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1
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1answer
202 views

Continuity equation and pressure head in a tank

Consider a tank which is full of water. We connect a horozontal pipe at its bottom. When the pipe is open, water starts flowing through the pipe, then the velocity of water is proportional to the ...
2
votes
1answer
84 views

Why do flat sheets of paper twist more than paper cones as they fall?

If I cut a 10cm circle out of a piece of paper and drop it, it will twist as it falls, even if it's rigid. If I then cut out a one-quarter wedge of the circle and tape the remaining three-quarters ...
0
votes
0answers
20 views

Does the voltage of a spark depend on length and thickness of a spark across a gap? [closed]

Can the voltage that creates a spark be estimated by the length and thickness of the ark it creates across a gap? I made a zvs flyback driver with 2 IRFP250 MOSFET transistors running from 2.5 Amps ...
5
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2answers
149 views

Simple estimation of the critical temperature of water

I'm trying to develop fermi estimation skills and I came up with a question for which I don't even know where to start from. Here goes: Is it possible to estimate the critical temperature (say in ...
10
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3answers
5k views

Can superconducting magnets fly (or repel the earth's core)?

If a superconducting magnet and appropriate power supply had just enough $I\cdot s$ (current $\cdot$ length) so that when it was perpendicular to the earth's magnetic field, the force of the ...
4
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2answers
560 views

Ten-ping bowling: Can a ping pong ball knock over a bowling pin?

In this video we see a rather unorthodox bowling technique on display. The gentleman appears to knock over all of the pins using only a ping pong ball. It's a fake, of course: you could never knock ...
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1answer
2k views

Can I move an oil tanker?

Let's say that I'm standing at the edge of a basin made of concrete. This basin is filled with salt water and a ship floats on the water close to the edge of the basin. The ship is neither anchored ...
26
votes
3answers
3k views

How many X-rays does a light bulb emit?

I read somewhere that most things1 emits all kinds of radiation, just very few of some kinds. So that made me wondering whether there is a formula to calculate how many X-rays an 100W incandescent ...
2
votes
2answers
80 views

Reaction due to gravity

There is a reaction to the gravity of the earth on us but the earth does not move due to its huge mass. But what if I combine the weight of all humans and other things on Earth? Is it not enough to ...
1
vote
1answer
91 views

Reduction of Earth's Rotation due to increase in humidity

I came to know that, moon is moving away from earth, resulting reduction of Earth's rotation. Similarly, if Earth's humidity increases, water vapor will be move up to the air from water sources, will ...
4
votes
3answers
297 views

What was the amount of energy released in the 9/11 terrorist attacks?

I read somewhere on the internet that the amount of energy released by the terrorist attacks on the twin towers on 9/11 should have been of the order of 100 tons of TNT. This number surprised me, ...
-4
votes
1answer
74 views

Is the sum of mass of all planets in our solar system is 40% the mass of the Sun? [closed]

According to Chandrasekhar Limit,the mass of an object can not exceed than 1.4 times the mass of the sun.But according to some other theories,the sun was very large at former times and earth and ...
1
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2answers
215 views

7 Billion people jumping at once

What would happen if every person in the world gathered at a minimum possible area and jumped all at once? Would that have any effect on Earth?
2
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4answers
450 views

How long does it take for expanding space to double in size?

I have been reading about Hubble's constant and trying to make 'sense' of the theory of the expanding Universe. Is is possible that space in the universe expands uniformly? If so, absent of other ...
2
votes
3answers
131 views

How can I calculate whether a shelf is strong enough to support a falling cat?

I'm building some shelves for my cat to climb on. The highest position the cat will be is 2 meters above the next shelf. The cat has a mass of 6.5kg. The shelf has a maximum load of 20kg. Using ...
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votes
3answers
100 views

Is it possible to calculate the radius of star?

Suppose I know the Luminosity $L$, temperature $T$ and Mass $M$ of star. Assuming the star is very heavy so that we can treat it to be radiation-dominated star. This would imply that pressure inside ...
1
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0answers
17 views

Fermi's yield estimation of the Trinity Test [duplicate]

In Enrico Fermi's eyewitness account of the Trinity nuclear test in 1945, he gives a brief description of a method that he used to estimate the blast energy of the test: About 40 seconds after the ...
7
votes
3answers
796 views

Energy needed for Superman to take off and fly at the speed of sound

I just watched "Man of Steel", and I'm wondering if my logic is correct. Let's assume Superman is 80 kg. The energy required to take off from the rest to reach the speed of sound in air (if I neglect ...
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3answers
166 views

How do these factors affect the free fall of objects?

Take an example of two balls of different masses being dropped from about 250 meters from the ground. How do the following factors affect free fall: Air resistance. Absence of air resistance. ...
2
votes
1answer
172 views

Could one fire a bullet with sufficient speed to leave the Earth?

Consider a gun or rifle fired directly upwards. My original question was what speed would be required to escape the Earth. The escape velocity from the surface of the Earth is the classic $$v_e = ...
-4
votes
2answers
76 views

Would a piece of paper look as big as a small bedroom to an atom?, or bigger? [closed]

This evening my six year old asked me "Would a piece of paper look as big as this room to an atom?, or bigger?" ('this room' being a small sized bedroom) A friend suggested it would probably ...
1
vote
1answer
96 views

How many days it takes to travel to Cygnus? [duplicate]

BACKSTORY I read today newspaper and made discovery of planet Cygnus (in news paper of course :v) that human can live there! The distance is 1400 Lightyear. Assuming I travel with the world fastest ...
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2answers
144 views

How many atoms are there in our solar system?

Including all objects gravitationally bound to the Sun, how many atoms are there in our solar system?
10
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3answers
766 views

Can a building get taller at night?

UberFacts recently tweeted "Office buildings are taller at night—a 1,300-foot-tall skyscraper shrinks about 1.5 millimeters under the weight of 50,000 occupants." Is what they are saying valid? It ...
0
votes
1answer
73 views

Could a Jumbo Jet aircraft fly on paper wings?

My dad was an airline pilot and, during his training, his instructor told him that, in absolutely ideal conditions, (in practice obviously impossible) that the actual material composing the wing ...
18
votes
2answers
4k views

How big is a 1kW fire?

What is the size/scale of a wood fire that is producing 1kW? I'd like to improve my ability to conceptualize various power scales.
1
vote
1answer
607 views

How easily can the Earth flip?

The recent media attention to sunspot activity (however warranted) reminds me of a question I had long ago. Given the angular momentum and the slight 'wobble' of the earth, and remembering the ...
1
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2answers
56 views

Saturn V horizontally attached to Earth

If the Saturn V rocket were attached to the ground facing in the opposite direction of the Earth's spin, would it in anyway slow the Earth's spin on its axis? How significant of an impact would it ...
5
votes
3answers
1k views
1
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1answer
200 views

Effects of relativity on New Horizons spacecraft

How much would an atomic clock on board the new horizons spacecraft drift in comparison to an atomic clock on the surface of the earth near the equator after the spacecraft's 10 year journey to Pluto? ...
1
vote
2answers
44 views

What conditions would allow planetary-sized objects to collide and remain intact?

I am modeling some off-the-wall scenarios to try out with a game engine. One idea is trying to make a planet where some weird catastrophic incident has creates a funny shaped planet. I'm hoping to ...
2
votes
2answers
1k views

Temperature on the surface of the sun calculated with the Stefan-Boltzmann-rule

In a German Wikipedia page, the following calculation for the temperature on the surface of the Sun is made: $\sigma=5.67*10^{-8}\frac{W}{m^2K^4}$ (Stefan-Boltzmann constant) $S = 1367\frac{W}{m^2}$ ...
1
vote
2answers
733 views

Does body weight affect the speed when going downhill on a mountain bike?

We know heavier objects fall faster when dropped at certain height. I was wondering if I am going downhill on my mountain bike without any peddling, will I travel faster or slower because I am fat?
5
votes
1answer
101 views

Intuitively, why does removing solutes cost $k_B T$ of free energy per molecule?

I can calculate that if you want to, for example, desalinate water, you will have to pay a free energy cost of $k_B T$ for each ion you remove. In other words, removing an ion from a volume of water ...
2
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0answers
48 views

What's the fastest you can slingshot from one black hole to another? [closed]

Let's say you have your spaceship orbiting around a black hole. Its orbital velocity is arbitrarily close to the speed of light (or you can just set it to c*0.99 if it makes it easier.) There is ...
3
votes
1answer
86 views

Energy required to “glass” a given area of a temperate planet's surface

In some science fiction, orbital bombardment is portrayed as being able to vitrify the soil, or even the underlying bedrock, of a targeted area. While this is certainly not out of the question for ...
0
votes
1answer
52 views

Estimate the amount of atoms in the smallest speck of matter you can see with the naked eye [closed]

I am currently working through a physics text book at my own pace on Newtonian mechanics. I came across this question in the the chapter 1 problems and had a bit of trouble with it. My biggest issue ...
2
votes
3answers
390 views

Power to suspend a mass in air

How much power is needed to suspend a mass in the air? The four parts below deal with the same problem. I post them all here, should there be some subtle things I didn't see. The textbook problem A ...
0
votes
3answers
118 views

Is it possible for man to break Earth into 2 parts? [closed]

Many countries have extreme devastating nuclear weapons. Also they have weapons in very large numbers. I want to ask that Is it possible for man to break earth into 2 parts with the help ...
0
votes
1answer
116 views

Terminal velocity of a steel ball in water [closed]

I am investigating on the terminal velocity of steel balls moving in water. I used the balls with different diameters, such as 3.17mm, 6.02mm, etc. And I used a full-filled 1L graduated cylinder. I ...
3
votes
3answers
6k views

Which will stop first a heavier car or a lighter car?

If the friction from brakes, wind resistance and all such factors remain constant, which will stop first? A heavier car or a lighter car? How will the momentum of the car and gravitational pull on a ...
1
vote
1answer
35 views

How much energy is saved when using luggage with wheels? [closed]

How much energy is saved when using luggage with wheels as opposed to carrying the luggage? Thanks.
1
vote
0answers
46 views

Vehicle Driving off Cliff (Thelma and Louise movie)

What is the slowest speed at which a vehicle driven off a cliff can clear the cliff without catching its underside between the wheels? In the usual frictionless vacuum, this would appear to depend on ...
7
votes
1answer
136 views

Is it possible to remove the last block from a the lowest layer of a Jenga tower?

A while back, my brother and I had a discussion about the possibility of removing the last block from the lowest layer of a Jenga tower with the layer immediately above it having only one block in it ...
3
votes
1answer
114 views

Possible to make full loop on a swing only by “pumping legs”?

Is it possible to make a full $360^{\circ}$ loop on the type of swing in a children's playground if I power the swing only by "pumping" my legs? i.e. nobody pushes me?
1
vote
1answer
47 views

What is the acceleration due to Earth's rotational and orbital movements?

What are the accelerations due to earths spin and orbital motion around the sun? It must be negligible otherwise humans would have been feeling it, are there any instruments that can measure it? would ...
4
votes
3answers
248 views

What was the density of the universe when it was only the size of our solar system?

What was the density of the universe when it was only the size of our solar system? Did it approach neutron star density? Is it physically correct to even ask such a question?
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1answer
40 views

Calculating time dilation

I'm writing a science fiction story where the protagonist's experience requires long intervals between events. My plan is to put him/her/it on a spaceship between events at an appreciable percentage ...
1
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1answer
211 views

How many electrons are there in the universe?

Someone on io9 estimated there were about 10^80 electrons in the universe, but I want to ask the Stack Exchange physics community.
0
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0answers
41 views

Determine the amount of energy used for baking a cake

Let's suppose we have a room of temperature $T_0$ with an oven of volume $V$, both filled with air of density $\rho$ and specific heat $c$. We need to bake a cake in the temperature $T_1$. Thus we ...