Shortly before our crazy biker pulls the reverse-Knievel—jumping far past the landing area instead of far short—we hear one of his compatriots shout, “You can go twice as fast!” This is a faulty hypothesis, as it turns out, but to the layman it would seem to make sense. After all, our biker had previously executed a graceful flop straight into the giant pit o’ foam. Doubling the takeoff speed intuitively should double the distance he flies, putting him a little farther into the pit but still within its bounds. Right?
Not exactly. Though it’s impossible to tell from the video exactly how much faster the biker was going on the second attempt, any increase in speed would be liable to have unforeseen consequences. That’s because the best way to understand how the bike flies is not with the concept of speed, but with energy. Why? Energy, as the lab coats like to say, is always conserved—and it’s gotta go somewhere. In this case, all the energy the bike carries into the jump is used to lift the bike however many dozen feet into the air before gravity puts it back into the speed of the freefall.
The funny thing about energy, though, is that it increases with the square of speed. That means that an object going twice as fast has four times as much energy, one going three times as fast has nine times as much energy, and so on. And practically speaking, four times as much energy means our biker is going to fly four times as high and sail four times as far. Exponents, like landing distances, tend to increase quickly. It’s important to make sure your foam can accommodate them. —Michael Moyer
Web-video fans may have noticed the recent spate of clips featuring guys dropping Mentos into Diet Coke bottles. The resulting geysers make for hilarious, sticky fun and have been the subject of some scientific enquiry. Steve Spangler explains on his site that the explosions are caused not by a chemical reaction between Mentos and Diet Coke (so you can breathe easy about consuming the two together) but a physical one: Mentos are the right shape and weight to break the surface tension of the bottled soda. All the little bubbles that form around the candies create a gas pocket that forces the liquid through the small opening of a liter bottle, resulting in an explosive plume of pop. Read Spanglers page for a more detailed explanation.
The main objective of this blog post, however, is to draw your attention to the newest and best of the geyser videos—this one shot in Buckfield, Maine, where folks evidently have lots of free time on their hands. In it, two guys in lab coats (Fritz Grobe and Stephen Voltz, of eepybird.com) re-create the audio-synchronized fountains at the Bellagio in Las Vegas using Coke bottles and Mentos. Highly entertaining stuff, and it even has a cool soundtrack. —Megan Miller
Related:
The Rocket That Runs on Oreos
Sugar: Future Fuel?
