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26

It is all about the loss of energy during each stride - the tendons store some energy, but not a lot. A kangaroo and a greyhound, for example, have far more efficient elastic storage in their legs / tendons, allowing them to achieve (and maintain) greater speeds with less effort. Key phrase from the abstract in that reference: elastic storage of energy ...


6

Potentially yes it could. There are no noise-cancelling headphones to stop the U.S. Navy's 235-decibel pressure waves of unbearable pinging and metallic shrieking. At 200 Db, the vibrations can rupture your lungs, and above 210 Db, the lethal noise can bore straight through your brain until it hemorrhages that delicate tissue. If you're not deaf after ...


5

Looks like neutrons can cause visual perception: Visual phenomena noted by human subjects on exposure to neutrons of energies less than 25 million electron volts, Science. 1971 May 21;172(3985):868-70, "Six subjects reported multiple starlike flashes and short streaks on exposure to neutrons of energies up to 25 million electron volts. The probable mechanism ...


3

The RC circuit that approximates a myelinated fiber looks like a series of resistors along the length of the fiber with capacitors connected to ground at the gaps between the Schwann cells. The time to reach discharge voltage at the next junction after depolarization at the prior junctions will be determined by the time it takes to raise the capacitor ...


3

The second law of thermodynamics only applies to closed systems. The earth is an open system (as it is continually receiving energy from the sun), hence the 2nd law doesn't apply to evolution and increase in complexity does not violate any laws.


3

The universe is made up of one hundred billion galaxies each with between tens of millions of stars to hundreds of trillions of stars. So we have quite a few stars. It used to be somewhat unknown whether or not stars had planets and if so how many. Recently a satellite called Kepler was designed to look for evidence of planets and found that many stars have ...


2

I don't think it's clearly physics, but ... The same shape assumes your head or your hand or ... Circle (sphere) is the most efficient as regards the proportions of the "content" and the "skin". Any other shape requires more protective cover to hold the same amount of "content". And protecting the body from the outside world is the most important function ...


2

faster long-distance runners hit ~20 km/h (marathon records) while fastest cyclists can do ~40 km/h So what causes the difference? different cardiac activity? different power output during these activities? more energy loss for running? friction? impact of the bike gearing? something else? That is the main negative factor, than ...


2

This phenomenon is probably related to the cold shock response, a set of physiological changes that come about in response to rapid temperature change, such as that experienced by a human whose face is immersed in a cold fluid. The response is accompanied by respiratory changes, including an initial gasp (see here). It is related to the dive reflex. This ...


2

This article is very good in describing the dangers of electricity, which I suggest you read. http://www.allaboutcircuits.com/vol_1/chpt_3/4.html To summarise the article, $20\text{ mA}$ for $60\text{ Hz}$ causes "severe pain, difficulty breathing, loss of voluntary muscle control", whereas $20\text{ mA}$ for $10\text{ kHz}$ is in between "threshold of ...


2

Some kinds of mutation provide an example of this kind of indeterminacy. UV light can be bad for our health. One of the reasons is that, when we are exposed to sunlight, UVB photons are absorbed by double bonds in pyrimidines, which break open, become reactive, and dimerize (photo-dimerization). This damages the DNA in the same way that it would damage a ...


1

The repelling is another way of saying that owing to the strength of the hydrogen bonding between water molecules, the water molecules are better off with themselves alone as compared to with non-interacting non-polar molecules within. A substance dissolves only in a solvent, where the solvent-solute interaction is as strong (or stronger) than the ...


1

The fault in this reasoning comes from the fact that you are inspecting a small part of the system (the biosphere) and ignoring the total entropy in the system. All biological processes, from those present in bacteria (or for multicellular organisms, mitochondria) to firing of neurons in human brains, increase the total entropy of system.


1

If all you did was drink distilled water, it would not be terribly healthy for you. But most people eat as well - and that combination probably includes "healthy" minerals. Unless you binge-drink distilled water without any food, it's unlikely to cause serious health effects. Having said that - ions are pretty small - certainly smaller than 15 nm. But their ...


1

Schrödinger's work is known for two distinct ideas relating to the nature of living systems. The first is what he called "order from disorder," meaning the way in which organisms can maintain a low entropy (or high free energy) state by increasing the entropy of their environment. (I.e. by eating low-entropy food and excreting high-entropy waste). Although ...


1

Because work done to pull a pulley is less and the wind resistance is less while cycling than while walking because of the aerodynamic shape of the cycle. While cycling you are sitting and while walking you are standing which requires more energy. The friction between the tires and the ground is less than our legs and ground.


1

This would be perhaps better off as a comment, but my reputation says I can't yet comment. All the other answers get the physics aspect right, but there is more to it from the biology point of view which might help the total average: you can rest on a bicycle more effectively. You can rest (or at least save some energy) going downhill (while actually ...



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