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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214 views

Can a human body actually experience large gravitational time dilation?

As sometimes depicted in science fiction, can a human actually experience a large gravitational time dilation? These depictions often show a human experiencing a large dilation (ex. 1 minute = 10 ...
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1answer
237 views

Physics of Sound and the middle ear?

Once sound waves reach the eardrum, ,the eardrum moves back and forth and transmits those waves/pulses to three bones that serve to transmit and amplify the pulses to another "drum" in the inner ear. ...
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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 ...
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172 views

How can cats survive a 32 floor fall? [closed]

There have been instances where cats fall from more than 30 stories high, yet escape alive! The record was a cat which fell 32 floors, yet only suffered only slight damage to its body and lost a ...
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1answer
56 views

What would the ideal amount of gravity be for an Olympic sprinter?

The goal here is to get the sprinter running as fast as possible. How much of an effect would more or less gravity have on the top speed of an Olympic sprinter, say... Usain Bolt? 6 ft 5 in (1.95m) ...
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1answer
1k views

Can humans hear transverse sound waves?

According to Wikipedia and validated by a clever thought experiment here, sound waves can be transverse as well as longitudinal, if they're propagating through a solid. Consider my mind blown and my ...
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2answers
76 views

What is the difference between the way the brain sends signals as opposed to how an electronic device sends signals? [closed]

As I understand it, a brain communicates through sending signals via ions and chemical reactions resulting in concentrations of ions, a computer sends signals by electrons. I'm really trying to do 3 ...
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215 views

What happens to your pulse rate when you are in zero gravity in space? [closed]

I am new to stack exchange, this is my first post. To start with, what happens to your blood pulse rate when you are in zero gravity? Does it increase or decrease? I thought a lot about this but am ...
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1answer
53 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
95 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
119 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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171 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? ...
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1answer
2k 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 ...
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1answer
250 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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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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218 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 ...
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2answers
610 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 ...
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1answer
214 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 ...
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2answers
368 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 ...
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1answer
179 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
5k 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
321 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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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
126 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 ...
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3answers
24k 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 ...
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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
316 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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2answers
166 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
360 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
744 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
141 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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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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617 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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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 ...
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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
378 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
83 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
526 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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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
92 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.
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1answer
608 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
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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
8k 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
98 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 ...
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1answer
626 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 ...