# Questions tagged [newtonian-gravity]

This tag is for the questions regarding to the Newtonian model of gravity in which the force between two objects is given by $~GMm/r^2~.$ it is a natural phenomenon by which all things with mass or energy-including planets, stars, galaxies, and even light-are brought toward (or gravitate toward) one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

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### Anomalous calculation about stellar collision

Suppose two bodies of mass $m$, one of them is fixed and the another is free to move,they are separated by a distance $l$ initially and the system is at rest. What would be the speed of the free body ...
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### Question on the decaying elliptical orbit of a comet, causing it to impact the earth

Is it theoretically possible for a comet, in an eighty-year elliptical orbit around the earth, to change trajectory due to a friction-like mechanism, resulting in orbital decay that will impact the ...
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### When is replacing two bodies with a single one at the centre of mass valid?

Two bodies of mass $m$ and $2m$(represented as mm) are in a circular orbit around a large body of mass $M$. The radius of $M$ is $R$ and the radius of the circular orbit of $m$ and $2m$ is $2R$. The ...
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### What distance must two objects have between them in order for them to combine their gravitational field? [closed]

What distance must two objects have between them in order for them to combine their gravitational field? This is Gravity
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### Closed-form solution in Euler's three-body problem and generalization of it

Euler's three-body problem has a closed-form solution, but I cannot find it for it, but I've only found the equation for potential energy. What is the closed-form solution for the $x$- and $y$-...
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### Why charges don't lose potential in a resistance free loop?

If a battery to a current was like the gravity to a massive object, so the potential rise in the battery is like lifting the massive object above earth's surface, so when charges get closer to the ...
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### Gravity affects neutrons

A long time ago I asked whether gravity affected subatomic particles. An experimental physicist kindly explained that it's known to affect neutrons. Get a neutron source, and send a beam of neutrons ...
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### What is the gravitational force acting on a massless body?

It's a well known fact that acceleration due to gravity is independent of the mass of the accelerating body, and only depends on the mass of the body it is accelerating towards and the distance from ...
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### Why are the orbit of planets usually ellipses? [duplicate]

There has been a similar question about planets' orbits being ellipses but the answer circulates around how the circle is a special type of orbit which doesn't really answer my question. Elaborate ...
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### Is friction equal to gravitational force during rolling down a ramp?

I'm studying the motion and forces involved in a ball (bidimensional) rolling down a ramp inclined by an angle $\theta$ from the x-axis. This is the body diagram (I didn't draw forces but there is ...
1 vote
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### Can a rocket be taken to the edge of space with balloons so it can fly from there? [duplicate]

Can we have a (I assume very large) airship or balloon to take a rocket ship all the way to the upper atmosphere so it can use a lot less fuel from there to go to space/other planets. We could even ...
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### Gravitational Potential of a Slowly Spinning Planet

I'm working on a problem in Thorne & Blandford's Modern Classical Physics regarding the shape of a constant density, spinning planet (Exercise 13.5). It asks you to argue that the gravitational ...
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### Work done by gravitation on a system of two-body particles

Suppose we have two planets of masses $m_1$ and $m_2$ and of same radius $r$ kept a distance $d$.Owing to their gravitational force they both move and collide with each other. The system has undergone ...
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### Why is the Moon's gravity so high compared to its mass?

According to Wikipedia the Moon's mass is about 1.23% of Earth's but its gravity is 0.1654g, or 16.5%. If gravity is proportional to mass, why isn't the Moon's gravity 1.23% of Earth's? EDIT: ...
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### Rule of thumb for estimating settling of colloid particles based on size vs $g$ force?

It is generally accepted that once undissolved particles in a solution see one of their dimensions fall below ~1 mcm zeta potential makes them reppel each other more than gravity helps them coagulate ...
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### Could gravity be used to cool down matter?

Thermal energy being the movements of particles, could we have a system that could use gravity to reduce the thermal energy of particles? For example, if we imagine: A box containing Argon in its ...
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### Is the total gravitational energy in the sun greater than the energy that is produced by the sum total of the nuclear fusion contained therein?

I think this is off topic, maybe an astronomy question. Unlike a chemical chain reaction or a fission chain reaction I believe fusion cannot sustain inself. Is more energy going out than is going in ...
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### Orbital velocity of a star

I am supposed to show that the orbital speed of a star is proportional with $\sqrt{r}$, where $r$ is the distance from the center of a galaxy. Suppose the galaxy's mass is equally distributed like in ...
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### Gravitational potential energy inside of a solid sphere [duplicate]

I am self-studying classical mechanics. I came across a problem which required me to calculate the gravitational potential inside of a sphere. I found in one of my textbooks that the potential energy ...
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### Bullet thought experiment continuation

So I'm sure a lot of you have heard the thought experiment where you shoot a bullet parallel to the ground, and drop a bullet at the same time and they hit the ground at the same time. Imagine now you ...
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### Trying to understand gravitational force equation

I don't understand the red underlined equations but I understand gravitational force equation in simpler form. Can anyone please explain the equations? Source An Introduction to Celestial Mechanics by ...
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### How come Newton's universal law of gravitation also leads to negative solution for the distance $r$?

So Newton's universal law of gravitation is: $$F = GMm/r^2.$$ However, if I wanted to solve for distance using Newton's law of gravitation, the equation would be: $$r^2 = GMm/F.$$ Thus if I wanted to ...
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### How do you find the distance between a massive object and its certain gravitational force?

Okay so I know I might've not phrased the question very well so I will give an example to try to make sense of it: Say we have the moon and a place in space where the moon's gravitational force is 1,...
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### How to generate a closed orbit of celestial objects

I'm creating an orbit simulator and my planet is moving in odd elliptical orbits that aren't closed. First of all, is this even correct? Second of all, even if it is, how must I change the parameters ...
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### Robotic arm 'Canadarm' in space that doesn't work on earth

The mechanical arm on the space shuttle, or what's called the Canadarm, can handle a 2200-kg satellite but, on the ground, it cannot support its own weight (Resnick, Halliday). Why is this? What I am ...
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### Solution of the two-body problem

I'm self-studying Lagrangian Mechanics using Goldstein's Classical Mechanics, supplemented with Lemos's Analytical Mechanics, a modern version of the same, and Landau and Lifshitz's Mechanics. ...
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### Gravitational potential at instant of collision

Two spheres colliding that are gravitationally attracted. I want to understand what the gravitational potential between the two is at the point of collision. Is it negative or positive or zero? This ...
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