# Gravity???

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#### jschaef5

##### Guest
I am still wondering how much of an impact the gravity created from protons and neutrons effect the electrons. Is gravity the same at a small scale like this, just as the planets circle the sun, the electrons orbit the nucleus in the same manner? <div class="Discussion_UserSignature"> </div>

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#### dan9678

##### Guest
Re: “My point is, there is a discernible difference.”<br /><br />Actually, most of what I said is not exactly my crazy idea. I’m simply sewing together bits and pieces that I’ve read. The idea that there is no discernible difference between acceleration from gravity and accelerated motion is Einstein’s equivalence principal. <br /><br />I think Einstein’s observation offers some insight into the nature of gravity. Another insight comes from a special case of accelerated motion: A spinning bucket of water. When you spin a bucket of water, the water inside the bucket will start to take on the motion of the bucket. As the water starts to spin faster, the water is accelerated toward the walls of the bucket causing the surface of the water to take on a concave shape. Now here is the weird part: how does the bucket and water know that it is spinning and with respect to what point of reference? If it were just you and this bucket alone in the universe and no other point of reference (like stars planets…) from your perspective it would be impossible to say whether you were orbiting the bucket very quickly or the bucket itself was spinning. Oddly, you can test what is actually happening by simply looking at the surface of the water. If it is concave, the bucket is spinning. If not, you’re orbiting a bucket of water. I think spacetime is that hidden and normally static point of reference that lets you determine the difference between a spinning bucket and you orbiting the bucket. I say normally because in the presence of a large mass, it ceases to be static. I think <br /><br /> -Dan-<br />

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##### Guest
It seems that spinning bucket only works in a gravity or artificial gravity field but how does it know that. The suns gravity is pulling me with immense force but I can't feel it so is it even a force. Some-days I think it is 'cos I can see where it's <i>equal & opposite reaction</i> is & other days I'm not sure.

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#### nacnud

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The gravitational attraction between a proton and an electron is negligible compared to the other forces involved.<br /> <br />No electrons don't orbit the nucleus in the same way a planet orbits a sun. The best model we have of subatomic particles is quantum mechanics which is very different to the models we have for planets, namely general relativity.<br /><br />In quantum mechanics particles have quantised energy states, can be represented by particles or waves or both, and generally don't behave as you would expect.<br /><br />General relativity uses continuous distributions and although there are some interesting effects at high energies the low energy approximations are the same as Newton’s laws of motion and gravity.<br /><br />The two theories are very different beasts and although both electrons and planets can both be said to be in orbits the descriptions of these orbits are not compatible.

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#### jschaef5

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So why does gravity not effect a particle. Isn't gravity based soley on the distance and ratio of masses? Shouldn't an electron orbit the nucleus in the same manner as planets do around a star? <div class="Discussion_UserSignature"> </div>

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#### nacnud

##### Guest
<font color="yellow">So why does gravity not effect a particle.</font><br /><br />Gravity does effect a particle <img src="/images/icons/smile.gif" />, it is just that compared to the other forces involved, namely electromagnetic, is many orders of magnitude smaller.<br /><br />For example consider two protons separated by the distance of a protons diameter (2*10^-15m)<br /><br />Gravitational force is around 10exp-34 Newtons<br />Electromagnetic force is around 10exp2 Newtons<br /><br />That’s a difference of 36 orders of magnitude! So for subatomic particle gravity is all but negligible.<br /><br />Have a look around wikipedia.org for much more detailed info. As a starting point the Bohr model of the atom shows how electron levels are discrete energy levels where the governing force is electromagnetic rather than gravity as in planetary orbits.<br />

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#### jitte

##### Guest
Here is a isting of links to 37 different theories on the nature of gravity. It makes for some interesting reading.<br /><br />37 theories<br />

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#### nikshliker

##### Guest
dan9678: <br /> The bucket idea you explaned is an unanswered question i have read a lot about. The just of the nswer is....there is no answer. some people "think" that the bucket will hold the same prperty, meaning the mass inside will still be pushed up againsted the side and due to friction start to rotate creating a whirlpool looking thing. (this is ignoring the fact that if you were in space that the water would NOT stay in the bucket.) This theory would require an absolute frame of freference. a made up entity that you cant observer but can use as a tool. Newton called this absolute space. He said that if the bucket begins to spin the water wont begin to spread outwards because it is stil not accelerating in repsect to absolute space. Once the friction makes the water spin it will begin to spray outwards and make a concave appearance. This is only what newton thought. The strange thing about what newton said was that he knew he was only paving the foundations for physics and that his ideas would be changed drasticly. Newton loved space!!!

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##### Guest
Does that break reciprocity?

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##### Guest
Yoics! lots of mention of aether, well I think so but it's spelt as the anaesthetic.

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#### nikshliker

##### Guest
with nothing else to put it in reference it seems the logical answer. in the descirbed expirement e have a bucket, water, and nothing. you cant set the frame of reference to the wternor the bucket......what is left? the nothing. <br /><br />would it be possible to average the velocities of every particle in the system and call that stationary? as a frame of reference. that way we dont need to call it aether <img src="/images/icons/smile.gif" />

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##### Guest
Gravity can't possibly be internally generated as it's speed has recently been proved to be the speed of light. It thus couldn't escape from a black hole, which would be invisible to other matter & not highly attractive. Talking of attraction, the recently measured speed of gravity is in the opposite direction from it's force. Please please how is this? is it clawing it's way through space thus pushing back against any object? like a car's wheel does against the road. If so, of what are it's claws made?

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#### jitte

##### Guest
"Gravity can't possibly be internally generated as it's speed has recently been proved to be the speed of light."<br /><br />One of the theories on the nature of gravity in the link to a list of 37 is the Gravity is the 4th Dimension theory. It looks at it from the standpoint of geometery, with each dimension moving at right angles out of the preceding dimension.<br /><br />A one dimensional line moves at a right angle out of a non-dimensional point, a two-dimensional plane moves at a right angle out of the line, and a three-dimensional cube moves at a right angle out of a plane. Gravity, the 4th dimension, moves at a right angle out of the cube and can be envisioned as a smaller cube (the 3rd dimension) suspended within a larger cube (the 4th dimension).<br /><br />I haven't read all 37 different theories on the list, but think this one is interesting. <br /><br />_________________________

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##### Guest
I've not read them all which is why I joked about anaesthetic 'cos it was blanking my mind <img src="/images/icons/laugh.gif" /> I've copied it so's I can dip in & out.

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#### dan9678

##### Guest
It's true, I think the argument for absolute space is pretty much dead. However, that experiment does show a distinct connection between the inertial properties of matter and something. Somehow the bucket knows it is spinning. And I think that something is spacetime. <br /><br />Keep in mind, this is just my opinion. You are correct when you say 'there is no answer' (So far).<br /><br />

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#### eltorrente

##### Guest
So.. shouldn't a bowling ball actually fall faster than a feather in a vaccuum? Every object exerts gravitational influence, and a bowling ball has more mass than a feather.. so shouldn't it fall faster?<br /><br />How can 9.81xxxx be *THE* number in all circumstances on earth? What if I took a cup-full of nuetron star and dropped it- wouldn't the 9.81 number be much, much higher in that case? - and if it is indeed higher, than why not in all cases- including bowling balls and feathers?

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#### igorsboss

##### Guest
<font color="yellow">So.. shouldn't a bowling ball actually fall faster than a feather in a vaccuum? Every object exerts gravitational influence, and a bowling ball has more mass than a feather.. so shouldn't it fall faster? </font><br /><br />Yes, the force of gravity is greater on the bowling ball than it is on the feather, because the bowling ball has more "gravitational mass" (M) than the feather.<br /><br />However, the "inertial mass" (m) of the bowling ball is also greater than the mass of the feather. It takes more force to accelerate a bowling ball than it does to accelerate a feather, when accelerated in the same way.<br /><br />Now consider any object with gravitational mass M and inertial mass m, in a gravitational field where the force of gravity equals Mg. Let's find out how fast will this object accelerate?<br /><br />Newton's law says f=ma.<br />From Gravitation, since f=Mg in this case, Mg=ma.<br />Solving for acceleration, we find that (M/m)g=a.<br /><br />Now, it just so happens that every time anyone has ever measured them, the gravitational mass and the inertial mass have been found to be EXACTLY EQUAL IN ALL CASES. Why is this so? Nobody knows! Turns out this is a very deep mystery!<br /><br />Knowing this, we realize that M=m, so (M/m)g=g=a.<br /><br />The inertial and gravitational masses cancel out!! That's why the feather and the bowling ball fall at the same speed (on the moon).<br /><br /><font color="yellow">How can 9.81xxxx be *THE* number in all circumstances on earth?</font><br /><br />It isn't! This is just an approximation that works pretty well for most stuff. Variations come from changes in the local geology.<br /><br /><font color="yellow">What if I took a cup-full of nuetron star and dropped it- wouldn't the 9.81 number be much, much higher in that case? - and if it is indeed higher, than why not in all cases- including bowling balls and feathers?</font><br /><br />Again, the variations come from the local geolo

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#### igorsboss

##### Guest
<font color="yellow">So.. shouldn't a bowling ball actually fall faster than a feather in a vaccuum? </font><br /><br />As above, the bowling ball and the feather would accelerate at the same speed.<br /><br />However, Earth would accelerate towards the bowling ball faster than it would accelerate towards the feather!!<br /><br />So YES, the bowling ball will hit the ground sooner than the feather, but the difference in timing is so slight that it is beyond our ability to measure.

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#### killium

##### Guest
That's my way of seeing it:<br />The bowling ball is more massive (than the feather) so it has more gravity force acting on it. But, the bowling ball is more massive so it needs more force to be moved,... by exactly the same amount so, this cancels out and "everything" moves at the same acceleration.<br /><br /><br /><br />For the bucket with water, I think the problem with this is that we consider that the water "has to know" if its moving or not to be influenced by the centripete force. In fact, the water doesn't know and doesn't have to. What makes the water going into a concave shape is because the wall of the bucket is pushing it. The water, having received momentum from friction with the wall of the bucket, "wants" to continue to move in straight line and cannot. It is only a question of inertia.....again!<br /><br /> <div class="Discussion_UserSignature"> </div>

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#### eltorrente

##### Guest
"However, this would not be an inertial frame of reference! An observer in an inertial frame would see the Neutron star accelerate towards Earth due to Earth's gravity, and the Earth accelerate towards the Neutron star due to the Neutron star's gravity. "<br /><br />Thanks for the reply! I sorta understand <img src="/images/icons/laugh.gif" />. Can you explain what an "inertial frame of reference" is?

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##### Guest
jschaef5<br />"<font color="yellow">I just don't get gravity. How does it work.</font><br />Gravity is a bending of space and time that is more pronounced near a massive object than further away. An object moves closer to a massive object because each second there is less space between them. Since the space removed for a feather and a bowling ball are the same, they respond to gravity at the same rate.<br /><br />bbk1<br />"<font color="yellow">Does the speed of planet rotation have any effect on gravity?</font><br />If the rotational speed of the Earth were 17 times faster than it is now, then centripetal force would exactly cancel gravity, so you would appear to weigh nothing.<br /><br />If the Earth did not rotate, then at the equator 1/17th of your weight would no longer be canceled by centripetal force, so you would weigh 1/17th more than you do now. If you mass 90 kg, what I do, then if the Earth did not rotate you would feel like you massed 95 kilos. It's not much, but it's measurable.<br /><br />"<font color="yellow">So does gravity originate from within objects or is it some external force?</font><br />Gravity is a property of mass, meaning that if you have mass then you have gravity. The better question therefore is why does mass have gravity? I have an opinion, but it is not mainstream science, so I will caution you to avoid accepting the opinion. I believe that space-time is another side to matter-energy. If you create matter-energy, then you also create space-time. The approximate equivalent would be about a hundred liters of space for a one proton mass. You can create or destroy matter-energy without violating the conservation of matter and energy provided that you re-word the law to be the conservation of matter, energy, and space-time.<br /><br />Note that if you create matter-energy, then the accompanying additional space-time would put extra distance between objects. By postulating a universe that is creating more

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#### kmarinas86

##### Guest
<font color="yellow">If the Earth did not rotate, then at the equator 1/17th of your weight would no longer be canceled by centripetal force, so you would weigh 1/17th more than you do now.</font><br /><br />well say your equator weight is 16virtual/17actual of your north pole weight (huh?) then 17virtual/17actual would be your north pole weight, from 16virtual/16initial to 17new/16intitial, or 1/16th more.

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#### newtonian

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igorsboss - OK-why don't we know why gravitational mass and inertial mass are equal, exactly?<br /><br />Or are they?<br /><br />Have we actually determined why those space probes are slowing down?<br /><br />Or why universal expansion is accelerating?

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#### igorsboss

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<font color="yellow">Can you explain what an "inertial frame of reference" is?</font><br /><br />An inertial frame of reference is a frame of reference which is neither accelerating nor rotating. The equation f=ma is true in an inertial frame of reference.<br /><br />In an accelerated (non-inertial) frame of reference, an unrestricted object will demonstrate acceleration without an applied force.<br /><br />An example of an inertial frame of reference is an observer in a non-rotating box in freefall.<br /><br />As an example of a non-inertial frame, consider the bridge of your own nose as the origin. Since you are on Earth, and Earth spins, and Earth has gravity, and you are not in freefall, the physical law f=ma isn't sufficient in this frame of reference. The equation must be corrected for Earth's gravitational field. There is also a correction called the coriolis force, for motion constrained to the Earth's surface.

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#### igorsboss

##### Guest
<font color="yellow">why don't we know why gravitational mass and inertial mass are equal, exactly?</font><br /><br />Gravitational mass is that property of matter which gives rise to the warpage of space-time which we call gravity.<br /><br />Inertial mass is that property of matter which gives rise to the property of matter called inertia. Inertia is the ability of matter to resist being accelerated by whatever force is applied, whether that force is gravitational or not.<br /><br />Gravity and inertia seem to be very different properties of matter. How are these two properties of matter connected?<br /><br />There does not seem to be any fundamental reason why these must be identical. However, they are found to be precicely identical in every experiment we've ever tried.<br /><br />Why is that? I don't know! It just is!

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