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If your friend's energy+ yours= F1, then you would see your own energy expenditure halved, which we know cannot be the case. If your friend helps you push the object, then you are no longer applying the same force, or (lazy answer) the force is no longer localised and motivates the part of the object most subject to friction. So, once the object is first ...

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I'm sure everyone has had that concern when we encountered the definition for the first time, in school. There is a valid reason why this definition is still persisted with, despite the deficiency that you hit on. The most popular (and simple) forces in physics (also the ones with which we begin learning physics) are conservative forces, implying that the ...

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If you're pushing a 10-ton truck and it's not moving, you are not doing any work on the truck because the distance $ds=0$ and the nonzero force $F$ isn't enough for the product $F\cdot ds$ to be nonzero. Your muscles may get tired so you feel that you're "doing something" and "spending energy" but it's not the work done on truck. You're just burning the ...

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An electromagnetic field, in order to start being harmful to humans, would have to be strong enough to dictate ion motion in our nervous system, and electrical signals to and from the brain. After all, everything we experience is the result of electrical signals. I took 16 Tesla ( magnetic field units ) to levitate a frog. I would assume that's also probably ...

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I have a strong reason to believe I have found the correct answer to my own question, you may correct me if I'm wrong. But this image seems to explain everything about my question in one single hit: These are results from Bowmaker & Dartnall (1980). Relevant reference: Bowmaker, J.K., & Dartnall, H.J.A. Visual pigments of rods and cones in a human ...

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So the actual problem here is: Purple is the color at the very shortest wavelength we can see. Purple is an additive mix between what we see as red light and blue light. That just doesn't make any sense. I don't see how our brain can possibly perceive this as being the same color. Shouldn't both purple colors actually be different colors ...

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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 ...

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It's the same reason why simply holding the mass over your head uses energy, even though the mass is not moving. And the reason is the way your muscle tissue works, which is to continually contract and then relax - obviously with different parts of the same muscle firing off at different times.

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This is a responce to usumdelphini's comment: Is there a way to show this formally, without relying on experimental data? I'm not going to attempt a deep analysis of walking, but it's fairly straightforward to show that using your arm reduces twisting. Suppose you're looking down on the person walking from above, and suppose they're a cylinder $^1$. ...

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