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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.

111
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17answers
212k views

How does mass leave the body when you lose weight?

When your body burns calories and you lose weight, obviously mass is leaving your body. In what form does it leave? In other words, what is the physical process by which the body loses weight when ...
75
votes
5answers
7k views

Why can we distinguish different pitches in a chord but not different hues of light?

In music, when two or more pitches are played together at the same time, they form a chord. If each pitch has a corresponding wave frequency (a pure, or fundamental, tone), the pitches played together ...
58
votes
6answers
9k views

How does light combine to make new colours?

In computer science, we reference colours using the RGB system and TVs have pixels which consist of groups of red, green and blue lines which turn on and off to create colours. But how does this work?...
54
votes
3answers
23k views

Why don't electric fish shock themselves?

Fish like electric eels and torpedoes have specially designed nerve cells that allow them to discharge hundreds of volts of electricity. Now, while pure water is usually nonconductive, the dissolved ...
45
votes
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 ...
44
votes
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? ...
41
votes
3answers
7k views

Can ants walk on liquid mercury? [closed]

I'm not a physicist, but I was wondering: Can ants walk on dense liquid like mercury and why?
28
votes
8answers
7k views

Why is there a size limitation on animals?

Why is there a size limitation on human/animal growth? Assuming the technology exists for man to grow to 200 feet high, it's pretty much a given that the stress on the skeletal structure and joints ...
26
votes
2answers
4k views

How do photons get into the eyes?

I hope you will understand me correctly because there are some things that I translated. It is known that we see the world around us thanks to photons that are reflected from the surfaces of objects, ...
24
votes
8answers
11k views

Is it possible to squat quicker than gravity?

It's definitely possible to propel your body using muscle to move towards the ground quicker than gravity. But is it possible to squat quicker than gravity? Assuming squatting from your knees and ...
24
votes
4answers
3k views

Could quantum mechanics be necessary to analyze some biology scenarios?

As an example, we could talk about a neuron cell in brain, with a size of $1 \mu m$ (=$10^{-6}$ m), being the distance between one neuron and next one in a synaptic connection of around 40 nm (=$40 \...
23
votes
6answers
11k views

Physics of how the cochlea isolates frequencies along its length?

Can anyone explain the separation of frequencies along the basilar membrane of the cochlea please? (equations would be nice) I understand it being related to the resistance caused by fluid in the ...
21
votes
6answers
3k views

Are human eyes the best possible camera?

I am not a physiologist, but whatever little I know about human eyes always makes me wonder by its details of optical subtleties. A question always comes to mind. Are human eyes the best possible ...
21
votes
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?
21
votes
9answers
4k views

Why can we cycle faster than we can run? [duplicate]

This seems obvious: faster long-distance runners hit ~20 km/h (marathon records) while fastest cyclists can do ~40 km/h (Tour de France stats). But on the physical/biological level this doesn't seem ...
20
votes
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 ...
20
votes
4answers
20k views

Why do whips hurt so much?

What exactly is the mechanism that makes a whip deliver such a strong impact? Elasticity, torque, or pressure? Just hitting something with a plank doesn't deal nearly as much damage. What's the ...
20
votes
6answers
21k views

Google interview riddle and scaling arguments

I am puzzled by a riddle to which I have been told the answer and I have loads of difficulties to believe in the result. The riddle goes as follows: "imagine you are shrunk to the size of a coin (...
19
votes
4answers
5k views

If we feel it's hotter when humidity increases, then why do we feel it's colder when inside water?

When the humidity in the air is high, we sweat more and feel it's hotter than when the humidity is lower. So why don't we feel it's hotter when we go inside water, where the water content is much ...
18
votes
7answers
17k views

How can a human eye focus on a screen directly in front of it? [closed]

I am asking this question here because I think the answer has something to do with the way light is bent as it's captured through the eye. I saw a show a while ago about tiny screens on contact ...
16
votes
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 ...
16
votes
2answers
64k views

Effects of a very large magnetic field on the human body

Ever since reading about the NHMFL I have always wondered about this and asked several people without getting a good satisfactory answer. My question is, considering the simplest case let's say a ...
15
votes
4answers
520 views

On what specific astronomical observations is the Fermi paradox based?

This is a question about the Fermi paradox, a topic that can attract a lot of opinions. However, the scope of this question is strictly limited to a specific factual topic, and I've edited it quite ...
14
votes
2answers
589 views

Implications of parity violation for molecular biology

In biology, the concept of parity emerges in the context of chiral molecules, where two molecules exist with the same structure but opposite parity. Interestingly, one enantiomer often strongly ...
12
votes
3answers
1k views

Humans have an average energy budget of $100$ Watts, but the power radiated from the body is $1000$ Watts?

On average a human consumes around $2000$ kilocalories per day. This converts to roughly $2000000$ calories / $86400$ seconds or around $100$ joules / second giving roughly $100$ watts. But if you ...
12
votes
3answers
15k views

Is it possible to kill a human with a powerful magnet?

I'm asking in terms of physics. Can powerful magnetic induction rearrange spins of my body in such way I will die? How? Or maybe it can rip all iron from me, which would make my blood cells useless? ...
12
votes
2answers
427 views

Silicon-based life [closed]

My question may not be suitable here, because it's more of astrobiology. Life as we know it is carbon based. Is life based on silicon possible? What would the conditions for habitability for silicon ...
11
votes
2answers
7k views

Why are smaller animals stronger than larger ones, when considered relative to their body weight?

I am interested in why many small animals such as ants can lift many times their own weight, yet we don't see any large animals capable of such a feat. It has been suggested to me that this is due to ...
9
votes
2answers
17k views

How many frames can human eye see? [closed]

What's the limitation of our eyes? Can we differentiate 60fps from 120fps? Are new 144hz monitors just a marketing trick? Couldn't find any proper journals or studies about the matter.
9
votes
2answers
2k views

Why is it hard to breathe when cycling against the wind?

Sometimes when I bicycle against hard wind, I find it difficult to breathe. Others I have discussed it with have also noticed this effect. A possible related phenomenon that I heard from an ...
8
votes
3answers
2k views

Most True to Life Physics & Biology Simulation Engine? [closed]

I'm a programmer. I code in C++, C#, HTML5, and PHP. There are many graphics engines I have at my disposal. The question is: Does there exist a graphics engine that is as true to our reality as ...
8
votes
2answers
10k views

How can an an ant lift 50 times its own weight and pull 30 times its weight?

According to many sites like this one, an ant can apparently lift 50 times its own weight and pull 30 times its weight. Is it true? Can it be proved using physics? Though most sites agree that an ...
8
votes
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 ...
8
votes
1answer
3k views

Would travelling at relativistic speeds have any impact on human biology?

If a person was sitting on a craft that has accelerated to near light speed speed from Earth (e.g. 99.999% of light speed) would there be any impact on his or her human biology due to relativistic ...
8
votes
2answers
3k views

How to distinguish female and male voices via Fourier analysis?

What makes one, without looking, be able to identify the gender of the talker as male or female? I mean if we Fourier analysed the voice of males and females, how the 2 spectrums are different which ...
8
votes
2answers
2k views

Sunflowers and radioactivity

I read yesterday that sunflowers were used and to cleanup radioactivity at Chernobyl and the Atomic Bomb sites in Japan and may be used as part of a campaign to clean up the Fukushima area. But my ...
8
votes
1answer
8k views

How much sky do we see at any one moment?

When we look at any particular point the sky, what percentage of the celestial sphere do we see? This question arises from the notion that on average there passes one meteor per hour overhead. So ...
6
votes
2answers
568 views

Is my tritium keychain emitting significant amounts of radiation?

I recently purchased a tritium keychain, composed of a small glass vial of tritium gas partially enclosed in a stainless steel fob. Here are the Amazon links so you can see a specific example: Link ...
6
votes
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.
6
votes
3answers
323 views

Why do cones require more light than rods?

The title says it. In our eyes, why do cones require more light than rods? Like is it because of the energy needed to change the state of the existing atoms, the molecules or what leads to the need of ...
5
votes
5answers
4k views

Is it really impossible for Bumblebees to fly?

According to some source or other (I forget which now) it is theoretically impossible for bumblebees to fly by virtue of their size/bulk/aerodynamic properties. Is this old adage apocraphyal or true? ...
5
votes
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 ...
5
votes
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 ...
5
votes
2answers
199 views

How does electrical energy develop by concentrating ions on one side of a biomembrane?

In biology there is a topic called oxidative phosphorylation. In the first step of this process substrates such as isocitrate is oxidised and the electrons are transferred to coenzymes NAD+ or FAD ...
5
votes
2answers
177 views

Why (infra-)red light is not used in diagnostics?

I noticed that human body conducts red visible light quite well. A hand placed over a powerful red lamp seems to be semi-transparent while over any other color it does not. Possibly the light ...
5
votes
6answers
22k views

Limit of human eye flicker perception?

I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from ...
5
votes
2answers
129 views

How is it possible to survive more than a few cm submerged underwater?

Suppose you hold your breath and dive a meter underwater. Assuming the surface area of the back of your body is approximately $1$ m$^2$, you have about $1$ tonne of weight above you. If you were out ...
5
votes
3answers
4k views

What is the minimum optical power detectable by human eye?

If one is in complete darkness, what is the minimum optical power that the eye can "see" (let's say in 500-600 nm range). I found that for 510 nm, 90 photons can be detected (http://en.wikipedia.org/...
5
votes
1answer
1k views

What is the minimum pressure difference for your ears to pop?

I'm assuming the answer to this largely varies from person to person. Assuming you could instantly change the pressure around your head by amount $\Delta p$, what is the minimum $\Delta p$ for your ...
5
votes
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 ...