What is Gravitational field: Definition and 369 Discussions

In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenomena, and is measured in newtons per kilogram (N/kg). In its original concept, gravity was a force between point masses. Following Isaac Newton, Pierre-Simon Laplace attempted to model gravity as some kind of radiation field or fluid, and since the 19th century, explanations for gravity have usually been taught in terms of a field model, rather than a point attraction.
In a field model, rather than two particles attracting each other, the particles distort spacetime via their mass, and this distortion is what is perceived and measured as a "force". In such a model one states that matter moves in certain ways in response to the curvature of spacetime, and that there is either no gravitational force, or that gravity is a fictitious force.Gravity is distinguished from other forces by its obedience to the equivalence principle.

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  1. S

    Gravitational field strength problem- help needed

    gravitational field strength problem-urgent help needed Homework Statement Moon has a radius of 1740km, Mass of 7.35 x10^ 22kg, grav field strength of moon= 1.62Nkg^-1, distance from Earth to Moon is 380000km G=6.67x10^-11Nm^2kg^-2 The Moon's gravitational pull on the Earth causes the...
  2. T

    Earth's gravitational field size.

    Is the size of Earth's gravitational field the same size as it's electric/magnetic field? Also, what is the standard theory as to why the Earth has a magnetic field? What I mean is, how is it generated? Is it the result of the Earth traveling through space and interacting with the rays etc...
  3. A

    How Do You Calculate the Magnitude of a Vector in the Form Constant * (i + j)?

    Homework Statement Homework Equations The Attempt at a Solution But as you can see, when I typed the answer on the answer column, the computer marked it as wrong. Please point out my mistake in 24 hours. Thank you.
  4. R

    Would Greater Electricity Affect a Gravitational Field?

    So I'm sitting here, reading about different ways to create gravitational fields as well as messing around with random thoughts and ideas, and this question comes to mind: Would greater electricity affect a gravitational field created by an electromagnet? Anyone who knows? I'd really like to...
  5. Truecrimson

    Gas pressure in gravitational field from the partition function

    Homework Statement Please see P2 in http://panda.unm.edu/pandaweb/graduate/prelims/SM_S09.pdf "Starting with \mathbb{Z} (z_1,z_2) above, derive expressions for the gas pressure..." Homework Equations The Attempt at a Solution To find the pressure at the top and the bottom of...
  6. N

    Gravitational Field: Particle Generated Force

    is gravitational field made with any particles
  7. G

    Hydrogen atom in a gravitational field

    hi does anybody of you know if there is an equation that describes an atom in a gravitational field of a star or something like that (general relativity or Newton)or do you know some results that could tell me something about the magnitude of this energy corrections? do you know a method...
  8. T

    Light bent in gravitational field

    i am new to GTR. Mytext book use an example to show ligt bendinf. when a light release from the back of the rocket which goes around the earth, since the rocket is in free fall, light would not bent relative to the rocket, but bent relative to earth. my problem is, is that means the amount...
  9. L

    Exploring Possible Speeds of Photons in a Gravitational Field

    Consider a photon moving in same direction with a gravitational field . So the speed of photon must become greater than speed of light. how its possible ? please answer this then I'll ask my next questions. :smile:
  10. I

    What is Gravitational field strength exactly

    Hello, I just read a book reagarding Newton and his laws and had few questions about it. What is Gravitational field strength exactly and what is Newton's universal gravitational constant? Aren't they the same thing? please explain these two concepts simple enough for me to understand and to...
  11. M

    Does an object lose mass when raised against a gravitational field?

    When an object (say a ball) is pulled some distance away from another object (say the Earth) against the objects' mutual gravitational attraction, does the mass of each object decrease? (Assume that the energy expended in moving the Earth and ball away from each other comes from within the...
  12. T

    'Mass' of an object at different positions in a weak gravitational field

    We had a physics lesson today on nuclear binding energy, where we looked at the mass of two protons and two neutrons independently and compared it with the mass of a helium nuclei, and were told how the discrepancy related to the release of energy during nuclear fusion. The first question in...
  13. R

    Why is the gravitational field considered a tensor field in GR?

    He who calls himself "Nabeshin" stated: "It seems to me the distinction can be best seen in the following: Differential geometry is mathematics, and this will tell us what the geodesics on a given manifold are. So if we're just finding geodesics on manifolds, maybe it's the manifold...
  14. C

    Difference between acceleration and gravitational field?

    This is something I've always wondered... Einstein's equivalence principle says that you can't tell the difference between being accelerated in an elevator, or being in a gravitational field. No matter what, there's no mechanical device you can build, etc. But, what about 'gravitons'...
  15. M

    Rocket in nonuniform gravitational field

    Hello, I'm trying to solve the rocket equation in a nonuniform gravitational field. The standard rocket equation at a distance x from the center of a planet of mass M gives: m*d^2x/dt^2 + v_e*dm/dt = -GmM/x^2 where v_e is the relative exhaust velocity. Multiplying by dx/dt and assuming...
  16. A

    Computing the action for a particle in a gravitational field

    A friend of mine told me he fielded this at an oral exam: "Compute the classical action S for a particle of mass m in a gravitational field U = -\alpha/r." I know the formula for the classical action is given by S = \int_{t_i}^{t_f} L(q,\dot q,t) dt, and that for a particle in a...
  17. I

    Gravitational field intensity at the center of the earth

    Homework Statement what is the gravitational field intensity at the center of the earth Homework Equations The Attempt at a Solution i was told that it was zero because you have the Earth's mass surrounding it, and graivty moves to the center of its mass (center of radius)...
  18. Q

    What Temperature Initiates Bose-Einstein Condensation in a Gravitational Field?

    Homework Statement For an ideal Bose gas in a uniform gravitational field, at what temperature does Bose-Einstein condensation set in. Gas is in a container of height L.Homework Equations Normal BEC temperature of an ideal Bose gas not under the influence of gravity is T = \frac{h^2}{2 \pi m...
  19. D

    Gravitational Field Strength and Acceleration on Mars

    How are the numerical values of gravitational field strength and acceleration due to gravity on Mars related?
  20. B

    Calculate Magnitude & Direction of Gravitational Field at 4th Corner

    1. Three objects of equal mass are located at three corners of a square of edge length d. Find the magnitude and direction of the gravitational field at the fourth corner due to these objects. (Use the following as necessary: G, d, and m.) 2. Homework Equations : g = Gm/r2 3. My attempt...
  21. Y

    Rotation of a vertical cylinder in a gravitational field

    Consider the above rotating vertically aligned cylinder in Schwarzschild geometry. Would anyone agree or disagree with the following analysis? If a local observer at the highest end of the cylinder measures that end of the cylinder to be (say) 2 rpm, then another local observer will measure...
  22. B

    Xxx Trajectory in a gravitational field

    **!xxx Trajectory in a gravitational field Assume an object comes from infinity and passes by the sun at 2 solar radiuses from its center. Can you derive an equation describing the objects path using only escape velocities and C??
  23. G

    Mass equivalence and instantaneous gravitational field

    Here is Max Born explaining the crash of a train, in which the train is regarded to be at rest: There are two peculiar features of this gravitational field: 1. Causation. The field appears coincidentally with the collision of the train with an obstacle. If a passenger had pulled the...
  24. W

    Gravitational Field: Proton & Electron Mass Ratio

    Homework Statement if a proton and a electron put in a gravitational field, what is their ratio compare to one another? Homework Equations fg= GMm/r^2 mass of a proton = 1.67 x 10^-27 kg mass of a electron= 9.11 x 10^-31 kg The Attempt at a Solution i tried to divided them out, i...
  25. H

    Optimal mass distribution for maximal gravitational field

    Homework Statement Suppose that one is given a lump of clay of total mass M and constant density. Let P denote a particular point in space. In what way should one shape and position the clay so that the gravitational field in point P is maximum possible? It is assumed that the clay stays in...
  26. e2m2a

    The speed of light in a gravitational field

    Does a photon gain speed if it travels in "free-fall" toward the earth? A particle of mass gains speed as it free-falls to the earth, and yet, mass is just another form of energy. Light is energy. So, does light gain speed?
  27. T

    Can gravitational field strength equal the centripetal acceleration?

    As a homework question, it asks, "...if the Earth were rotating so fast that the objects at the equator were apparently weightless?" Somewhere, someone said that, quote: In order for the rotation of the Earth to cancel weight, the gravitational field strength should equal the centripetal...
  28. Mmm_Pasta

    Gravitational Field Problem - Integrate?

    Homework Statement A nonuniform thin rod of length L lies on the x axis. One end of the rod is at the origin, and the other end is at x = L. The rod's mass per unit length λ varies as λ = Cx, where C is a constant. (Thus, an element of the rod has mass dm = λdx.) Determine the gravitational...
  29. K

    Lagrangian Equation of motion for rod on pivot in gravitational field

    Homework Statement I am trying to get an equation of motion for the following (seemingly simple) setup. You place on a rod on a pivot. The rod's centre of mass is precisely over the pivot. Think of balancing a ruler horizontally on your finger. Gravity, of course acts downward. The...
  30. S

    Calculating Angular Speed for a Gravitational Field of 1.95g

    Homework Statement A biologist studying plant growth and wants to stimulate a gravitational field stronger than the Earth's. She places the plants on a horizontal rotating table in her laboratory (on Earth) at a distance of 42.3 cm from the axis of rotation. What angular speed will give the...
  31. J

    How do you envision a gravitational field?

    For many years, i have struggled with the concept of a "field", and i basically simply have no idea what a field is or how it operates, whether it is a magnetic field, gravitational field or other. when you think of a gravitational field, as per GR, you think of "curved spacetime", but what...
  32. T

    How Do You Calculate Gravitational Field Strength Between Two Planets?

    Homework Statement Write an expression for the gravitational field strength E at a point distance r from a planet of mass M. (In my diagram, there are two planets with mass, m and distance 2a apart) Homework Equations The Attempt at a Solution The resultant gravitational field...
  33. G

    Question on gravitational field

    Homework Statement Considering only the gravitational fields of the Earth and the Moon, find the distance from the Earth at which a space capsule traveling between the Earth and the Moon is subject to zero gravitational force. Mass of the Earth = 5.98 x 1024kg Mass of the Moon = 7.35 x...
  34. J

    Position as a function of time throught a varying gravitational field

    I've been told this is a differential equation, but I have no knowledge of the subject, so I'm hoping it is and that an answer can be found in this forum. The two equations x=1/2at2 and a=gm/r2, when r is replaced with (r0-x), with r0 being the initial radius from the mass from which the...
  35. J

    Position as a function of time through a varying gravitational field

    I've been trying to figure this out for a while, since my first semester of physics ended. It's not a homework problem, just something I've been doing for fun. I've spoken with a few people about it and they all say it's just a diff. equation but they can't remember how to solve it, and...
  36. N

    If photons don't have mass, why do their paths bend in a gravitational field?

    If photons don't have mass, why do their paths "bend" in a gravitational field? This is question #8 in the FAQ and the answer provided is this: I'm trying to understand the last sentence. I must be having a mental block: why would thinking of "relativistic mass" cause identical...
  37. C

    Investigating Weak Gravitational Field in India/Indian Ocean

    Anyone know what causes the weak gravitation field at the bottom of India / Indian Ocean (see link below)? Thanks http://news.bbc.co.uk/2/hi/science/nature/8767763.stm
  38. C

    Clock in isotropic gravitational field

    1. How would clock in isotropic gravitational field, for example at centre of earth, tick compared to the clock at surface of earth? 2. How would clock in the center of Earth tick compared to the clock at center of sun?
  39. C

    What is the gravitational field ?

    I have read the papers of Verlinde, Jacobson, Beckenstein, Smoot and many other. They use the Unruh vacuum. It seems that Unruh vacuum is nothing but a thermal vacuum in the sense of thermodynamics. It contains vacuum fluctuations creating the virtual particle-antiparticle pairs. Verlinde wrote...
  40. Z

    Gravitational Field & Light Speed: Is Time a Scalar Quantity?

    The speed of light in a gravitational field is not a scalar quantity because at any given coordinate its speed is a function of its direction. Does general relativity treat time in a gravitational field as a scalar quantity?
  41. X

    Gravitational field strength unit

    What quantity has the same numerical value as the gravitational field strength, but is expressed in a different unit? g= 9.8 N/kg i can't think of anything else that's 9.8 besides g
  42. C

    Measuring gravitational field on another plane with a pendulum

    Homework Statement An astronaut arrives at a new planet, and gets out his simple device to determine the gravitational acceleration there. Prior to this arrival, he noted that the radius of the planet was 7040 km. If his 0.400-m-long pendulum has a period of 1.0 s, what is the mass of the...
  43. U

    Circular Motion in SR/weak gravitational field limit

    This scenerio originated from https://www.physicsforums.com/showthread.php?t=391796 where is was intended to argue that in the weak field limit where Newtonian gravity is a good approximation gravitational mass is gamma*m0=E/c2, as opposed to the rest mass argued for by several in that...
  44. U

    Energy of the gravitational field in GR

    I have always thought that GR was identical to classical physics in the Newtonian limit. In the Newtonian limit one can define an energy density for a gravitational field parallel to the methods used to derive the energy density of a static electric field, resulting in a formula energy...
  45. N

    Where Is Zero Gravity Between Earth and Moon?

    Where on an imaginary gravitational field line between Earth and moon, a mass would have no weight neither due Earth nor due to moon?
  46. S

    Combined gravitational field strength

    Homework Statement 2 masses, 5k and 10kg are fixed in place at the coordinates 1,0 and 1,1 respectively. what combined gravitational field strength do they produce at the point 0,0? Homework Equations g = GM/r^2 The Attempt at a Solution total g = G(5)/(1)^2 +G(5)/2 not the right answer...
  47. Z

    Gravitational field strength at latitude

    This figure is captured from my physics textbook and it is about the gravity at latitude http://pix.gogobox.com.tw/out.php?i=567045_.JPG I want to know the difference between mg0 and mg(theta). Which one is the weight of the object? Thank you!
  48. H

    Evaluate the magnitude of the gravitational field at the surface of the planet

    Homework Statement The trajectory of a rock thrown from a height with an initial speed of 16.9 m/s is shown in the figure below. Evaluate the magnitude of the gravitational field at the surface of the planet. The planet has no atmosphere. The graph is as follow...
  49. C

    Photons and gravitational field

    Can the B field of a photon be affected by the gravitational field of another photon?
  50. E

    Gravitational field of photons

    According to L. Susskind in his GR lecture series, a photon has a gravitational field around it. This is intuitive to me as well. The photon has energy, therefore it curves space-time. I have searched, but I cannot find any sources which discuss the nature of the field. If we call the x-axis...
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