Hot answers tagged

96

There's a lot of detail you could go into with regard to this question, as is done in the other answers and comments, but I think the answer itself is pretty simple. Imagine a surface that just barely surrounds your body, as if you shrink-wrapped a body in plastic. By the law of conservation of mass (valid in non-relativistic physics), the only way your body ...


67

Suppose current entering into this parallel circuit is $10A$ then almost all the current flows through poor small fish's body current through poor small fish's body = $10A \times \frac{1M}{1M+1} \approx 10A $ This is probably the large picture but I am just guessing. Hope its correct.


51

Essentially, losing of weight occurs by means of burning fuels precisely like your car does when it burns petrol and emits exhaust gases. The only difference is that for humans that fuel is to be found in the form of sugars. The fat is what you want to get ultimately rid off, of course, but sugars are more easily processed and so this is what you are ...


41

When you exercise, you "burn" more glucose, the simplified reaction for which (from Wikipedia) is: ${\rm C_6H_{12}O_6 + 6~O_2 → 6~CO_2 + 6~H_2O}$ So when you exhale, the carbon in the carbon dioxide, and the hydrogen and the oxygen in the water vapor, came from the glucose being burned, thereby removing that mass from the body.


39

I checked to make sure: The simple answer is that electric eels insulate their critical tissues with a layer of fat below the skin, preventing the shock from traveling through their body as the "path of least resistance". I may update with visuals and details if I can find good ones.


39

The following fact lies at the heart of this and many similar issues with sizes of things: Not all physical quantities scale with the same power of linear size. Some quantities, like mass, go as the cube of your scaling - double every dimension of an animal, and it will weigh eight times as much. Other quantities only go as the square of the scaling. ...


38

You feel cold when heat is flowing from you to the surroundings, your body tries to burn more energy to keep up your temperature, so you shiver. Water conducts heat much more effectively than air (more than 100x as well) so even with water at the same temperature as air you will lose a lot more heat and feel cold. When your body is too hot it losses energy ...


35

This question is sort of difficult to answer in an objective way, because it depends very strongly on your definition of "best." Natural selection favors traits which provide a reproductive advantage; no more, no less. Could our eyes be better by the standards of modern optical design, in terms of precision and features? Sure. I could easily design a camera ...


30

As others have pointed out, in metabolism you breathe in oxygen and exhale carbon dioxide with the net reaction being $$CH_2O + O_2 \to CO_2 + H_2O$$ The carbon dioxide gets exhaled, and the water is lost through some combination of other things. Let's think about whether this is a reasonable way to explain weight loss. A breath is maybe one liter of ...


28

Assume also that I have access to an immense amount of parallel computing processing power (I do). Unless you are an important person in the Chinese computational science world (using Tianhe-2), or you have access to secret government computers us mere mortals don't know exist (so they don't appear in rankings of the best supercomputers in the world), I ...


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 ...


13

No it's an urban myth. It's impossible for them to fly using a very simple and inappropriate model of wing behaviour - possibly closer to say that bumble bees can't glide like albatrosses


13

[Updated to correct a couple of mistakes pointed out in comments. Thanks!] At my age, it's clear that there's room for at least one major improvement: more accommodation. Accommodation, in this context, means the ability of the eye to focus at different distances. This is accomplished by changing the shape, and hence the focal length, of the lens. The lens ...


13

This is a common misconception -- evolution has not stopped a million years ago leaving all the creatures in the "best possible state"; it is a continuous pursuit of adapting to the current environmental conditions, with only aim in reproductive success. Moreover most of the population stays in even more suboptimal surroundings due to random mutations (the ...


13

Yes, it's very much physics related: The perceived smallness of distant objects is a direct function of how many space dimensions we live in. Here's an example: For a one-dimensional or "string land" creature, what would be the apparent difference in size between a dot nearby and a dot many miles away? If you think about it a bit, the answer is "none" -- ...


13

Different parts of the eye have different response speed. The corner of your eye doesn't see color, but is fast; the center sees color, and is slower. This means that when you look at a 60 Hz monitor straight-on, the image is perfectly steady; but when you look at it from the corner of your eye, it is flickering. As you go to even higher frequencies of ...


12

This is an example of "scaling laws". Have a look at http://hep.ucsb.edu/courses/ph6b_99/0111299sci-scaling.html - for once Wikipedia doesn't have a good article on the subject. The strength of a muscle is roughly proportional to the area of a cross section through the muscle, so strength is roughly proportional to size squared. That's why I'm a lot ...


11

Moving at a constant velocity, no matter how close to the speed of light, has absolutely no effect on the person moving. In fact, it has no effect on the laws of physics. This is the fundamental tenet of special relativity - you cannot tell absolute motion, only relative motion between different things. The changes you are referring to are what someone ...


10

It may have something to do with the growth rate of sunflowers. During peak growing times sunflowers can grow inches in a single day, which likely results in them drawing more water out of the ground, allowing them to concentrate the radioactive materials through deposition in the plant matter at a faster rate than other plant organisms. I would suspect ...


10

You can grow arbitrarily large as long as you are essentially flat. For example, one fungus covers several thousand acres; there's a grove of clonal aspen trees that may have higher mass. Scaling in three dimensions is much harder, though. The pressure on the bottom is proportional to the height--eventually that pressure is too great for tissue to ...


9

This has been extensively studied in linguistics and acoustics. Humans and other primates predict speaker gender through a combination of fundamental frequency $F_0$ ("pitch") and Vocal-Tract-Length estimates ($VTL$) which are a proxy for body size. Sometimes "formant dispersion" is used for $VTL$. It is usually defined as ...


9

Strength Strength goes like area. Intuitively, the cross sectional area of a muscle counts the number of muscle fibers (actually, myofibrils). Thus, $S\propto A \propto L^2$. But mass goes like volume, $M\propto V\propto L^3$. Therefore strength is proportional to the $2/3$ power of mass, $$S\propto M^{2/3}.$$ This equation expresses the fact that an ...


9

I'm only going to try to address the question of DC fields. Medical MRI uses uniform fields of about 0.5 to 3.0 T. In a head MRI, the Lorentz force on ions in the brain can cause neurological effects such as vertigo. I've heard that this shows up in particular when the patient moves his head. Here is a famous picture of a frog being levitated by a 16 T ...


9

There are two primary factors that allow the cochlea to isolate frequencies. These are generally referred to as passive and active properties: tl;dr version: The passive properties are due to the mechnical properties of one of the membranes in the cochlea, the basilar membrane, primarily the width and stiffness at a given point. The active properties are ...


8

Insect flight is different than bird flight. With insects, the rapidly moving wings, which do a figure 8 sort of motion, generates a vortex tube over the wings. This vortex by Bernoulli principle has less pressure, which permits the larger air pressure underneath to lift the animal up. If one is trying to understand insect flight according to the mechanics ...


8

According to this article: Different animals have different fields of view, depending on the placement of the eyes. Humans have an almost 180-degree forward-facing horizontal field of view, while some birds have a complete or nearly-complete 360-degree field of view. In addition, the vertical range of the field of view in humans is typically ...


7

One simple approximation that you could make is to assume that the human body is made of water. Then you can reduce your question to: what happens to water molecules in a magnetic field. Consequently, you would have to ask how you can break the Van der Waals Bond in water with a magnetic field. I think here you would have to differentiate between a static ...


7

This is obviously a very broad question, but here are a few thoughts that may be helpful. As dmckee points out in a comment, it's difficult to define consciousness. However, consciousness clearly requires computation, and computation is something that physics can address. There is a psychological arrow of time: we can remember the past but not the future. ...



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