Not only is this a beautiful demonstration of how much thrust can be generated by a fire hose, it also gives us a glimpse into what firemen might be doing while waiting around at the station when no one's looking. It's also a beautiful demonstration of the principles of rocket propulsion, Newton's third law, and the law of conservation of momentum.
First, let's calculate the approximate thrust generated by each fire hose. Because the hoses are able to accelerate the compact car off of the ground, the combined maximum thrust of the ten hoses must be somewhat greater than the weight of the car. Assuming that the car is on the lighter side -- say 2,000 pounds or so -- then each hose produces a thrust of at least 200 pounds. No wonder firemen have to brace themselves solidly in place when operating one of these babies.
First of all, let's set the record straight. Man is a natural long distance runner. Despite impressions to the contrary foisted on us daily from our predominantly sedentary and "well-fed" modern lifestyle, it is interesting to note that for long enough distances a well-trained human can outrun just about any other creature on the planet.
Of course, recognizing the health benefits of exercise, not all of us live a sedentary life, and running has become a popular form of physical activity. In addition to the exercise aspects, however, those of us with a competitive or goal-oriented nature, from the elite athlete to the recreational runner, might be interested in running faster. Obviously accomplishing a 5K personal best or qualifying for the Boston Marathon requires a solid training program and a substantial amount of hard work. But what about those incidentals that might enhance our ability to train and thus augment our performance on race day? (We're not talking about performance-enhancing drugs here.)
That's where the video comes in.
Now that's a neat little trick. Once again that characteristically Japanese sense of humor gives us an opportunity to glimpse some interesting physics in an entertaining venue. Of course we aren't too surprised to see a water skier plane over the water, or to see a rock skipping esthetically across a placid pond. However, a water slide entry propelling someone into an "unaided" skid across a swimming pool seems a more rare and special event -- even though the physical principles are the same.
The Academy Awards are nearly upon us, and this year we've got three films nominated in multiple Academy categories, each of which also fits the bill for our own PopSci Movie Science Awards. These distinguished nominees consist of the 2008 blockbusters The Dark Knight,Ironman, and Wall-E. Each of these movies, enveloped in their superhero/science fiction-esque and/or computer graphic wrappings, give those of us so inclined a springboard into discussing and analyzing a little bit of Hollywood science.
Here we have a fun and frustrating little game that exploits our engineering skills. How to build a stable bridge is what this game is all about. At each level of the game you're given a limited amount of imaginary cash with which to purchase your beams and supports. It's usually just enough to get the job done, if you do it right. Which isn't so easy.
In keeping with our movie physics theme of the past few weeks, it seems appropriate to take a look at the trailer from the action "science" disaster film The Core. As with Armageddon and its deadly asteroid, The Core starts with an interesting premise -- the possible disappearance of the Earth's magnetic field.
Heeding a suggestion from one of our readers, let's follow up on our discussion of artificial gravity. As we described last week, although the film Armageddon attempts to portray artificial gravity aboard a rotating space station, it does not take into account the fact that unless the radius of the station is very large compared to the height of a person, anyone on board will feel significantly different forces acting along the length of their bodies. The result: nausea, vomiting, dizziness, disorientation, and nothing similar to the sense of gravity as we experience it on Earth.
There are certain movies that wreak such havoc with the laws of the universe as we know them that, despite the risk of irate readers who only want to enjoy the fantasy, and despite the fact that they may not care about accurate science (after all "we all know it's just a movie), we have to deconstruct them anyway as a public service. Now Armageddon (along with The Core and The Day After Tomorrow) forms part of a "trifecta" of bad movie physics, and, although it's not a new release, it epitomizes its genre.
Here's a vivid example of an electrical short circuit in a beautiful natural setting. In brief, a short circuit occurs when the normal path of current is bypassed via an alternate route with very low resistance. Since current likes to take the path of least resistance, most of it will flow through the short circuit. Also, according to Ohm's Law (V = IR), reducing the resistance of the circuit will drive up the current. Large currents result in excessive resistive heating in circuits, and we usually want to avoid them.
The "Ruben's Tube" demonstration shown in the video gives a dramatic and visual representation of sound waves creating standing waves in a pipe. Whether or not you light the gas, once the speaker is on, there are sound waves traveling back and forth along the tube. Sound waves consist of alternating regions of high and low pressure. But by igniting the gas in the tube and allowing it to escape out of the holes cut into the top, we can see where the pressure is high and where it is low.