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Questions tagged [biology]

Questions about biology are OFF TOPIC and should be asked on the Biology Stack Exchange. However, questions about biology in the context of physics (e.g., biophysics) can be on topic here if the primary concern is physics.

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1answer
50 views

I need an accurate physics formula to compare Calories or energy burnt/expelled when running up & down differing Sets of Stairs [closed]

I am researching for a paper on the differing energy required for users to run up and down differing Sets of Stairs. This is specifically for outdoor Sets of Stairs which can vary greatly in 1) Ave ...
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3answers
94 views

Accelerating at $\rm 1,000,000 \, m/s^2$ to $\rm 1 \, m/s$?

What would it look like if someone was accelerated at $\rm 1,000,000 \, m/s^2$ to $\rm 1 \, m/s$? Would they die? Would their body stay intact? My guess is that the answer might be more interesting if ...
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1answer
92 views

Why don't we take humanity and push it somewhere with lower entropy? [closed]

Entropy increases overtime, which will eventually lead to the heat death of the universe. Surely though, there is somewhere in the universe with lower entropy then where we are know, given that, ...
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2answers
75 views

Why do many animals die at the same time when lighting hits surroundings?

I have been reading about many cases in history of lighting striking and killing dozens even hundreds of animals, to be more specific quadruples, at the same time. Apparently this doesn't happen with ...
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1answer
112 views

Why don't birds fly at higher altitudes than they usually do? [closed]

We usually see birds flying at certain altitudes (not considered to be very very high) . My question is that why doesn't a bird keep flying higher and higher until we can't see it ANYMORE?
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2answers
152 views

What sound frequency can be heard the greatest distance by humans?

What sound frequency can be heard the greatest distance by humans? Assuming a pure tone, single frequency, same source SPL (dB) for each frequency, outdoors with no obstacles between source and ...
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1answer
121 views

Have scientists thought about these two questions? [closed]

I would like to know if our vision bends with the earth or if the earth truly is round. If I look through a strong enough telescope to see around the world, would I be able to see the back of my head? ...
1
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1answer
1k views

How may sound waves behave inside the human body?

in Vibroacoustic Therapy (VAT) sound is transferred to skin surface via transducers that are in direct contact with the skin. This means no energy loss to surrounding air. We are mostly using ...
0
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1answer
223 views

Which is the most toxic isotope of plutonium and what makes it toxic? [closed]

Some sources say plutonium is one of the most toxic substances known, while this challenge from Bernard Cohen to Ralph Nader challenges the toxicity. I heard that only one of its isotopes is toxic, I ...
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3answers
1k views

Why do we use decibels instead of just using intensity to measure how loud things are?

In my physics book, it says that in the human ear, the sensation of loudness is approximately logarithmic. And that the relative sound intensity is directly proportional to a logarithmic ratio ...
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0answers
213 views

Does Blue Light Really Have a Dark Side?

I was reading the following article on Wikipedia which discusses the dangers of blue light: Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from ...
2
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2answers
545 views

Does wearing a coat require your body to produce less heat?

Question: If you’re wearing coat on a cold day, does this require your body to produce less heat to keep you warm? How can we model this energy exchange? This question is inspired by the idea that ...
3
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1answer
197 views

Danger to Expose Eye to 10,000+ Lux of Ultraviolet Light

Is it dangerous to expose the human eye to 3,000 - 10,000+ lux of UV (ultra violet) light in the 380 - 400 nm wavelength? I understand anything below 400 nm is tech classified as UV/UVA radiation ...
5
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2answers
331 views

How can a mace penetrate armor better than a sword?

So, I'm trying to comprehend, just why are weapons like maces are so good at killing opponents through armors (full-plate), that sword edges can't even hope to dent. When I skimmed through google, I ...
1
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1answer
170 views

How does the Venus flytrap count? [closed]

What is the physical mechanism the Venus Flytrap exploits to time the interval between an electric signal and the following one?
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2answers
4k views

Why do humans drown in water?

If humans have a density of 985Kg/m^3, then why do humans drown as water has a density of 1000Kg/m^3.
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1answer
307 views

If light carries its energy in discrete packets, why don't we see a series of flashes when we look at things?

According to the photon model, light carries its energy in packets called quanta or photons. Why then don't we see a series of flashes when we look at things?
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2answers
1k views

Why is unit of pressure (psi) used to determine things like bite force of an animal?

Whether in tv documentaries or journals, whenever they talk about an animal's bite force, it's measured in PSI anytime imperial units are used (ex: National Geographic, NIH Journal). Many even seem to ...
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2answers
113 views

Does time reversal symmetry hold in systems that use the geometry (shape) of a molecule as an input parameter to determine a subsequent output? [closed]

Does time reversal symmetry hold in systems that use the geometry (shape) of a molecule as an input parameter to determine a subsequent output? A system such as a synapse of a neuron that responds to ...
45
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3answers
23k views

Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

I am not planning on staring into the sun during an eclipse or any other time. I have been reading about how no variety of regular sunglasses are safe enough to view the eclipse with. I'm not talking ...
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1answer
1k views

Why can I look at the sun with my sunglasses but not at the solar eclipse?

Is the problem with seeing an eclipse that you have a sudden change between penumbra and regular sun? If that's the case, why can I look to the sun with my sunglasses on but I can't do it in an ...
44
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6answers
9k views

Does pure yellow exist in variations we can't discern? [duplicate]

If you add red light (~440 THz) and green light (~560 THz), you get what we perceive as yellow light (~520 THz). But I assume what you really get is a mixed waveform that we perceive as yellow? ...
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3answers
306 views

How does the human ear guess the source of the sound?

Suppose a sound is produced behind you. You can easily tell that the sound came from behind. Our ear lobes face towards the front and hence traps the sound waves which come from the front. Yet, we ...
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1answer
140 views

Are quantum measurement of a system only occurring with human interaction?

In quantum physics, any functional interaction like measurement/observation forces particles down to a single state. Yet when plants do their photosynthesis it's been discovered that they actual ...
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1answer
328 views

How does “sgnl” work? [closed]

I visited many sites and did lots of Google search but I didn't get my answer. In this link I read the article about how Sgnl works. and here's some text: "Sgnl will generate vibration through its ...
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1answer
661 views

Why is the work done by someone pushing a cart not zero? [duplicate]

We know that when force is perpendicular to displacement, then the work done by it is zero. If this is true, then why do the vegetable vendor (who pushes the cart by applying perpendicular force) ...
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1answer
137 views

If Proxima Centauri is only 4.25 light years away, why is there no attempt at communication? [closed]

It is known that the Proxima Centauri star system is merely $\approx 4.25$ light years away from Earth. Moreover, an Earth-like planet has been discovered around Proxima B that is within the habitable ...
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3answers
1k views

If gamma radiation is harmful to humans, why isn't natural light fatal?

If gamma radiation (which is comprised of photons) is harmful to humans when in close proximity, then why do photons in natural light from the sun not mutate human DNA to the same extent? I know that ...
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1answer
586 views

Is a human thought merely energy that is changed from one form to another? [closed]

Einstein: "Energy cannot be created or destroyed, it can only be changed from one form to another." Is a human thought merely energy that is changed from one form to another?
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1answer
3k views

Why can our bodies bleed? [duplicate]

Human systolic pressure is 16 kPa and diastolic 11 kPa but Earth atmosphere pressure is 101.325 kPa. I don't understand why when we are hurt we bleed instead of air enter into our body. How can blood ...
21
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3answers
3k views

Why do different letters sound different?

If one sings the letter "A" and "M" at the same volume and pitch, the two letters are still differentiable. If both pitch and volume are the same however, shouldn't the sound be the exact same?
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1answer
295 views

experiencing vibration when in contact with my desk computer and a rubbing a friend's arm [closed]

I was with a friend sitting next to my desk computer, I put my hand on the computer and the other one on my friend who is in contact with the floor. The thing is that when I rub my hand on his arm we ...
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1answer
79 views

How do cone cells perceive the wavelength of light waves?

Everywhere I look on the internet, I find this answer: "Cone cells perceive light." But I would like a more fundamental explanation. How do cone cells perceive and differentiate between these ...
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4answers
495 views

Could a planet without a Sun sustain human life by internal heat?

If you have a planet without a Sun that has enough internal heat and has a thick upper atmosphere that traps most of the electromagnetic radiation I think that it would be warm enough to have water ...
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0answers
49 views

How much heat do we lose perspirating?

How can I calculate the heat my body loses from perspirating? For example, X Jouls per liter of sweat.
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1answer
81 views

How insects move opposite to gravity? [duplicate]

My question is very simple: How insects move opposite to gravity? please dont tell me that they have Sucks because my comment will be what about insects if move on smooth walls like glass.
5
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1answer
604 views

If you suspended your DNA like a rope in its 6ft full length, could you detect it if you waved your hand through it?

I asked this question on biology.stackexchange.com (https://biology.stackexchange.com/questions/58151/if-you-suspended-your-dna-like-a-rope-in-its-6ft-full-length-could-you-feel-it/), and it was ...
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1answer
29 views

What is a safe mass flow rate

In my machine class, the instructor said that if we use compressed air to clean metal of ourselves then we'll actually get hurt because the pressure is too high. I am wondering, What is considered a ...
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4answers
7k views

What force enables us to walk?

When we walk, we apply a force $F$ on the earth at an angle $\theta$ . Thus, by Newton's third law, $$ F_{\text{me, earth}}=-F_{\text{earth,me}}$$ Therefore, the earth exerts a reaction force on us, ...
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1answer
95 views

Why do we refer to life on Earth when we talk about life on other planets? [closed]

I have always had thoughts about extraterrestrial life and I wonder why researchers largely compare the conditions for existence of life to that on the Earth? Is it impossible that on a remote ...
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1answer
40 views

Can a short-sighted person see a target 'better' than someone with no impediment, if target is very close?

Can a short-sighted person with no corrective appliance see an object more clearly than a person with no impediment, if the object is at an optimal distance for them (i.e. closer than the unimpaired ...
2
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1answer
558 views

Physical explanation of seeing sparkles?

I know this might look more appropriate to ask this kind of question on the biology or medical stackexchange but since this kind of cross-science question I'll ask it here. Sometimes when sitting and ...
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2answers
183 views

Time dilation. Does time dilatation affect physiological processes?

In time dilation, does the "aging" referenced include biological/ physiological aging? for example, in the identical twin concept, is it possible for the twin who travels to space and back to have ...
20
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5answers
6k views

How is it possible for other animals to have better night vision than humans, who can detect individual photons?

According to the Wikipedia article on night vision, Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These ...
0
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1answer
225 views

Electric discharge through my knuckle

In some particular days, it seems that my car is somehow at a different potential from the ground. When I get out my car and I wear my sneakers (that I think are better insulators than other kind of ...
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2answers
109 views

Could someone explain the Forster Resonance Energy Transfer?

My understanding of it so far is rather messy, and I haven't found a good source yet that describes WHAT it is rather than just stating lots of equations! I have read a source that mentioned it having ...
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1answer
84 views

Is the temperature of the surface of our body same as that inside the body?

the surface of the body is always subjected to the atmospheric conditions and thus the temperature of the surface is eventually equal to the room temperature then what does the temperature shown by ...
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0answers
1k views

Why water heat capacity has minimum at body temperature?

Water heat capacity has the following plot: One can see it has minimum near 40 degrees of Celsius, i.e. close to human body and other warm blooded animals have. Is this just coincidence? UPDATE ...
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2answers
1k views

Are living organisms deterministic?

Are living organisms physically deterministic at any given time? Since it's all physics and chemistry, it leads me to believe they are.
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1answer
486 views

How could lightning have killed 322 reindeer at one time in Norway?

Lightning is supposed to have killed 322 reindeer within an area that's about 50-80 meters in diameter on a mountain plateau in Norway. Nearly the entire herd died. Sources: (1, 2, 3, 4) Image ...