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First post. Hello, my name is Davin. Questions.

  1. Oct 24, 2003 #1
    I am not a rocket scientist, I have never taken calculus, I do not have a degree of any sort, I have dropped out of high school, I can bearly spell words correctly, and I'm just a young punk kid. But I do have many questions that have been bothering me incessantly since I was 15 and took physics 20. These questions have lead me nowhere because University professors won't return my calls, my highschool teachers never seemed to give me a satisfying answer (they just tried to confuse me to avoid saying they didn't know), and the internet hasn't been much help in terms of articles or actually answering my questions. And now I am finally (after a few years) attempting to get real answers. The questions are as follows:

    1. Is there a speed of gravity?
    This is one of the first questions I asked myself when thinking about gravity. My physics teachers all told me that it was, like everything else, limited to the speed of light. But that just does not sit right with me. Does that mean to say that if the sun just dissapeared the planets would continue their orbits for 8 seconds or whatever the time it is for the light to reach the earth? Would this not make space travel increadibly complicated in terms of mathmatics? Wouldn't the sun's gravity be affecting earth 8 minutes (I'm just assumeing the time) behind it's actual position?

    2. If there is a speed of gravity (and possibly if there isn't one) could gravity be blocked/diverted/deflected?
    The only thing I could think of, with my non-existant education, to modify gravity would be magnetisim. With just fridge magnets to use I could see that gravity and magnetisim behaved in very similar if not identical ways. If magnets only acted on certain elements, then could gravity not just be a magnet for matter (assuming things exist that are not matter)? And would that mean that there is a measureable speed of magnetisim?

    3. Does gravity need a medium to travel?
    Does gravity travel in waves like light? Or through the vibration of something like sound? And if gravity is instentanious and needs a medium, then couldn't we find and tap into that same medium for faster than light communication?

    4.Could gravity be a push?
    This was just an idea I had, it pretty much came out of nowhere and I was just wondering if gravity was like water or air pressure, and was an unseen force pressing down on us.

    5. Why does gravity weaken?
    Does that inherently mean that it has a speed and needs a medium to travel? Why would gravity wear off after a distance?

    6. What is the nature of centrifugal/centripital force?
    I'm pretty sure centrifugal force is just there because spinning could be seen as moving in a direction for a fraction of time, then being diverted in another direction causeing you to be pushed against your car door or what have you. But would forces such as that be able to extend beyond the borders of whatever is making them move?

    7. Would a perpetual-motion-gravity-electric-generator be possible?
    This is what I had envisioned but it's only in my head and ive never tried it: You have a large tank of water suspended in the air. Then you open one of two holes in the tank and it pours water into one of two buckets suspended by chain, connected to a pulley, so that it becomes heavier and sinks, spinning the pulley and raising the other bucket, the bucket then hits a bar off-center to drop the water into another basin connected to the top basin via pipes. The bottom basin would already be full of water and hold more volume than the top so that the bucket-water weight forces the water back up to the top (I hope). The pulley's spin will do all sorts of jobs (via gears); firstly it would generate electricity (I never learned how, spinning + something else, maybe magnets? makes electricity is all I know) as well as run a pump to push the bottom basin's water back to the top basin, and open the other hole to fill the other bucket. Repeat process. Or could you even "tap" into gravity?

    I have more questions and ideas but I can’t think of them just now, It’s very late and I haven’t slept for a while. I’m sorry if these questions are stupid and pointless, it’s only stuff I’ve thought of while trying to fall asleep. Like I said, I couldn’t stand highschool so I dropped out (2 years ago, I’m 19). Maybe I’ll get my G.E.D....

    P.S. Even if my ideas are stupid, please tell me why they are.
  2. jcsd
  3. Oct 24, 2003 #2


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    1. The current state of Physics holds that the speed of gravity is c. Gravity is a very weak force so there is, currently, no known way of measuring it.

    2. An even better question is "How do you make the sun vanish?" attempt to stick to moderatly realist questions. If you wish to write sci fi then you can feel free to answer that question. But yes if the sun were by some form of magic vanish it would be 8sec befor the earth knew it.

    3. The medium of gravity is space-time. Gravity is distortions in space time caused by the presence of massive bodies.

    4. All data indicates that gravity is a pull. Seems to make more sense to me, at least when it is seen as a pull between 2 bodies we only need to consider those 2 bodies, what is pushing?

    5. The force of gravity drops off as 1/r2. Basicly this is because it has a spherical symetry so the force changes like the surface area of a sphere.

    6. Circular motion is the result of a force towards the center of the circle. This is the centripetal force, observe how you pull on a string when swinging something in a circle. That is the centripedal force. The object at the end of the string feels the centripetal force, your hand which is exerting the centripetal force feels the centrifugal force, this last is not a real force it is mearly the result of a centripetal force.

    7. No. All systems have some sort of loss this means that it will always take more energy to drive them then you can get out. Remember that you first have to fill the big suspended tank with water. If you say, let it fill with rain water, then it is mother nature doing the work for you. We call it hydroelectric.
  4. Oct 24, 2003 #3
    I think it's good idea to propose hypotheses.
    Lots of good theories are answers to hypotheticals.
    In this case, asking ourselves the question of a spontaneously disappearing sun might lead to unexpected and groundbreaking answers.
    Don't forget, we frequently imagine spaceships at velocity 0.999 C to discuss special relativity and so on and so on...
    Didn't someone say, finding answers is relatively easy. It's asking the right questions which is the hard part.
  5. Oct 24, 2003 #4
    Don't put yourself down.
    School was the worst part of my life too, even though some of my teachers were great people.
    I'm 34 and started higher education part-time distance-learning two years ago.
    I have low paid job and things are not always easy but I'm thinking ahead to another 4 years and I'll have my education and be able to get a job which I really want ( mathematics ).
    It's never too late.
    Forget your bad experiences and go to school as an adult student, or, take a distance-learning course if you don't want to see other people ( I'm doing distance-learning and am really enjoying it ).
    You obviously are interested in physics and stuff, so learn what you're interested in.
  6. Oct 24, 2003 #5
    The speed at which changes in the gravitational field propagate is the same speed at which changes in the electromagnetic field, or any other field, propagate: the speed of light.

    The laws of physics cannot predict what would happen if the Sun disappeared, because that would violate the laws of physics (conservation of mass-energy): the laws will give meaningless, inconsistent answers. But you can ask what would happen if, say, you shook the Sun back and forth (very hard, but not theoretically impossible): then yes, the Earth would continue in its orbit for another 8 minutes or so before it "noticed".

    Well, the math isn't as simple as it is in Newtonian gravity (in which gravity propagates instantaneously), but the mathematics can be done. You have to work with retarded potentials and such. This is no different than electromagnetism, by the way.

    Not really. The reason why you can block/divert/deflect electromagnetic waves is because charge has two signs, so you can get into situations in which there are cancellations. But mass only has one sign.

    By the way, the "speed of magnetism" is the speed of light, because light is just an electromagnetic wave.

    No and yes, respectively.

    This is a very old idea that is frequently re-invented by laymen, but all "push" theories of gravity have failed.

    Well, there are various ways of approaching this question. There's no intrinsic reason why all interactions have to drop off with distance; the strong force increases with distance (which explains the phenomenon of quark confinement). So in principle such forces can exist, it's just that gravity doesn't happen to be one of them. I'm not sure how else to answer your question: we don't know why any force exists as opposed to any other force, we just know that they do exist.

    Centripetal force is a real force, an inward force that makes an object move in a circle. (Like the tension in a string, a gravitational force, the electrical attraction of an atomic nucleus, etc.) Centrifugal force isn't a real force: if you get spun around, there isn't a force forcing you to the outside. It's just that your natural inertial motion in the absence of force is to move in a straight line, but you're also being accelerated inward, so the force-free linear motion is actually "outward" relative to the centripetal force.

    Not according to the known laws of physics. Your proposal won't work, for instance, because the system is not perfect: some energy will always be lost due to friction, heat, evaporation of water, etc., and the machine will eventually run down.
  7. Oct 24, 2003 #6
    I want to go into more detail with you about your second question because I did alot of thinking about the very same things when I was first starting to find out about physics.
    Alot of people trying to come to grips with gravity are compelled to examine magnetism. As a force capable of attracting things, it is "the usual suspect". The better you get to know both gravity and magnetism, though, the clearer it becomes that they are two quite different things.
    Now this bothers me, because it means you must have been ignoring something very important about fridge magnets: If you have two stuck together and turn one over the attraction turns to repulsion. There is no analog for this in gravity. We cannot flip anything over and get repulsion from the earth. So, I don't know why you see the behaviour of fridge magnets as "similar, if not identical" to gravity.
    The way gravity works is that all matter attracts all other matter, no matter what position anything is in relation to anything else.
    Magnetisim is quite different. Magnets are "dipoles". There is always a "north" pole and a "south" pole (these names are arbitrary convention just to keep track of the fact that one is different than the other) Every "north" pole repells all other "north" poles. Every "south" pole repells all other "south" poles.
    Every "north" pole attracts every "south" pole. Like poles repell, unlike poles attract. Gravity has no qualities similar to this.
    Someone has already answered this but I'll include an example: If you wrap insulated wire around a piece of steel many times, then hook the two ends of the wire up to battery, as soon as you complete the electrical circuit a magnetic field will ballon up fron the wire and steel traveling out in all directions at the speed of light. This means that in less than two seconds the magnetic field you have created will have hit the moon.

  8. Oct 24, 2003 #7


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    Davin, Hello! I'll attempt #1 first. Speed being a rate of motion and the earth rotating on its axis with a speed coinciding with the gravitational pull of its mass, then, yes, I would have to say that gravity has speed.
  9. Oct 24, 2003 #8
    .This post is not based on current physical theory. Please disregard its contents.
    Scott, Please restrict your opinions to the theroy development fourm. If you continue posting responses such as this I will simply delete it.


    Hi Davin,

    For a minute there i thouht i was writing your post. You have clearly stated what intuitively we know to be false yet everyone is telling you it's true. They say gravity has speed "c" but they don't even know what light is. They say that gravity is different to magnetism but can't tell you what magnetism is. They will even tell you what electricity is but they don't even know what magnetism/gravity /light/ etc is. They will defend other peoples theories that are flawed in their premise and when put on the spot declare that you are stupid for doubting such erudite (learned)scientists.

    But Davin, this is the nature of it all. YOU intuitively feel there is error and at the moment you are prepared to ask questions that can not be answered properly and in full. Simply because we don't know the answers.

    They say that perpetual motion or energy is impossible because of what they call Conservative nature of energy etc. Yet you look around and you see perpetuality every where and of course you are going to argue against this presumption that it doesn't exist.
    They will tell you that everything ends at some point as a fact when they really don't know whether it had a begining in the first place.

    They will quote other peoples theories as fact because it makes them feel more secure in their knowledge.

    Davin, You are really up against it. And if I were you I would recognise it as a fools paradise and get on with some other endeavour. But I also know you, like me, wont because you see something that doesn't make sense and like all the other scientists you want to make sense of it.

    Being a "punk" kid is no weakness in fact I would call it a strength.

    Trust your intuition, modify it with a little knowledge and go for it.

    Because it is only the doubting of existing beliefs that allows one to move forward. If you accept that others have the answer when they don't, you are sharing in their delusions
    Last edited by a moderator: Oct 25, 2003
  10. Oct 25, 2003 #9
    scott_sieger ,

    There's a place for people like you, it's called sciforums.com
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