# gravitation

1. ### 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"...
2. ### 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...
3. ### 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...
4. ### 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...
5. ### 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...
6. ### 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
7. ### Space elevator minimum initial speed

1. 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...
8. ### Impossible hydrostatic scenario

1. 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 )...
9. ### 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...
10. ### 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...
11. ### Gravitation sum related to Centripetal Acceleration

1. 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. 2. Homework Equations Centripetal acceleration= v^2/R Orbital...
12. ### 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
13. ### 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...
14. ### Integration over a ball

1. 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). 2. Homework Equations 3. The Attempt at a Solution...
15. ### Planets sharing an orbit

can two planets share the same orbit
16. ### Deriving gravitational potential energy -- mistake

1. 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...
17. ### Bound stellar system

1. 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...
18. ### How do write the force diagram for the following situation?

1. 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. 2. Homework Equations In the book, here's how they go...
19. ### Binary system of stars ($\alpha$ - centauri)

1. 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. 2...
20. ### 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...
21. ### Gravitation and a Pendulum

1. 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 $R$ 2. Homework...
22. ### Change in the potential energy of a star after explosion

1. Homework Statement 2. Homework Equations 3. 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...
23. ### Derive Formula for Velocity of Object Approaching Earth

1. Homework Statement A particle of mass m is dropped from a height h, which is not necessarily small compared with the radius of the earth. Show that if air resistance is neglected, the speed of the particle when it reaches the surface of the earth is given by $\sqrt {2gh}$ ##\sqrt {\frac...
24. ### I How does energy source curvature?

TL;DR Why does the Einstein equivalence principle imply that all forms of (non-gravitational) energy source curvature? Now, as understand it, the Einstein equivalence principle (EEP) implies (or at least suggests) that gravity is the manifestation of spacetime curvature, the reason being that...
25. A

### B Telescope and Stopwatch for the Mass of a Planet

I was wondering if it is possible to use only a stopwatch and a telescope to find the mass of a planet, such as Saturn. I've experimented with a couple of things but I keep running into problems. I previously asked this question in the homework section, but it does not involve numbers, is not...
26. A

### Finding the Mass of Saturn

1. Homework Statement Using only a telescope and a stopwatch, find the mass of Saturn. (This question may or may not make any sense at all, it was a theoretical lab that my professor said without giving us a chance to copy it down and I am trying to recall the question from memory) If it is...
27. ### Relativity Is Gravitation by Misner, Throne, Wheeler outdated?

Hi! With the re-release of the textbook "Gravitation" by Misner, Thorne and Wheeler, I was wondering if it is worth buying and if it's outdated. Upon checking the older version at the library, I found that the explanations and visualization techniques in the sections on differential(Riemannian)...
28. A

### Gravitational force acting between objects

1. Homework Statement 4 10kg objects are located at the corners of a rectangle sides 2 meters and 1 meter. Calculate the magnitude of gravitational force on 1 due to the other 3. (Same sort of idea) 3 1kg objects are located at the corners of an equilateral triangle of side length 1 meter 2...
29. ### What should I learn?

Hello, I don't know if this is the right place to post this topic, I could not figure out the right one. I have recently finished my Masters in Condensed Matter. Now I want to follow a PhD where I can work/research on the dynamics of the Universe especially on dark energy, modified gravity...
30. F

### B Does Heat apply Force?

When we heat something then it breaks and it is due to the transfer of energy . But what if we ignore the energy and thought it as Force I.e. the object molecules break due to Force applied on each other ( molecules) . So is it right to say heat apply Force.?