AC on, the car heats up. Two reasons. Human bodies each emit 96.8° of heat (not a misprint) — basically matching a 100-watt bulb. Secondly, window atoms have electrons that don’t get excited by visible light, so it passes through, aided by glass’ non-crystalline structure. But infrared and UV do interact with silicon dioxide electrons, forming resonances or excitations. Since the windshield absorbs or reflect those wavelengths, it’s a barrier that explains why the Sun’s UV can’t burn or tan you as you Drive. And why IR created inside remains trapped, heating things up.
Back on the highway, roll down the window and see all your loose papers get sucked out. This is Bernoulli’s principle. Your car’s motion produces rapidly moving air outside. Fast motion means low pressure, which creates enough of a vacuum to pull out the documents. Look through the rear-view mirror and watch them blow away.
A small price for cool car science.
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