Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
2answers
115 views

Are human beings radioactive?

I am reading "The greatest story ever told - so far" by Lawrence Krauss. He starts chapter 9, Decay and Rubble, telling how he was shocked when he realized that humans are radioactive. When I first ...
-5
votes
1answer
80 views

Can a projectile bullet kill? [closed]

Today, I was watching a movie, in which a person shot a gun in air. The bullet went high in sky, became stationary for a moment and dived back and killing a non-innocent person by hitting him in head ...
-1
votes
0answers
25 views

Safe amperage and voltage for humans [closed]

What are safe amperage and voltage for a human-being? Starting from what amperage and voltage can we feel? I want to make a trap for thief, but I do not want to injure him
1
vote
3answers
179 views

Can radio waves be harmful to us?

I was studying about Microwaves and their action on water molecules in heating up the food. This all is probably due to Microwaves have wavelength such that it can be absorbed by water molecules (am i ...
24
votes
4answers
2k 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 \...
0
votes
0answers
25 views

The rise of BCI

If EEG and MEG are measuring different aspects of neural oscillations, why can't we measure the combined signals as a whole, when we are doing the same for higher frequencies? Why did the us navy ...
1
vote
1answer
63 views

Why hot soup is tastier than cold soup? [closed]

My physics teacher recently asked me this question. Can anyone answer the question?
-3
votes
1answer
52 views

Where does my mass go when i lose weight? [duplicate]

Presuming conservation of mass to be true, mass has to go somewhere if i lose weight. Doing workout i burn my fat to do some work but then where does that fat go?
0
votes
1answer
42 views

Is there a correlation between aging and the increase of organisms entropy?

This question is a restatement of Death by entropy. Question: Does aging, as we understand it nowadays (shortening of telomeres etc.) goes hand in hand with the increase of entropy? If so and an ...
1
vote
2answers
35 views

Fastest hyperloop-like vehicle which a human could endure [closed]

I'm currently writing on a science-fiction novel where a transportation system like the hyperloop has been built. Now, I'm wondering how fast I can make this. Since the plot takes place on many ...
1
vote
2answers
176 views

Am I positively charged or negatively charged?

We often hear that the human body has a weak electrical charge. Is it a positive charge or negative charge? Or maybe different parts of me have different electrical charges? Or maybe there's a ...
1
vote
1answer
31 views

How do we hear harmonics and how does it affect audio fidelity?

First and foremost, do we hear a sound wave as a sum of all the individual harmonics, at the fundamental frequency, or do we hear all the associated harmonics above the fundamental frequency and ...
1
vote
1answer
88 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 ...
0
votes
2answers
55 views

What is the max amount of photons per second of the rods and cones in our eyes?

The title says it all. I just cannot find any information about this - I have tried for so long now. Therefore, I figured that I could reach out to some clever guys in this forum for help instead:) ...
0
votes
1answer
47 views

Cycling: The energy behind it

I'm developing a school project (I'm studying software engineering) and it's about a sharing bicycles company. We need to calculate the total amount of necessary energy to travel from one point to ...
0
votes
2answers
25 views

What is the advantage of stacking the electrocytes? Of having the stacks side by side?

Electric rays (genus Torpedo) can deliver electric shocks to stun their prey and to discourage predators. The voltage is produced by thin, wafer￾like cells called electrocytes, each of which acts as a ...
2
votes
5answers
83 views

In thermal spas the temperature of steam is about $50^{\circ}C$, but feels way hotter. Why?

So when you're in hot water and start to move or something the steam feels really hot even though I read its temperature is about 50 degrees Celsius in thermal spas. So why does it feel that warm?
0
votes
1answer
152 views

Why don't we see inverted image while wearing spectacles? [closed]

We know that the lens in our eyes forms an inverted image on retina and brain reverses it to give the correct image. But when one wears specs the image would get reversed twice so we should see things ...
73
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 ...
0
votes
2answers
118 views

Relationship between blood pressure and cross sectional area of blood vessel

What is the reason why blood pressure and a larger cross sectional area of blood vessel cause a lower blood pressure and vice versa? This question is related to another question I found here. The ...
0
votes
1answer
75 views

Why do we sweat on a hot and humid day but the clothes are able to dry?

I know that on a humid day,water vapour content is high in air and as a result evaporation of sweat is lesser and hence we feel hotter. What I am not able to get is, if water vapour content is high,...
5
votes
2answers
125 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 ...
3
votes
1answer
39 views

What forces the maximum speed of a cyclist on a steep climb?

I know that on a flat road drag is the main force, I have to provide as much force as the drag (and the friction in the drive train) produces. I can also see that the faster I ride, the harder it gets ...
2
votes
1answer
30 views

Experiments in ISS

Recently a Japanese capsule brought back proteins that were created in ISS in the absence of gravity. Researchers will study them to "understand their folding better". My question is, regarding ...
0
votes
1answer
77 views

What are the main causes for eyeball becoming too long or short in myopia and hyperopia? [closed]

myopia and hypeopia occur due to change in eye ball size or lack in cilliary muscle ability to accomodate. \n\n But why in lasik laser operation , the one's cornea shape is changed rather than acting ...
0
votes
2answers
48 views

Symptoms of lethal neutrino radiation in a hypothetical scenario

Core collapse supernovae release the majority of their energy in the form of neutrinos. According to an XKCD What If, the neutrino radiation alone from a supernova at a distance of just 2 AU would be ...
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 ...
1
vote
2answers
46 views

Does duration affect how lethal a current is?

It's been said in many places that it's not voltage that kills you but the source's current (or more so a combination of the two), but take a current of 0.1A which can be considered fatal. Would a 0....
1
vote
1answer
46 views

Do we have enough time for understanding space? [closed]

May be there more big bangs out there... while studding about space i some times think about a bacteria living on my body that may have a life span of 5 seconds if it has logical understating even ...
-3
votes
2answers
50 views

Energy that can control itself (A unit that can process information without body) [closed]

I read a book called The future of the mind. There it suggested a conscience that exists in the form of energy without body. Ideally, I thought the energy without body may take the form of light. ...
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 ...
-1
votes
2answers
46 views

Perception of curvature of human eye [closed]

How are human eyes able to detect the different curvatures of surface ? Basically how are the human eyes able to differentiate between a plane surface and a convex or a concave surface?
0
votes
2answers
114 views

Bernoulli's Effect on Blood Pressure [closed]

What is the impact of height, let's say being on top of a 4,000 m high mountain, on blood pressure / flow velocity given Bernoulli's Equation?
1
vote
1answer
111 views

What is the “comfortable” acceleration in a curve and braking in a car? [closed]

A car that makes a curve or a braking will naturally have its horizontal G-Force altered according to its speed and the intensity of the braking or the angle of the curve. My question is: which ...
0
votes
1answer
51 views

Would humans die of old age on an interstellar/intergalactic voyage? [duplicate]

It is often claimed that if we ever sent humans to colonize other stars, we would have to send them on generational ships. However, if the ship traveled at $99.9\cdots 9c$, wouldn't the passangers' ...
3
votes
2answers
83 views

Question about lenses in the human eye

To see near objects,the ciliary muscles contract and the suspensary ligaments loosen,making the lense thicker. İ don't understand how that helps us to see distant objects . To see distant objects ...
1
vote
2answers
44 views

Force, work and the apparent disappearance of Mechanical Energy [duplicate]

A man exerts force on a wall of bricks. The man must have consumed the energy he possessed (mechanical energy?) to exert the force. The man sweats and tires himself out but the wall does not move. ...
56
votes
6answers
8k 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?...
3
votes
2answers
260 views

Why might Roger Penrose argue that Godel's incompleteness theorem(s) suggest that consciousness is non-algorithmic?

This past March, when I called Penrose in Oxford, he explained that his interest in consciousness goes back to his discovery of Gödel’s incompleteness theorem while he was a graduate student at ...
3
votes
1answer
55 views

probability density distribution: From free diffusion to presence of a barrier

I am a biologist and I am not very comfortable with statistical mechanics. However, I want to learn and I am trying to understand. I just need some clues from people that handle these topics easily. ...
0
votes
2answers
27 views

What is the optimal light setting for human vision? In other words, is my vision better during the day or at night?

There seems to me to be two main effects that should be considered in answering this question. The first is that the iris dilates in low-light settings, which causes an increase in the numerical ...
-1
votes
1answer
808 views

How many calories in a block of wood?

I was recently thinking about the human body and the energy we get from food. I understand we don't have the ability to properly digest certain things like stones and wood and grass, but if we did, I ...
0
votes
1answer
77 views

Why universe is so perfectly made for us? [duplicate]

I am very eager to learn that, "Why universe is so perfectly made for us?" Or our universe is just stable by chance?
-1
votes
1answer
43 views

Same amount of calories burned for half the reps and double the weight? [duplicate]

So I was looking at the work= force x distance equation and was just wondering if for example I normally do 100 dead lifts at 100 pounds. Would I get the same calories burned if I did 50 dead lifts ...
4
votes
0answers
60 views

Has anyone ever actually considered a spherical cow? [closed]

Yes, I'm aware this question is somewhat whimsical. I'm sure every physicist is familiar with "Consider a Spherical cow". Has a cow (or any animal for that matter) ever been assumed spherical for ...
-3
votes
2answers
51 views

What if the luminosity of Sunlight increased by 10% [closed]

If the luminosity of sunlight increased by 10%, would people be able to survive outside? Would such brightness of light be very harmful to them, for exemple as much as the Mercury Vapour Lamp without ...
40
votes
3answers
6k 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?
-3
votes
1answer
120 views

Freeman Dyson: Advanced intelligences thinking in an expanding universe [closed]

I dont know if this is the correct place to ask this, because is highly speculative and maybe even hard scifi. But... I think is less speculative than the many worlds interpretation of QM or many ...
1
vote
2answers
319 views

Is the universe really “fine-tuned for life”?

I understand what is meant when we say the universe is "fine tuned", but I've seen it claimed it's is fine tuned "for life". Is it? When I look at known or even speculated life in our universe, I see ...
2
votes
3answers
77 views

What is the relationship between the amount of radioactive substance and the harm it does to the body?

This is probably a very simple question, but I wonder how the amount of radioactive substance is related to the radiation it emits and therefore the harm it does to the body. If I held 0.1g of barium-...