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The elucidation of the structure of DNA began as an exercise in x-ray crystallography. If you shine a beam of x-rays through a crystal, it will act like a diffraction grating, and the points of constructive interference will show up as dark spots on photographic film. This had been used for decades to determine the structure of relatively simple molecules. A ...


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Any thoughts on the second question? Could laser damage the dna, or perhaps bones, which could result in some cell damage-cancer? How deep laser go? What I need to know about it?


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I will explain the basic idea. The ink that is in the skin is just metallic particles that on average have bigger size than the one the white cells can "fight" and remove from the system. Although the body recognizes the "alien" particles living in the skin and constantly fights them (and this is the reason the tattoo wears out) it is unable to remove big ...


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Lift Your Feet for Energy Efficiency! I'm late to the party here, but let me offer a distinctly different explanation. Think of walking as simply using your legs like pendulums. Due to the fact that your legs are close enough to the same length, you need raise one so it can more freely swing. Thus, you raise one foot to move it forward, taking advantage of ...


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I might not be interpreting your question correctly, but I feel that there is a component to your question that requires more than friction and work to understand: why Kendo practitioners, renowned for efficiency of action, shuffle their feet. I am not a Kendo practitioner myself, but from what I understand, the shuffling serves the same purpose as the ...


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All the answers point out the evolutionary advantage in rough terrains. A rough terrain means that a shuffler would continually meet obstructions in shuffling which would require enormous energy to shift by the feet, and much less in lifting the feet. As far as energy consumption goes one should compare in flat terrains, like deserts and ice. Ice skating ...


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Our ancestors evolved in rather rough terrain - it's a bit hard to shuffle through tall grass, mud, marshland, rocks, hills etc. and unless you have hooves it's rather more wear and tear on the feet. In geo-biological timescales pavement is a rather recent arrival. And then there's all that time our evolutionary branch spent in the trees. Snakes shuffle ...


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This is probably not so much of a physics question as a biological one. Shuffling might consume less energy depending on the roughness of the terrain etc. My intuition is that it would but I don't know how to show that. It also depends on your definition of shuffling either being dragging feet (great amount of friction) or barely lifting your feet ...


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I think that the friction involved in shuffling would be much more energy-consuming than the energy involved in lifting our feet. Would we would here now if our ancestors shuffled away from predators? You could easily test it: shuffle a given distance, then later walk it, and compare how tired you are.


1

There is no limit to the velocity that a person may travel. However, there is a limit to the acceleration that a person can handle. This is complicated as that maximum acceleration depends on how long the person is at that acceleration, how fast they got there, their muscular structure etc. The shorter time you have an acceleration the greater that ...


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http://www.launc.tased.edu.au/online/sciences/PhysSci/done/kinetics/wep/Work.htm The above link talks about WORK, ENERGY and POWER. Does this basic concept of physics applies all only to OBJECT and not to Human doing the work or applying power and using its own energy? Just confused here and I think I was wrong in linking with Human energy. If I pushed an ...


4

Assuming your question is about the concept of energy in physics: The muscle actually uses chemical energy. How this works in detail is not a physics but a biology question. The chemical reaction will create heat and cause your muscle to contract. Consequently, your body loses chemical energy, that's why you have to eat, drink and breath, to keep these ...


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You cannot "see" a flash if the eye receives no stimulus even though the brain is directly hit by a neutrino and it would be impossible to detect it because: 1) There is no receptor of this sort in the brain. 2) A neutrino has an extremely tiny mass. I can assure you that if the human body was capable of detecting an individual subatomic particle colliding ...


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The cross-section for neutrino interactions is energy dependent. For solar neutrinos at $\sim 0.4$ MeV, which would likely dominate any neutrinos likely to interact (the cosmic background neutrinos have way low energies) , the cross-sections are $\sigma \sim 10^{-48}$ m$^2$, for both leptonic processes (elastic scattering from electrons) and ...


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If you are that fast in detecting light, you are seeing cosmic ray muons. They are charged and leave an ionizing track in anything they cross and Cerenkov light. in liquid, and the eye is mainly liquid. They are the most numerous energetic particles arriving at sea level, with a flux of about 1 muon per square centimeter per minute. This can be ...


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This definitely is not a neutrino. Neutrinos are hard to detect because they are light, quick, and have no charge, making them usually pass through matter. We build giant machines to detect single neutrinos. The chances of this happening extremely low.


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It is proportional to its cross-sectional area. "Muscle strength depends on the number of fibers in a particular muscle. Hence the strength of a muscle is proportional to its cross-sectional area" source: Conceptual Physics by Paul G. Hewitt



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