May 31, 2005
Snap, Buckle, Pop: The Physics of Fast-Moving Plants
From The National Geographic:
Fleet-footed animals, such as gazelles and cheetahs, aren't the only livings things that rely on speed for their survival. The same is true for some plants and fungi. Consider the Venus flytrap, the poster child for carnivorous plants: Its jaw-like leaves can ensnare insects in an eye-blurring one-tenth of a second. Other plants employ similar lightning-quick movements, if not to hunt, than to spread their seeds, squirt pollen, or shake off predators. Plants don't have muscles. So how can some plants move so quickly?
Using the laws of physics, two scientists have detailed the mechanical design principles that govern these speedy plant moves. "To understand biology, it is always useful to come up with general principles as we have in this case," said Lakshminarayanan Mahadevan, a professor of applied mathematics and mechanics at Harvard University in Cambridge, Massachusetts. Mahadevan and his student, Jan Skotheim, report their findings in tomorrow's issue of the research journal Science.
More here.
Posted by Azra Raza at 06:28 AM | Permalink
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This fascinating article could have been more enlightening if it had illustrated with simple physics examples that how energy is supplied is important. The total energy supplied to a system can be supplied in many and varying ways. The point is contol. For example, imagine blowing up a balloon with say, air. The air is normally provided to the inside of the balloon at pressure modestly higher than atmospheric in controlled bursts or even constant but moderate pressure. But imagine what would happen if you were adding air to the tires of your car from a source operating at many thousands times the normal pressure. A small short sudden burst of air might blow up the tire in your face. Control would be lost, along with the tire and likely your life.
Imagine an internal 4 stroke combustion engine. As the piston moves down in a cylinder, the air fuel mixture is brought into the cylinder. On the next stroke up, that air fuel mixture is compressed. Then, at just the right instant past the compression stroke, a spark is provided which causes an explosion which forces the piston down, while on the final "exhaust" stroke, all the remaining gases are expelled from the cylinder and the process is completed. The "power" stroke is what turns the crankshaft and what ultimately turns the back wheels and provides mechanical energy to the automobile.
But what if the air fuel mixture explodes or partially explodes or spontaneously explodes prematurely before the proper beginning of the power stroke? Damage and decreases in power can result due to "pinging". Or, for example, suppose the air fuel mixture provided such a violent explosion that the piston simply melted rather than providing forces on the connecting rod and crankshaft? For example, suppose one sought to us nuclear fuel and have a direct nuclear explosion on the piston. No mechanical energy would be provided since the engine, car and occupants would all blow up. This is why nuclear submarines do not have "nuclear", engines, but ordinary steam engines, the heat of which is provided by nuclear fuel.
Another example is that of the diesel locomotive. The diesel engines do not drive the wheels directly, but run an electric generator, which, in turn, runs an electric motor, which runs the locomotive. This provides the control system to operate the locomotive.
Otto Warburg emphasized the importance of this in the human body. It is oxygen which provides the energy of the "highest" living forms, necessary to operate the many body functions of humans, but when oxygen is lost and only the energy of the lower living forms remains, cells switch over to the combustion of energy like the lowest living forms and become "dumb", lost to an organized system control. After time, cancer results.
Posted by: Winfield J. Abbe | Jun 1, 2005 7:07:44 AM
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