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Questions tagged [estimation]

The tag has no usage guidance.

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4answers
60 views

How much energy is in a 75 kg human being? Including atomic and electrical (charge) [closed]

To calculate the energy in 75 kg of mass is easy with E = mc2. But, how to calculate how much charge are in all our atoms? It is, too, a gargantuan amount of energy.
1
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4answers
55 views

Bicycle Fuel equivalent on l/100km

Is there a way I can calculate the equivalent how much a Human powered bicycle consumes in the equivalent l/100 Km of Diesel fuel? And also can I calculate the same for Gasoline fuel? And for ...
11
votes
2answers
1k views

Do variations of the Earth's magnetic field affect gravitational acceleration at Earth's surface, and if yes, by how much?

The Earth's magnetic field varies with time over geological time scales (we have phenomena such as pole inversion). Can this affect the acceleration of gravity at Earth's surface? I would think that ...
1
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2answers
104 views

How big would a black hole have to be to absorb the Sun?

How big would a slow moving black hole have to be to absorb or otherwise destroy the Sun?
0
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1answer
43 views

Resistance in fluids

Is atmosphere depth important in reaching terminal velocity in terms of slowing down an object. For instance, if a meteor was dropped from height $h_1$, would it hit the ground with the same velocity ...
1
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2answers
34 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 ...
2
votes
2answers
58 views

What is the point of generalizing a more specific result to an order of magnitude?

In my textbook, an example wants me to find an estimate of the number of cells in a human brain. It gives the volume of the brain as $8 \times 10^{-3}\ \rm m^3$ which it then estimates further as $...
1
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2answers
142 views

Is it possible to have a planet entirely made out of liquid water?

Earth is mostly covered in oceans, but they only go a few kilometres deep. It's obviously not possible to have a planet the size of the earth to be made entirely out of water, because of the kind of ...
0
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2answers
56 views

How far can you pee on the moon vs. mars? [closed]

Let's suppose you are at Elon Musk's Future Mars colony and you drank too much beer, how far can you pee on Mars if you can pee one meter on earth? If the next day you get on the shuttle to the ...
1
vote
1answer
35 views

Is 1 lux unrealistically low for a cell phone camera flash?

I have a light source which is similar to a typical cell phone camera flash. Based on a measurement and some calculations, I estimated that its illuminance is about 1 lux, or close to twilight values ...
0
votes
2answers
61 views

Time for black body to cool to a given temperature

I'm trying to figure out the time required for a blackbody to cool assuming it only looses heat via radiation. I can estimate the mass, specific heat, surface area, emissivity, initial temperature, ...
-4
votes
1answer
60 views

Gamma Photons vs. Muons; Which is more expensive [closed]

Which one takes more energy to produce? I ask as I theorize that keeping the plasma in a fusion reactor is very expensive. Muons, while useful, are too short lived. Maybe... Keeping the plasma at ...
4
votes
1answer
44 views

How long for released dye to uniformly saturate the oceans?

Suppose a supertanker filled with purple dye breaks open at a particular point in the middle of the Pacific Ocean and spills an enormous volume of purple dye into the ocean all at once. Imagine that ...
0
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0answers
31 views

What formulas do I need to calculate the time it takes for a room with opened window to become the same temperature as outside?

I want to calculate how long I have to open my window to become the same temperature as outside. To make things more easy let’s assume there’s almost no wind helping the exchange of temperature.
0
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2answers
43 views

Calculation of Gravitational Collapse time

The answers to Gravitational collapse and free fall time (spherical, pressure-free) describe the calculation of collapse time for a gas. For the case of neutral hydrogen gas with number density $10^4$/...
0
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0answers
5 views

Calculate weight of a barbell via measurement of period of oscillations

I have seen some videos on YouTube about some people that use "fake weights" in the gym, declaring to be able to lift much more weight than what is actually on the barbell. However, I think it should ...
11
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3answers
3k views

How would a fast-moving atom interact with a body? [closed]

I found this question on Quora: https://www.quora.com/Can-you-theoretically-shoot-an-atom-fast-enough-to-kill-its-target I think the Quora answer is good but incomplete, and it got me wondering what ...
69
votes
13answers
21k views

If visible light has more energy than microwaves, why isn't visible light dangerous?

Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
2
votes
1answer
48 views

If I drive East, how much lighter am I than if I drive West?

I'm at the equator. Suppose I am driving at x kph, in the direction of the Earth's rotation (i.e. due East), I presume that the force my vehicle exerts on the ground is less than when I am stationary. ...
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2answers
91 views
0
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1answer
54 views

How to get the radius of Bohr from the uncertainty principle?

I would like to know how to get the following result: \begin{eqnarray} a_0=\frac{4\pi\varepsilon_0 \hbar^2}{\mu e^2} \end{eqnarray} from the beginning of the uncertainty of heisenberg. If possible, I ...
2
votes
2answers
169 views

I'm travelling near the speed of light. Do I need to brake before using a super-massive black hole to turn around?

I'm taking one of those new fusion drives for a trip to nearby supermassive black hole. At a comfortable 1 G, it'll take me about 7 months of proper time to accelerate to 95% the speed of light. I'm ...
22
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6answers
6k views

Why does shooting a handgun accelerate a bullet to deadly speed without injuring the gun user's hand?

Momentum is defined by the product of mass and velocity. Now a projectile out of a gun has to have high velocity to penetrate a human body, as its mass isn't significant. But to reach this velocity, ...
0
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2answers
77 views

Do comets and meteors attract artificial satellites while passing by?

What will be effect on artificial satellites when comets or meteors come close or pass by?
0
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1answer
39 views

Laser guns and scattering

I recently read an article that explained how the US Navy would like to use laser guns in the infrared region, with a high power - 500,000 W I guess. However, because of Rayleigh scattering that ...
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
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2answers
50 views

Is lift force proportional to size?

I'm trying to calculate lift force of a particular object I'm working with. However, I can't find much information on how much force is required for an object to stay in flight though. My questions ...
0
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1answer
37 views

Casimir effect - gravitational influence?

Regarding the Casimir effect, is gravitational attraction too weak in order to explain the attraction between the plates?
-4
votes
1answer
53 views

Is it possible to use an accelerator/collider as a space engine? [closed]

I was just trying to get a discussion going about physics that we can already create. I did not realize that I would have to write a paper to ask a simple question. Is it possible to use an ...
33
votes
6answers
8k views

What is the probability for an electron of an atom on Earth to lie outside the galaxy?

In this youtube video it is claimed that electrons orbit their atom's nucleus not in well-known fixed orbits, but within "clouds of probability", i.e., spaces around the nucleus where they can lie ...
-1
votes
1answer
97 views

Electric force is stronger than gravitational force yet gravitational forces holds the Sun and planets in their orbits around the Sun [closed]

The electric force between an electron and a proton, between two electrons, or between two protons is much stronger than the gravitational force between any of these pairs of particles. Yet even ...
0
votes
0answers
68 views

Approximate probability of a person's wavefunction collapsing to the moon?

As a sort of introductory concept to quantum mechanics, I've heard many explain that there's a small but nonzero probability of unlikely events happening: your hand quantum tunnels through the desk, ...
7
votes
2answers
1k views

How much energy is wasted by a noisy refrigerator?

I recently bought a new refrigerator for my kitchen. The feet are adjustable but I've been lazy. Whenever the motor runs and the feet aren't all touching the floor there is a loud buzzing noise. As ...
3
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2answers
46 views

High intensity laser and neutrino pair production

Given the very small rest mass of the neutrino, visible photons have plenty energy for neutrino pair creation. What would be the probability of $\gamma \to \nu + \bar\nu$? Would the neutrinos be ...
-5
votes
3answers
76 views

How much electricity can a kilo of electrons produce?

I know how stupid this question sounds. I heard my grandma say something close to it in a phrase "It's a 1000€ aircondition, it's not gonna consume 200 kilos of electricity !" Made total no sence ...
2
votes
1answer
16 views

Can we estimate the coefficient of friction between two objects/materials?

I remember reading that it was impossible to theoretically estimate the coefficient of friction between materials even if their structure was known. The book where I've read this was The Feynman ...
6
votes
2answers
196 views

Would a human die from high air pressure at the bottom of the Mariana trench if it wasn't under water?

I read an article recently about gelatinous fish that live deep underwater, and if they were brought up to the surface would 'melt' due to the lower pressure not supporting their bodies. This got me ...
0
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2answers
106 views

Calculating the force on a bike chain idler sprocket

I am trying to get a rough estimate of the force on an idler sprocket in a bike chain line, in order to get bearings robust enough for the task. Assuming a chain tension of 150 pounds and an idler ...
1
vote
1answer
31 views

How much clamping pressure would it take to hold up the weight of a human?

I don't know anything about physics. This question comes from an argument I had with a friend. Basically my question is this: Is it possible for a human to hold themselves up only by clamping their ...
2
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2answers
30 views

Why doesn't ionized air give you a current shock?

According to Tesla coil, the air gets ionized and why doesn't ionized air give current shock to a person standing in the ionized air?
17
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2answers
7k views

Uncertainty principle for a sitting person

If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths. What am I missing? Do ...
1
vote
1answer
86 views

What is the minimum time required to travel 1 light-year from Earth and turn back? [duplicate]

Suppose I have a very powerful and durable rocket that is able to reach speed of light minus $10^{-1000^{1000^{1000}}}$ in $10^{-1000^{1000^{1000}}}$ milliseconds. Very instant acceleration. I can ...
-1
votes
2answers
70 views

Can shining a laser pointer on an Ice Cube melt it?

I heard in videos that if you use a laser pointer (Green if I recall) and point it on a ice cube, that it would cause it to start melting, is that true?
3
votes
1answer
61 views

How much does NASCAR affect the rotation of the Earth? [duplicate]

Many of us will be familiar with XKCD 162: Angular Momentum, in which someone spins counterclockwise to slow down the rotation of the earth and make the night longer. The mass of an individual human ...
1
vote
1answer
38 views

What would happen to a person's body if they entered a black hole? [duplicate]

One of the premises of the classic sci-fi show Farscape is that a person could travel through black holes, I'm curious as to what exactly would happen to a person body if you were to enter a black ...
2
votes
1answer
59 views

What does the gravitational potential of the Milky Way do to the CMB?

We sit in a gravitational potential, so there should be a blue shift on the CMB light from the potential of the Milky Way. Is this blue shift dependent on direction? Is it being subtracted from the ...
1
vote
2answers
70 views

How fast do nuclei need to be traveling when colliding for them to break apart? [closed]

I don't mean fission or fusion reactions with uranium or such. I mean gold or lead or even hydrogen collisions, such as in these particle colliders or outer space, wherein the nuclei seem to touch, ...
1
vote
3answers
78 views

Can average acceleration be exactly determined from discrete points separated by equal time intervals? [duplicate]

I am using the American dialect of the English language. The following definitions distinguish my question from the similar, previously asked question: https://ahdictionary.com/word/search.html?q=...
0
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0answers
31 views

How cold does Something need to be for String Theory to be relevant?

I’ve often read casually that in order for modern string theory and other competing quantum gravity theories to be tested absolutely enormous temperatures (or rather energy densities) are required. ...
58
votes
11answers
18k views

Why don't solar panels contribute to global warming?

I've been wondering this for a while but I have not yet encountered an explanation. This is from my understanding of physics, which is by no means expert, so sorry for my crude explanation: Energy ...