Stack Exchange Network

Stack Exchange network consists of 174 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
Join us in building a kind, collaborative learning community via our updated Code of Conduct.

The tag has no usage guidance.

-1
votes
1answer
33 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
0answers
21 views

estimating number of electrons available for conduction [on hold]

I've been asked to estimate the number of electrons in a metal, and the number of electrons available for conduction. I don't want to use proper Fermi-Dirac or anything, I just want an easy way to ...
-1
votes
0answers
40 views

How loud is a jump in the water approximately? [closed]

I want to know, how loud the noise from jumping in water like high diving from a 10m springboard is.
-1
votes
1answer
45 views

Looking at Earth's history using a cosmic mirror [duplicate]

Assuming we have a very powerful telescope, and a huge mirror 1000 light years away from earth, is it possible to look at this mirror to see what people did on earth 2000 years ago? Is it even ...
1
vote
2answers
129 views

Bullet hits Earth at speed $0.99c$ [closed]

According to wikipedia, the speed of the neutrino is as close as we can get to the speed of light with an object with rest mass. As per the comments, since neutrinos come in different energies, let's ...
-4
votes
2answers
87 views

Would a thermonuclear explosion occur if an ICBM (without a nuclear warhead) was to land on top of a cylinder filled with liquid hydrogen? [on hold]

Would the impact of an ICBM landing directly on top of a metal cylinder filled with liquid hydrogen result in a thermonuclear explosion? Say this ICBM would be traveling at approximately 5000 mps/...
-3
votes
2answers
49 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 ...
-2
votes
1answer
53 views

What is the force behind this punch? [closed]

I originally asked this in worldbuilding due to the context, though I suppose it's just a physics question. I was never great at physics in school but let's say there's a super human and they're ...
0
votes
2answers
80 views

Effectiveness of cooling oneself by a hand fan

I recently had a discussion with a friend of mine regarding the effectiveness of handheld fans. My friend argued that you would always get warmer. I’m sure that this needn’t be the case, as the system ...
1
vote
1answer
28 views

How much stress do Elephants feel due to weight?

While we humans weigh around 70 kgs , Elephants weigh around 5000 kgs. My question is :While moving or standing ,how many more times than humans does the Elephant feel the stress due to weight? Is ...
0
votes
1answer
56 views

Collision Speed at which seatbelts become ineffective [closed]

In a car, what is the speed at which if you were to crash (eyeballs-out) your deceleration would be so high that your seat belt becomes ineffective and that you would've die whether or not you ...
16
votes
3answers
3k views

Does the Earth's rotation affect redshift measurements?

How do you account for the spin of the earth in the mechanical sense, when measuring redshift? Does the relatively slow speed of the earth have a major change in the measurement because of distance?
-1
votes
1answer
171 views

Why trains are not heavy? [closed]

I have seen a video on youtube where Feynman explains that engines of trains are heavy to compensate for the fact that steel has a low coefficient of friction. But, whereas this seems plausible for ...
1
vote
1answer
32 views

Whats the energy spent on a push-up? [closed]

Let a human of height 1.80 m, arm length of 0.5 m and weight 80 kg do a push up. How much energy did she spend? $$ F = m \cdot a $$ $$ E = F \cdot s $$ $$ \rightarrow E = m \cdot a \cdot s,$$ where $...
-2
votes
1answer
48 views

How loud would a sound have to be for it to travel the distance of Pittsburgh, Pennsylvania to New York, NY? [closed]

I'm just wondering if it's possible, more than anything. But if it is, how many decibels would the sound have to be to travel that far of a distance?
8
votes
2answers
2k views

How far can a shout travel?

I was wondering, if a person climbs a tower and shouts at the top of his lungs how much distance would the sound travel ? Would it reach someone 1km far? Assuming that there are no tall buildings in ...
35
votes
1answer
9k views

Can I eat myself into a black hole?

This was a humorous thought experiment that occurred while chatting about black holes. The person that I was talking to assumed that a black hole required a specific density to be achieved. I pointed ...
6
votes
3answers
164 views

Dam Son's problem: how long does it take to boil an ostrich egg?

The egg boiling problem is a seemingly simple problem posted from the blog of UChicago's physicist Dam Thanh Son. A chicken's egg has a length of 5 cm and takes 6 minutes to boil. An ostrich'...
0
votes
1answer
93 views

How loud is the sun? [duplicate]

The sun is a continuous explosion. The reason we cannot hear the sun is because of the vacuum separating us. If that space was to be filled with air, would the sun be audible?
-1
votes
2answers
50 views

How large of a capacitor is needed to hold 5,000,000,000 J? [closed]

Given today's technology, what size of capacitor (in farads and physical size) would be required to hold 5,000,000,000 J of energy, the estimate for the amount of energy in the average lightning bolt?
0
votes
4answers
111 views

How the Heisenberg principle holds for protons?

Does this principle holds for protons since their position is, in a manner of speaking, known and they are also assumed to be stationary at every popular physics book that I have read, including the ...
12
votes
4answers
2k views

What if the Chelyabinsk meteor had been a black hole of equivalent mass?

The Chelyabinsk meteor is estimated to have had a mass of 10,000 - 13,000 metric tons. A black hole of mass $13\times10^6\ \mathrm{kg}$ has a radius of $$ r = \frac{2GM}{c^2} = \frac{(2 \times 6....
0
votes
0answers
40 views

Can you destroy the Sun if you throw enough iron into it? [duplicate]

i have a vague understanding of how the inside of the sun works, but i remember from class that when the sun started "making" iron on it's core, it cannot go further; can't make a heavier element. ...
2
votes
1answer
40 views

Standard deviation and single errors of measures

During my courses of laboratory, we used as a rule of thumb the following statement: If you have less than five measurements (each of them with its error), the error of the mean is simply the squared ...
5
votes
4answers
183 views

What would happen to a 10 meter sphere of room temperature water if released into space?

Imagine that we had a space station with a relatively large hangar, and we allowed a ball of water to accumulate that had a 10 meter diameter and a water temperature of 20C. While the hangar is ...
9
votes
4answers
7k views

Can a 1 watt heating element boil water? [closed]

If I take a 1 watt heating element, put it in a glass of water and I put them both inside a sealed imaginary chamber that does not conduct heat outside (again, imaginary). Will the water eventually ...
0
votes
1answer
27 views

Estimating the viscous drag of a moving floating body

I am interested in the viscous drag of a floating body (let's say an cylindrical iceberg in water) moving with a constant velocity, s.t. the Reynolds number of the fluid is very large. I am taking a ...
13
votes
2answers
467 views

Should we take the elevator instead of the stairs to save energy?

In our university there's a posted sign that encourages students to take the stairs instead of the elevator to save the university electricity during the hot NYC summers. When you climb the stairs ...
0
votes
1answer
82 views

Why was the glass broken in the Lobby but not above the impact zone? - 9/11

Disclaimer: I do thoroughly believe that 9/11 was a terrorist attack, so please don't start arguing whether it was an attack or inside job, focus on the question. Also: I was about to post this in ...
-3
votes
1answer
54 views

Could enough people spin Earth backwards faster than they could run? [duplicate]

So, consider the theoretical situation in which the earth is no longer spinning, and we want to spin it up by running in the opposite direction (Yes, this question was inspired by the Nike commercial)....
6
votes
2answers
106 views

What would the sky look like if the Sun was a black hole?

As a complement of this Phys.SE question. What kind of lensing and diffractions effects from space would be perceived on earth?
0
votes
2answers
65 views

Linear or Quadratic Air Resistance

I'm trying to model a rocket's position with air resistance as a factor. The rocket is fairly low-powered (Estes A8-3, 9.7N of thrust for 0.7 seconds), and I estimate it won't be going faster than 50 ...
1
vote
0answers
23 views

What is the variance associated to the average gate fidelity?

Let $U$ be a unitary and $\mathcal E$ a map on a space of dimension $D$, and say we want to assess how "close" $U$ is to $\mathcal E$. A standard way to do this is using the average fidelity $\...
1
vote
2answers
44 views

If you are ontop of a giant heavy object that is falling from the sky, is it possible to jump and roll at the perfect time to survive? [duplicate]

I don't know if gravity or the speed of the drop would prevent us from jumping, but would something like this be possible? If it's not possible on the ground, is it possible in the ocean? I'm sorry ...
3
votes
1answer
89 views

Minimum size of a “water star”

So I had this weird idea the other day. We know that stars form from simple matter (dust, gasses, etc) forming a gravity well, attracting to each other, until the amount of mass and density in the ...
2
votes
3answers
76 views

How to calculate the Sun’s energy output? [closed]

What formula can be used to find the total energy being produced from the Sun in Joules per second? If I recall correctly, the energy is around $2.3012 {\cdot} {10}^{27}\,\frac{\mathrm{J}}{\mathrm{s}}...
0
votes
1answer
62 views

Could an object orbit a person's body? [duplicate]

Imagine you were on a spherical spacecraft that had equal mass all the way around and you were deep in space, away from the gravitational pull of any planetary bodies or stars. If you released a ...
3
votes
1answer
41 views

How much faster is the chain reaction in a power plant than that of natural uranium ore? What about a nuclear bomb?

How much faster does the fissile uranium in a power plant 'break down' than an equivalent amount of naturally decaying U-235? How much faster is the chain reaction in a bomb compared to a power plant?...
0
votes
1answer
31 views

Is the mean CBM frequency more red-shifted since discovered in the 1960's?

If the universe is uniformly expanding at rate x, is possible to measure that the CBM has increased its red-shift value over time? If the red-shift is a static value, is it possible that the ...
2
votes
1answer
120 views

Free fall time of collapsing non-rotating star in GR according to a distant observer

Suppose a star with a spherically symmetric mass distribution, mass $2\cdot M_{sun}$ and initial radius $R$, undergoes a gravitational collapse after all gas pressure has vanished. The final radius ...
5
votes
2answers
664 views

What if we throw many buckets of water into the Sun?

What will happen if we throw many buckets of water into the sun and keep repeating the process? Will it get cooler or hotter?
39
votes
4answers
7k views

What would happen if Jupiter collided with the Sun?

This question is inspired by a similar one asked on Quora. Let's say a wizard magicked Jupiter into the Sun, with or without high velocity. What happens? The Quora question has two completely opposed ...
1
vote
0answers
32 views

Which planets would be visible from the Saturn system using the Naked Eye?

I was wondering which planets would be visible using the Naked Eye from Saturn? Would these planets always be visible or disappear as they got further from Saturn? Plus which planets wouldn't visible ...
0
votes
2answers
98 views

Given $2\text{ °C}$ atmospheric temperature rise, what would be the temperature increase if confined to an oven?

Consider the 2 °C average global atmospheric temperature rise as discussed by the IPCC. Assume an oven with an the interior that is a perfect cube having a volume of one cubic meter, empty of ...
1
vote
1answer
32 views

How would I calculate the speed passengers 'jump' based on the speed and displacement of a plane during turbulence?

I read recently that if I'm in a plane that hits turbulence, the plane might only move 1 to 20ft. However, due to the speed that plane is travelling at (say cruising at 550mph). The passengers in the ...
2
votes
2answers
109 views

Do you create gravitational waves by clapping your hands?

I was thinking that given that GW's can be created by the merger of both black holes and neutron stars I don't see why any two colliding objects wouldn't also be able to create gravitational waves, ...
0
votes
1answer
84 views

How dangerous is a neutrino experiment near human habitation? [duplicate]

I just read about people trying to capture neutrinos and study them. America has a lab in Antarctica and France deep under the ocean. Is it dangerous to conduct such an experiment where people live or ...
1
vote
1answer
25 views

Human body water storage effects on weather patterns

There are 7.614 billion humans and counting. On average a human being consists of 60% water. With that water being locked away from natural circulation for an average of 80 years. Are there any ...
3
votes
2answers
233 views

Do you round uncertainties in intermediate calculations?

Let's say I have an experimental uncertainty of ±0.03134087786 and I perform many uncertainty calculations using this value. Should I round the uncertainty to 1 significant figure at this stage or ...
0
votes
5answers
103 views

Is it possible to harvest the energy from the movements of a satellite in orbit?

I was thinking about how energy is harvested on Earth from movements of certain forces like wind and ocean currents. Could similar principles be applied in space? Satellites are virtually in ...