I am a high school student. I read in my book that moon and satellite are in free fall condition with Earth. I asked my teachers about this, but I'm not able to understand. Can anyone explain to me why this happens?   Edit- if something is orbiting around the planet is he also in a free fall condition,.
5464
Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
15882
As a physics newbie I'm trying to get a grip on basic orbital mechanics. I think I'm beginning to get grasp on how bodies interact with each other. When a body approaches another body it accelerates due to gravity. It can reach a point where its velocity is high enough to keep falling but also keep missing the object it is falling towards. What keeps it from accelerating (because of gravity) and eventually reaching escape velocity? I feel like I'm either looking at things the wrong way or I have the entire thing wrong.
111205
When I was in school, I learned (from Democritus) that an atom was  similar to a solar system, with the nucleus being the sun, and the  electrons being the planets. Of course, there are some differences:    The "sun" isn't a single entity, but a collection of protons and nuetrons.  Two planets can share an orbit (which might be possible in a solar  system too, but it doesn't happen in our solar system).    Is this model still valid? Here are my problems with it:    In "Surely You're Joking, Mr Feynman", Richard Feynman implies  that electrons are more a theoretical concept than real objects.  I have trouble understanding atomic bonds (ionic and covalent) in  this model.  I also have trouble understanding electron "orbit jumping" in this  model, as well as several other things.    Is there a better model for someone learning this for the first time?
88982
You have likely read in books that tides are mainly caused by the Moon. When the Moon is high in the sky, it pulls the water on the Earth upward and a high-tide happens. There is some  similar effect causing low-tides. They also say that the Sun does the same as well, but has smaller effect compared to the Moon.  Here's my question: Why is the Moon the major cause of tides? Why not the Sun? The Sun is extremely massive compared to the Moon. One might say, well, the Sun is much farther than the Moon. But I've got a simple answer: Just substitute those numbers in $a=\frac{GM}{d^2}$ and find gravitational acceleration for the Moon and then for the Sun (on Earth, by the way). You'll find something around $3.38$ $10^{-6}$ $g$ for the Moon and $6.05$ $10^{-4}$ $g$ for the Sun - I double checked it to make sure. As you can see, the sun pulls about $180$ times stronger on the Earth. Can anyone explain this? Thanks is advance.
31536
Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck.  As I understand it, the solar system evolved from a massive molecular cloud. To me, this seems to break the second law of thermodynamics, as I think it suggests order from disorder.  I know there must be something wrong with my logic, but am really stuck.  Can anyone explain this one in layman's terms?  (Posting to both "Astronomy" and "Physics", as it seems to overlap these subjects)
44383
As shown in the Manga and the Anime, Enel survived along with the Ark.  He then Embarks to Fairy Verth      The Moon.   In the Manga it shows his adventures on the Moon.  But what happened?  I didn't understand the situation that happened.  What exactly happened on the Moon?
15190
In an older question from June 2011, , apparently revived by the system, a user is asking about the origin of the rotation of celestial bodies.  The  (with 17 votes) states the following:     When things collapse under their own gravity in space (i.e. clouds of gas and dust), any small amount of asymmetry in the collapse will be enough start it spinning.   And then it goes on saying:     Even if it spins by a tiny amount, as it collapses, angular momentum     conservation will mean it spins more and more quickly.   Is all this really correct?  I could try to ask in a comment to the answer. I actually did. But the author is no longer registered.  Hence I am asking it as a question.  But that is not the end of the story. As I was about to ask my question, I looked for other relevant questions, and there are some. I did not make an exaustive survey, but I did not find one that had satisfactory answers:    (december 2011) has just one accepted answer (0 votes) stating essentially that the solar system has angular momentum because it started from a cloud that had angular momentum. No comment.  (july 2011) is questionning about everything from galaxies to electrons. The answers are of a much higher quality, but while they seem to justify the possiblility of spin and angular momentum (and its conservation), there are not clear on how it appears, at least for celestial bodies.  (june 2013): That was my own very naive first question on this site. It is related but does not directly address spin.   One answer I found is that momentum appear from bodies in relative motion past each other. Nice, but not really an answer: where did they get their relative speed to begin with. Unfortunately the answer is: from the angular momentum of larger structures they belong to (well, it can be more comples). So this is just chicken and egg explanation. But how did it get started?  Note that my question is not a duplicate, since it is primarily whether the above statements are correct, which is not considered in these other questions.  Furthermore, these questions are fairly old, and given that none had received answers that seem to answer the question of the origine of existence of celestial angular momentum (not in a way I can understand anyway), it may be appropriate to attempt restarting the process, with the above discussion to motivate that an answer should explain the physical mechanism that started the existence of spin of celestial bodies.
62225
On , it is written that      So, we see things falling with an acceleration which we call the acceleration of gravity,and thinking that we live in a straight line , uniformly moving or stationary inertial frame, we attribute that acceleration to a force, the force of gravity. Whereas in reality,objects falling towards the Earth are moving along geodesic paths with no acceleration and according to modified version of law of inertia, have no force acting on them. They fall simply because the curved space-time near the Earth ...   Now, why do the objects falling towards the Earth move along the geodesic paths with no acceleration? That means the objects don't have any force acting on them, but why? A body in a free-fall moves with acceleration $g$, so, why is it written like that? Why does the author use Law of inertia on freely falling body?? Law of Inertia can only be applied when no external force acts on the body. So, is the freely-falling body accelerates under force of gravity or moves uniformly while moving through geodesic paths as quoted by the author?
86339
As we all know the Death Star is spherical. I don't know if it generates gravity on its own or has a gravity generator, but that's not important. I think we have basically two scenarios:    Gravity works the same way as Earth. If you are in the lower hemisphere, you are upside down, but that's normal for you.  If that's the case, when would the gravity shift? What if you're taking an elevator, would it be same as in the Total Recall remake? Everyone has the same gravity. Same as if you were in one big house.  Now what if the trench ran in the lower hemisphere. Would the stormtroopers in the turrets be upside down?   I accept any sort of canon.
1300
According to , there are 5 equilibrium, or  of the Earth-Moon system and only 2 of them are said to represent stable equilibrium points.     This made me think if there is an equation that describes this system, and from which Physics Laws was it derived?
71284
Possible Duplicate:          Today we were in our Literature class talking about the Renaissance and the Enlightement and our teacher also said that scientific experiments were being conducted, and she gave as an example the experiment in which they dropped objects with different mass from a tower to see which object would land first. She then said that she herself didn't know the outcome and since I'm known in my class as the #1, they asked me and I said that they landed at the same time (to my shock many classmates even disagreed with me about this fact). The teacher asked me to explain why and we haven't had anything about inertia in our physics class, so I was forced to use my own self-thought knowledge of physics: I said gravity does pull harder on heavier objects, but heavier objects have more resistance to move, in other words, they have more inertia. The entire class except for the teacher disagreed with me even though they usually don't. One fairly annoying kid asked me to explain why a feather falls way slower than a bowling ball, and I explained why and I also made the claim that in a vacuum they would fall at the same rate. Was I right or my class? Of course I know my explanation is lacking, but it has truth to it, right?
2678
Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum.   From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational field is physically indistinguishable from floating in interstellar space. This would make sense to me if gravity simply caused an object to move at a constant velocity. Moving at a constant speed, or floating in space, are just two different ways of describing an inertial frame, and are fundamentally no different. But free falling in a gravitational field means accelerating continuously, and doesn't an accelerating body experience a force? Then isn't free falling fundamentally different from floating in space?
23451
If a planet was suddenly stopped in its orbit supposed to be circular, show that it would fall onto the sun in a time $\left( \frac { 1 }{ 4\sqrt { 2 }  }  \right) $ times its time period.   I am getting stuck with this problem. I have applied conservation of energy and I think it may solve it. Please help. Here's my research on the problem:   Firstly, ${ T }^{ 2 }=\frac { 4{ \pi  }^{ 2 }{ r }^{ 3 } }{ GM } $. Assuming $v$ to be the velocity of the planet at a distance $s$ from the sun, we get: $\frac { m{ v }^{ 2 } }{ 2 } +\left( \frac { -GMm }{ s }  \right) =-\frac { GMm }{ r } $, where $r$ is the radius of the planet's orbit.
39442
If two bodies are close, both will get attracted to each other and collide. Under what conditions will the two bodies start revolving around their common center of mass? I understand that such bodies represent the gravitional two-body problem, but I want to know what are the initial conditions that allow it so settle into such a configuration (without going into the maths)
90102
Related:   I was learning about GPS satellite orbits and came across that Low Earth Orbits () have a period of about 88 minutes at an altitude of 160 km.  When I took a mechanics course a couple of years ago, we were assigned a problem that assumed that if one could drill a hole through the middle of the Earth and then drop an object into it, what would your period of oscillation be? It just happens to be a number that I remembered and it was 84.5 minutes (see ). So if I fine-tuned the LEO orbit to a vanishing altitude, in theory, I could get its period to be 84.5 minutes as well. Of course, I am ignoring air drag.  My question is: why are these two periods (oscillating through the earth and a zero altitude LEO) the same? I am sure that there is some fundamental physical reason that I am missing here. Help.
100405
It's a classic question with many answers all over the Internet, but none here so I figured I'd ask it:  How fast would the Earth need to spin for a person (or anything for that matter) to feel weightless while on the surface at the equator?    In this situation everything on the Earth's surface would essentially be in orbit around the Earth at the radius of the Earth's surface (let us assume the atmosphere was also spun up to this angular velocity so there would be no air drag slowing things down).  Let us also say by "surface of the Earth" we mean mean sea level.  You can decide for yourself if/how to factor in the bulge of the Earth.  You can assume that the Earth somehow is able to maintain its present shape while spinning up.  Any comments on whether an Earth spinning slightly faster than this speed will cause it to break apart or not will also be appreciated.
117345
I recenty got my essay back from my teacher and she said that it was wrong to use upper case "Earth". When I'm writing Earth, I'm referencing to the planet Earth, not soil. This is the sentence which included "errors". She gave me an error in every word that I marked with strong first letter.     This is why the Moon orbits the Earth, and the Earth orbits the Sun, and the Sun orbits the black hole in the middle of the Milky Way.   Who is right, me or her?