Read about gravitation | 129 Discussions | Page 1

  1. M

    Circular Motion & Gravitation

    Using Kepler's Formula, I tried to solve for the answer but was told that it's incorrect.
  2. O

    I Rosetta orbits and phase space

    I was recently working on the two body problem and what I can say about solutions without solving the differential equation. There I came across a problem: Lets consider the Kepler problem (the two body problem with potential ~1/r^2). If I use lagrangian mechanics, I get two differential...
  3. P

    Time period of flight

    So my doubt is at the beginning of the problems hey are saying that the ball obeys stokes law and on the latter part of the question they are saying that no buoyant force is acting then how does the velocity of the ball change in the end? Also what is the use of specifying 'the ball never...
  4. P

    Pressure inside a sphere

    So I already have a solution available to this problem and the link for the solution is: I have understood everything in the video except the part where they are equating the force dF=GM/r²*dm According to my reasoning the inner part of the sphere (the part below the dm element we have taken)...
  5. Hamiltonian299792458

    B A thought experiment about the Sun vanishing

    suppose suddenly the sun disappears at a time t. at this arbitrary time t, the earth should fling off tangentially to the point in its orbit at time t as there is no centripetal force keeping it in orbit. we know light takes about 8 minutes to reach the earth. so will humans on earth experience...
  6. tanaygupta2000

    Time taken to reach the centre

    The value of acceleration due to gravity at a depth 'd' inside the earth is given by- g' = g(1 - d/R) which can also be written as g' = g(x/R) from the diagram so that x'' = (w2)x where w2 = g/R is the angular frequency Hence the time period T is given by T = 2π sqrt(R/g) but the question...
  7. G

    Determining the power of frictional force

    I can say that the frictional force always against the rolling sphere and the velocity is increasing for the ball. So The dot product F.v keeps on getting more and more negative, so how can the Pf remain constant? Well the velocity increases along the incline and the force of gravity is down...
  8. cianfa72

    I Gravitational time dilatation and curved spacetime - follow up

    Hi, starting from this very interesting thread I'm still a bit confused about the conclusions. The main point, as far as I can understand, is all about conditions for a quadrilateral to be considered a parallelogram. My first basic doubt is: the concept of 'parallel' applies just to geodesic...
  9. A

    Find the attractive force of gravity between two objects

    Homework Statement: Henry Cavendish succeeded in measuring the value of the constant "G" way back in the late 1700s. His method was to put two known masses at a known distance and measure the attractive force between them; then he could use Newton's Law of Universal Gravitation to find "G"...
  10. S

    Gravitation (planetary motion)

    Homework Statement: The particle is moving in circular orbit such a way that the net force (F) is always towards the point p (point p is on the circumference of circle). Find the variation of force F with respect to r. i.e find the value of n in the expression F=kr^n Homework Equations: F=kr^n...
  11. avnl

    A Calculating the propagator of a Spin-2 field

    Nieuwenhuizen uses a method for calculating the propagator by decomposing the field ## h_{\mu\nu}, ## first into symmetric part ## \varphi_{\mu\nu} ## and antisymmetric part ## \psi_{\mu\nu} ##, and then by a spin decomposition using projector operators. Using this he writes the dynamical...
  12. caters

    What is the period of this binary orbit?

    Okay, so let's simplify things and look at the ideal case, where the 2 masses are the same. Well, this gives us a sine wave pattern to the orbital velocity. Consequently, the acceleration would follow a cosine wave since the derivative of velocity is acceleration and the derivative of sine is...
  13. B

    I Issue With Derivation of Gravitational Time Dilation

    Why do we use the equation ##\frac {1}{2}mv^2 = \frac {GmM}{r}## to derive potential velocity, and then put that in the Lorentz factor in order to derive gravitational time dilation? Shouldn't we be using the relativistic definition of kinetic energy -> ##mc^2(\gamma - 1)## to derive the...
  14. D

    I Does dropping a Jupiter from the Pisa tower still accelerate at g = 9.81?

    im confused about this thing, because they said earths acceleration due to gravity is independent from the mass of the thing dropped
  15. R

    Space elevator minimum initial speed

    Homework Statement In the far future, humans have built a space elevator as a cheap means of access to space. However before that could be done, a few basic principles had to be worked out. . . a) What is the minimum initial speed (in an Earth-centered inertial reference frame) needed for an...
  16. R

    Impossible hydrostatic scenario

    Homework Statement There is an infnite high hydrostatic head in an infite high tank on the surface of earth. How big is the pressure p(r) in tank at a distance r. Ignore the rotation of the earth and assume the water stays liquid. ( So basically ignore it's an impossible scenario )...
  17. E

    I Why does mass/energy have inertia?

    I have been googling this topic for some time, but I still don't know if this is still an unsolved mystery of physics (it's just so) or if there is a deeper underlying theory. I get the idea that mass/energy distorts spacetime, justified by thought experiments with moving objects and photons...
  18. AntSC

    B Modifying Newton's Kinematic Equations for High Altitude

    I recently watched a video on youtube where a guy fires a 50 cal. rifle straight up into the air and measures the time of flight at about 100s. It got me thinking about what altitude the round reached. So I used the kinematics equations and obtained a value of 12.25km. Amazing, but I wondered...
  19. Urmi

    Gravitation sum related to Centripetal Acceleration

    Homework Statement The distance between the centres of the earth and the moon is 60 times the radius of the earth. Calculate the centripetal acceleration of the moon. Acceleration due to gravity on the Earth's surface is 10m/s. Homework Equations Centripetal acceleration= v^2/R Orbital...
  20. Pratik Saha

    Gravitational Potential Reference Point

    Can someone please show that calculation of gravitational potential energy at a point R+h from the centre of the earth by choosing the centre of the earth to be at zero potential. Here R is the radius of the earth and h is not very small wrt to R
  21. T

    I Dropped objects hitting the ground at the same time?

    okay, so I’ve had this random thought. We have all been told that objects fall to the ground at the same speed, even if they have different masses. While it’s true that any two objects, regardless of mass, will accelerate towards Earth at the same speed, that doesn’t mean the Earth is...
  22. T

    Integration over a ball

    Homework Statement I'm working on a generalization of gravitation to n dimensions. I'm trying to compute gravitational attraction experienced by a point mass y due to a uniform mass distribution throughout a ball of radius a -- B(0, a). Homework Equations 3. The Attempt at a Solution [/B]...
  23. Rifat amin

    Planets sharing an orbit

    can two planets share the same orbit
  24. J

    Deriving gravitational potential energy -- mistake

    Homework Statement Hi I'm attempting to derive the gravitational potential energy of a point mass (##m##) that's moving from infinity to a point r' inside a gravitational field produced by a another mass ##M##. For simplicity I treated it as a one dimensional case. The problem I get is that the...
  25. A

    Bound stellar system

    Homework Statement A binary stellar system is made of one star with ##M_1=15{M}_\odot## and a second star with ##M_2=10{M}_\odot## revolving around circular orbits at a relative distance of ##d=0.001pc##. At some point ##M_1## explodes in a supernovae leaving a neutron star of mass...
  26. E

    How do write the force diagram for the following situation?

    Homework Statement We have a crate sitting on a scale that is on the surface of the Earth. We want to come up with the value of the acceleration due to gravity, ## g ##, when we take into consideration the rotation of the Earth. Homework Equations In the book, here's how they go about this...
  27. A

    Binary system of stars (##\alpha## - centauri)

    Homework Statement ##\alpha##-Centuary is in a binary visual system with another star. Their separation, from their CM, is 8.0'' and 9.7''. The distance from the Earth is 1.31pc. Their revolution period around the CM is 80.1 years. I have to find masses and luminosities for each star. Homework...
  28. Glurth

    I Self-gravitating ball of gas

    I have a simulation I'm trying out (for fun). A self-gravitating ball of gas, in deep space. (The sim uses a fixed-time-step for each iteration.) I'd like to use Boyles Ideal gas law, the force of gravity, and energy as internal heat. (I don't want to touch enthalpy unless I don't realize...
  29. V

    Gravitation and a Pendulum

    Homework Statement A pendulum having a bob of mass ##m## is hanging in a ship sailing along the equator from east to west. If the ship sails at speed v what is the tension in the string?. Angular speed of earth's rotation is ## \omega ## and radius of the earth is ## R ## Homework Equations...
  30. Pushoam

    Change in the potential energy of a star after explosion

    Homework Statement Homework Equations The Attempt at a Solution I think : the question means that almost all of the potential energy gets used into the explosion. If this is true then the potential energy gets reduced by ## \frac { GM^2} R ## or if the star just gets transformed into a...
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