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Meaning of gravity in an intuitive sense?

  1. Jan 7, 2006 #1
    meaning of "gravity" in an intuitive sense?

    A very very general question:
    Can anyone explain the meaning of "gravity" in an intuitive sense?
  2. jcsd
  3. Jan 7, 2006 #2


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    Hi jrm. Could you elaborate upon your question, please? Essentially, gravity is the attractive force between any two bodies with mass. It is proportional to the amount of mass, and inversely proportional to the square of the distance between the centres of the objects.
  4. Jan 8, 2006 #3
    Thanks Danger:
    You said " gravity is the attractive force between any two bodies with mass."
    Let us say the bodies are say a pen and a pencil lying on the table.How will there be a force of attraction between them?
    Plz help!!
  5. Jan 8, 2006 #4


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    I don't believe that there are any devices on the planet sensitive enough to detect the gravitational attraction between a pen and a pencil, but it's there.
    Only one body is required to produce a gravity field, but examples are always given with at least 2 because the interaction between them is the only way to directly measure it. Also, the bodies are usually assumed to be spherical for simplicity. A lot of math would be involved in trying to figure out the shape of a field around something pen-shaped.
    The simplest way to think of it, although it's not quite accurate, is that the object causes a 'dent' in spacetime. Something that comes along, including a light beam, alters it's motion to continue in what it thinks is a straight line. Think of placing a ball bearing on a rubber sheet, then rolling a marble toward it. The marble has its own little 'dent' that travels along with it, but it's insignificant compared to the one made by the bearing. If both masses are the same, the two dents interact in a different manner than just one falling into the other.
    I'm afraid that I'm pretty much at the limit of how much I can explain it. Feel free to ask if you have more specific questions. I might not be able to answer them, but others on site can.
  6. Jan 8, 2006 #5


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    Using a torsion balance, we can directly measure the attractive force (tiny as it is) between lead balls.

    Google for "The Cavendish Experiment", one good link is at

    http://physics.usask.ca/~kolb/p404/cavendish/ [Broken]

    As to the mechanism of "how", one can take several views of various degrees of sophistication, but I don't want to get into a long explanation of GR if you are (for example) looking for a classical Newtonian explanation of gravity.

    I will say that experiments such as the Cavendish experiment confirm that gravity exists in the laboratory even between small objects. The measured values of gravity from such terrestrial experiments are also a good fit with astronomical observations.
    Last edited by a moderator: May 2, 2017
  7. Jan 8, 2006 #6


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    I remember seeing an utterly absurdly simple display of two objects gravitational effects. It was two balls maybe a foot apart on what i assume is a very very low friction rotating pipe system. The problem was that it had just rained so the electrostatic effects were far too great and overshadowed the gravitational effects. Does anyone know what I'm talking about? It looked like someone had just made it with some pvc piping.
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