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. J

    Gravitational Field of Moving, Rotating Globe: A Question

    Consider a solid globe of mass M and of of uniform density. My understanding is that its external gravitational field, in the absence of any other forces, will apply an instantaneous acceleration to any small test mass directly towards the center of the globe. Is that still true in the...
  2. K

    Disk rotating in a gravitational field, like a clock

    Suppose we have a large circular disk with pegs around the perimeter, and we set the disk rotating so that one pegs passes us every second. Then, we move this disk to a gravitational field, such that one side of the disk is closer to the gravitational mass than the other. From our perspective...
  3. pyman999

    What is the mistake in my calculation for gravitational field strength?

    Homework Statement Homework Equations g = GM / r^2, where g is the gravitational field strength, G is the gravitational constant, M is the mass of the attracting body, r is the radius of the attracting body. p = M / v, where p is density and v is the volume. Vs = 4/3 * pi * r^3, where Vs is...
  4. DOTDO

    By what method did Einstein derived his gravitational field equation?

    Hi. In class, the professor has tried to derive the equation by using the principle of least-action. (But not yet completed. Maybe next class...) However I heard this method is used by Hilbert, who had derived the equation 5 days before Einstein derived it. Then, what method did Einstein use...
  5. Ess_Elle

    Meteor Gravitational Field Question

    Homework Statement A 12 kg meteor experiences an acceleration of 7.2 m/s^2 when falling towards the earth. a) How high above the Earth's surface is the meteor? b) What force will a 30 kg meteor experience at the same altitude? Homework Equations Fg= Gm1m2/r2 m1m2 r2 = Gm1m2/Fg r =...
  6. P

    The (non-?) flatness of a uniform gravitational field and the equivalence principle

    Desloge (1989) published the article: ## '##Non-equivalence of a uniformly accelerating reference frame and a frame at rest in a uniform gravitational field## '##. His result, briefly resumed: a uniform gravitational field is not flat, is quite interesting. But the way he proves the result is...
  7. N

    Gravitational Field of a Uniform Rod

    Homework Statement A thin uniform rod of mass M and length L is centered at the origin and lies along the x axis. Find the gravitational field due to the rod at all points on the x-axis in the region Picture adjunct Homework Equations My two question are: Why r is'not the difference between...
  8. Ookke

    Gravitational Fields Created by EM Waves: Reference Frame?

    If EM waves create gravitational field "around" them (as I understand is the case) which reference frame we should use? We could imagine several observers, some moving in the same direction with EM wave with different speeds, others moving in the opposite direction. The different observers...
  9. GhostLoveScore

    Trajectory in gravitational field

    So, I'm attempting to programm orbit in Unity game engine. So I need equation that shows r and phi depending on time. Equation for gravitational potential is U(r)=-k/r+M^2/(2*μ*r^2). Force is -1*derivation of U(r) by r. So I get lots of stupid stuff. If anybody could help me to...
  10. R

    A clock tower puzzle in a gravitational field

    In General Relativity spacetime is described by a metric. The most common one is the Schwarzschild metric, valid at radii greater than the surface radius of a mass. If we assume constant angular position so that dθ=dø=0, then this metric relates local (proper) coordinate time and distance dτ...
  11. WannabeNewton

    1-dimensional polymer in gravitational field

    Homework Statement A rubber band at temperature ##T## is fastened at one end to a peg and supports from its other end a weight ##W##. Assume as a simple microscopic model of the rubber band that it consists of a linked polymer chain of ##N## segments joined end to end; each segment has length...
  12. Quarlep

    Gravitational Field Strength due to a Uniform Rod

    I am trying to learn Physics an dI am reading a booK about classical mechanics.I a stuck somewhere in there If you know a gravitational force to a uniform rod I saw there a x and dx Why we need them ? Thanks!
  13. J

    General equation of motion with gravitational field

    I was studying the equations of free fall and of launch when I realize that those equations are spetial case of a object in motion through of a gravitational field. So exist some general equation that describe the motion (the trajetory*) of the object through of the field (using initial values...
  14. H

    Relationship between gravitational field strength and potential

    Hi, I am a bit confused with the relationship between gravitational field strength and gravitational potential. As far as I know, gravitational field strength is defined as: g=\frac{F}{m}=\frac{GM}{R^{2}} and gravitational potential is defined as: V=\frac{-GM}{R} Now if I...
  15. 3

    The gravitational field at a mass point produced by an infinite plane

    I'm reading: http://www.feynmanlectures.caltech.edu/I_13.html#Ch13-S4 1. In the link it says: ##2\pi\rho d\rho## is the area of the ring of the radius ##\rho## and width ##d\rho##, if ##d\rho \ll \rho##. Why is this true?? 2. A bit further down in the text it says: Since ##r^2 =...
  16. N

    Proper time of an accelerated frame in a external gravitational field

    hi everyone. I'm having trouble understanding the concept of proper time in general relativity. suppose we have some metric given by a fixed mass distribution, say schwarzschild or something (it's not important) and a test particle go over some path between two events A and B. if we want...
  17. H

    Defining negative energy of gravitational field

    I have been learning that gravity has a negative energy associated with it. I've heard this stated a couple different ways, but I would like to understand a distinction. One line of thought declares that the potential energy of an object within a gravitational field is negative. Another line...
  18. P

    Symmetry of gravitational field to electric field and Maxwell equation

    Symmetry is an important way to find new physical laws according to Feynman. The equation that describes the electric field and the gravitational field are quite similar. Since the electric and magnetic fields are well defined by the Maxwell equations could it be possible, by symmetry, that...
  19. A

    E=mc^2 in a gravitational field

    Let us say that we have small object of mass ##m## at some location far away from the Earth (with zero velocity compared to the earth). The energy of this object is according to relativity ##E=mc^2##. Now we drop this object and it starts falling towards the earth, transforming potential...
  20. Q

    What is intuitively the source of the gravitational field?

    In general relativity, the source of the gravitational field is the "stress-energy tensor" I know that thing is not just energy. Can some one explain what this quantity is? It's just a 'thing' that just happens to work mathematically and means nothing else?
  21. Saitama

    What is the most efficient method for solving this gravitational field problem?

    Homework Statement A thin hemispherical shell of mass M and radius R is placed as shown in figure. The magnitude of gravitational field at P due to the hemispherical shell is ##I_0##. The magnitude of gravitational field at Q due to thin hemispherical shell is given by A)##I_0/2##...
  22. O

    Gravitational Potential Energy and Gravitational Field and Gravitation

    I don't get the difference between these equations: U = \dfrac{-Gm_1m_2}{r} F_g = \dfrac{-Gm_1m_2}{r^2} g = \dfrac{F_g}{m} = \dfrac{GM}{r^2} Also, why are the first two negative? Here's my thinking: The first equation is like U=mgh. Except it's when two masses are very far apart. It...
  23. MalachiK

    Drawing a gravitational field inside a planet

    For a point mass acting as a source of a g field we draw lines that point inwards from infinity. Where we have an extended body like a planet, I've always drawn the field lines terminating on the surface. However, I've seen a question in an exam paper that implies that it's okay to continue...
  24. M

    What is Gravitational Field Strength in General Relativity?

    "gravitational field strength" Hi all, I've been reading some lecture notes by G. t'Hooft, available from http://www.staff.science.uu.nl/~hooft101/lectures/genrel_2010.pdf On page 12, t'Hooft is discussing the Rindler space of an observer using co-ordinates \xi^{\mu} with constant...
  25. P

    Kinetic energy loss in a gravitational field.

    If I throw a ball vertically upwards from the surface of the earth, the upward motion slows due to gravity. At the ball's highest point, I have placed a repositioned platform for the ball to rest on; so it sits motionless, perched above the surface of the earth. When the ball began it's...
  26. C

    Free fall trajectory in non constant gravitational field

    Rusty on the math... I am working on a problem and need the derivation of a free fall trajectory for an object at a distance above Earth where the change in acceleration is not negligible. How do I integrate the distance/ acceleration formula taking into account the change in g to get the...
  27. P

    Atomic clocks in gravitational field

    In his paper, Chou et. al., 2010 has demonstrated that an atomic clock at the height of our head ticks faster than an atomic clock at the height of our feet. I was thinking that one electromagnetic process can be substituted with any other - so that corresponding atoms in our head tick faster...
  28. B

    The gravitational field g due to a point

    The gravitational field g due to a point mass M may be obtained by analogy with the electric field by writing an expression for the gravitational force on a test mass, and dividing by the magnitude of the test mass, m. Show that Gauss' law for the gravitational field reads: phi = oint...
  29. B

    Can You Orbit an Asteroid by Running?

    Homework Statement Assume you are agile enough to run across a horizontal surface at 8.50 m/s, independently of the value of the gravitational field. What would be (a) the radius and (b) the mass of an airless spherical asteroid of uniform density 1.10 310 3kg/m3 on which you could launch...
  30. W

    Fast computation of gravitational field level lines

    Homework Statement Dear all, I have to find a fast way to compute changes in the level lines as the result of sudden changes in the local gravitational fields (2D space). (Caused by the destruction of a planet for example). I could recalculate everything but it takes too much time for the...
  31. M

    Freefall in a Newtonian gravitational field

    1) The problem statement : For this problem, We use Newtonian Mechanics. We are placed in a geocentric frame of reference. An object (of which the mass is irrelevant for this problem) is released into the Earth's gravitational field at an altitude p(0) with no velocity whatsoever. The...
  32. T

    Time dilation in gravitational field

    A friend of mine posed the following conundrum: If you have 2 identical clocks one at the top and one at the bottom of a tower (on the earth), then for an observer at the top, the clock at the bottom appears to go more slowly than the clock next to him. This one can deduce from the redshift of...
  33. Q

    Calculating Escape Velocity of Mars from the Sun's gravitational field

    1) The problem: Mars orbits the Sun at a distance of 2.3 * 10^10 m with a speed of 24000 m/s. If it's speed were increased to 30000 m/s, at a time when no other planet was nearby, would Mars leave the Solar System. 2) Fc=Fg Orbit formulas and such 3) I'm assuming you have to find the escape...
  34. I

    Gravitational field strength of 0

    Homework Statement A planet of mass 1.88x10^21 kg has a moon of mass 4.56^10^19 kg. The distance between their centers is 3.94x10^8 m. How far from the center of the planet (along the line joining the planet and the moon) is the net gravitational field strength, due to the two bodies, equal to...
  35. D

    Gravitation equations and expressions - gravitational field strength

    Homework Statement i have 2 questions on my holiday homework that I am not 100% sure on they are: Homework Equations 1) write down an algebraic expression for g at a distance r from the centre of the planet. The planet can be treated as a point mass of magnitude M as its centre AND 2) write...
  36. C

    What happens to the gravitational field strength's magnitude if

    Homework Statement What happens to the gravitational field strength's magnitude if a) r decreases by a factor of 4? b) r increases by factor of 2 Homework Equations i'm not sure which equation they are referring to? it may be g ∝ 1/r^2The Attempt at a Solution I tried to do this: 1/ (r-4)^2...
  37. Z

    Can we extract energy from a gravitational field ?

    hey there MTW mention that the mass energy of the Earth moon system is less than the mass energy that the system would have if the 2 objects were at infinite separation. MTW say that it is due to gravitational forces. Please correct me if I'm wrong : The fact that the moon follows a...
  38. S

    How is acceleration equivalent to rest in a gravitational field

    Let me phrase the entire question: How is acceleration equivalent to rest in a gravitational field (without tidal effects)? It's not that I am incapable understand the implications of this--it comes from a quote by DaleSpam and it seems to be rich--I just cannot break down the language he is...
  39. H

    Gravitational field strength (ratios)

    Homework Statement A 6.2*10^2-kg satellite above Earth's surface experiences a gravitational field strength of magnitude 4.5-N/kg. Knowing the gravitational field strength at Earth's surface and Earth's radius, how far above Earth's surface is the satellite? (Use ratio and proportion.)...
  40. P

    How does matter accelerate in a gravitational field

    I have been reading various forums etc but can't find a clear explanation of how the space-time warping causes an object to accelerate/gain energy. I don't want pseudo explanations about potential energy etc. Thanks
  41. D

    Ideal Bose condensation gas in gravitational field, Statistical Physic

    Homework Statement We have an ideal Bose gas in gravitational field. Show that the critical temperature( the temperature in which the condensation is starting is: T_c = T^0_c( 1 + \frac{8}{9} \frac{1}{ζ(3/2)} (\frac{\pi mgh}{kT^0_c})^{1/2} ) Attempt Lege artis; Firstly I want to...
  42. J

    Equilibrium temperature distribution in gravitational field

    I came across Tolman's paper on the equilibrium distribution of temperature in gravitational field. He argues that in contrast to classical thermodynamics situations, in gravitational field, a fluid in thermodynamic equilibrium will not have the same temperature everywhere (as measured by...
  43. F

    What is the Potential Function and Gravitational Field of Earth?

    I'm sorry if this sounds confusing. But I'm writing this question exactly how it is written in my textbook. I am stumped on this problem: Find the potential function and gravitational field of the earth. Then use those equations to determine the work that must be done to get a 100kg satellite...
  44. V

    Path Calculation of point mass in gravitational field

    Hi, I am trying to derive a formula for the path taken of a body in a Gravitational Field using Classical Mechanics. I have attached a pdf file with my derivation so far. Basically I used conservation of energy and conservation of angular momentum to derive a diferential equation...
  45. sergiokapone

    Homogeneous gravitational field and the geodesic deviation

    In General Relativity (GR), we have the _geodesic deviation equation_ (GDE) $$\tag{1}\frac{D^2\xi^{\alpha}}{d\tau^2}=R^{\alpha}_{\beta\gamma\delta}\frac{dx^{\beta}}{d\tau}\xi^{\gamma}\frac{dx^{\delta}}{d\tau}, $$ see e.g...
  46. W

    What is the strength of the gravitational field?

    Homework Statement What is the strength of the gravitational field on the ground just above the oil deposit? Hint: Consider the missing mass as a sphere with a negative mass. Given: a spherical oil deposit with radius 200m at a centre of depth 2.0km. The density of the Earth's crust is 2700...
  47. C

    Gravitational field strength between masses

    Homework Statement A mass at a point X gives rise to a gravitational field strength g at point P as shown. An identical mass is placed at point Y x ________ p ______________________ y The resultant g f s is now? Homework Equations g = Gm/r2 The Attempt at a Solution...
  48. Negi Magi

    What will the gravitational field inside the Earth be?

    There is a question: If we dig a channel from the North pole of the Earth to the South pole of the Earth, then we release a ball into this channel from the North pole, what will be the motion of this be like? I think this question is related to the inner gravitational field of the Earth
  49. M

    Is relative mass making gravitational field?

    Hello When you have something and it gains a lot of mass m due to its high kinetic energy, so it gains a lot of relative energy. So, every object has its own gravitational field. So is the RELATIVE mass making a gravitatinal field? mathematically if g=GM/Rˇ2 does work, where you MUST add...
  50. F

    Calculate Gravitational Field Strength

    Homework Statement Given Radius is 4.76*10^5 m Astronaut drops a hammer of 0.85kg from a height of 1.25m. It takes 3s to reach the ground What is the gravitational field strength? Homework Equations The Attempt at a Solution g=a=Δv/t v=d/t v=1.25/3 a=1.25/3/3 But that's...
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