# Tag Info

61

We don't feel any acceleration because the Earth and all of us humans on it is in free fall around the Sun. We don't feel the centripetal acceleration any more than the astronauts on the ISS feel the acceleration of the ISS towards the Earth. This happens because of the way general relativity describes motion in gravitational field. The motion of a freely ...

49

John Rennie's answer is right from the viewpoint of General Relativity -- but since the question is tagged with Newtonian mechanics, it deserves a Newtonian answer too. In the Newtonian framework, I think the best answer to "why don't we experience this force" is that we can't feel forces that apply to our body at all. What we actually experience with our ...

12

According to the Equivalence Principle a free falling system cannot locally detect a gravitational field. However Earth is a large enough system such that non-local effects turn out to be appreciable. Solar tides are - although small - detectable. So in principle one can experience the Sun's gravitational field even though we are in free fall. What I claim ...

9

The Earth has a liquid outer core, a solid mantle exterior to that, and a solid core interior to it! So that’s how come the Earth has the heaviest, densest elements at its core, and how we know its outer core is a liquid layer. Like all elements, whether iron is solid, liquid, gas or “other” depends on both the pressure and temperature of the iron. Iron, ...

4

The Earth "compells" an aircraft to rotate with it through the fluid drag of its atmosphere. So a practical answer to your question is then "above the atmosphere", which is at about a $100{\rm km}$ height. This is the von Kármán line, which is often taken as the definition of the edge of space. The definition is made because at this height, a standard ...

4

If I understand correctly, you are asking if a meteor impact could (i) slow the Earth's rotation on its axis or revolution around the Sun enough to account for the 8 to 12-fold decrease in longevity of human-kind measured in Earth days/years; and (ii) cause 40 days of torrential rain, resulting in sufficient inland flooding to float a large wooden boat. An ...

4

Even if the orbit were a perfect circle, there's some acceleration towards the sun. If there weren't acceleration then the earth would move in a straight line (instead of a circle); but it doesn't move in a straight line therefore there's acceleration. In a sense, the earth doesn't feel the acceleration because it doesn't try to resist it: if you stand on ...

4

Do radio waves from the Sun reach Earth? Of course they do. It's just another form of electromagnetic radiation. If so, do they penetrate the atmosphere or are they reflected, absorbed, or scattered? That depends on frequency (or wavelength). The atmosphere reflects, absorbs, or scatters most incoming electromagnetic radiation. There's a window in ...

4

John Rennie has answered the question in terms on general relativity, but it can also be answered with Newtonian physics. Your question is very similar to this one: Why does the moon stay with the Earth? and I can refer you to my answer there. In short, the Sun isn't only pulling on the Earth itself, it's pulling on everything on it as well, including us, ...

3

This is a surprisingly simple thing to calculate. It is a well known result that a consequence of the inverse square law is that there is no force inside a symmetrical hollow shell. This means that as the object falls into the hole, it will appear to be attracted by a sphere of decreasing radius - the mass outside "doesn't count." The acceleration of ...

3

The Earth+windmill system has conserved angular momentum. When the windmill starts spinning the angular momentum of Earth must change in response. However this change is marginal. Furthermore the windmill system will stop spinning when the wind dies down and this will restore the original angular momentum of Earth (when I say Earth I mean everything inside ...

1

This is an interesting question and one that probably needs detailed simulation to settle. But one can make the following broad prediction: the shape of the meteorite would have minimal effect on the outcome, for the following reasons: At the kinds energies let slip in the moments of impact and the kinds of pressures and temperatures that prevail, all ...

1

Short answer: the changing composition between silicate-rich mantle and iron-rich core means the melting temperature does not increase sufficiently for the iron/nickel outer core to remain solid. The ability of something to solidify is a competition between the potential energy associated with the atoms that would occupy a solid lattice versus the thermal ...

1

Slight radioactivity inside the earth continues to produce heat - and given the size of the earth, this heat cannot easily get out. As a result, the deeper parts of the earth are very, very hot (think volcanoes) - and most phase diagrams will tell you that at sufficiently high temperatures, most things are liquid. Entropy favors it.

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Simple answers like "pressure keeps substances in solid state" are gross simplifications. If you look at any scientific source, a phase diagram often shows $p$ and $T$ (pressure and temperature) on the axes. This is because at different temperatures but at equal pressures, substances can have different states and vice versa for different pressures and ...

1

As soon as you get above the atmosphere (about 100 km off the surface of Earth, give or take), then there's nothing in particular that compels you to follow the Earth's rotation. Of course, once you get there, you will probably already be moving to some degree, depending on which mechanism you use to get yourself up. If you do, however, you can bring along ...

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Offhand I'm not sure where to find information about how much is absorbed, reflected and scattered, but the waves certainly do reach Earth, and some, at least, penetrate the atmosphere and end up in solar radio observatory detectors, otherwise we wouldn't have so many of them.

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You definitely don't need to use General Relativity to answer this question. It depends upon what you mean by "feel". If "feel" means "detectable by sophisticated instruments" then, yes, it can be "felt". But your body is not a very sophisticated detection instrument. According to what I've read elsewhere, the Earth speeds up by $1000$ $m/s$ as it moves ...

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