The Newtonian model of gravity in which the force between two objects is given by GMm/r^2.

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A little confusion in the derivation of potential energy of a shell

This is a paragraph and a figure from The Feynman Lectures, He's trying to prove the Shell theorem for gravity: If we rearrange $dm=2\pi y \mu ds$ we obtain $\dfrac{dm}{2\pi yds}=\mu$. In this ...
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1answer
76 views

How do spacecraft gain kinetic energy by passing near planets? [duplicate]

When a a spacecraft like Voyager travels close to Jupiter, it somehow gains kinetic energy. I'm not sure how this energy isn't simply lost again as it moves away from Jupiter. I'm also hoping this ...
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3answers
74 views

How does The work done in going around any path in a gravitational field is zero implies conservation of energy?

In The Feynman Lectures, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable result. It tells us something we did not previously ...
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4answers
424 views

A confusion regarding an example in The Feynman Lectures

In The Feynman Lectures, In the chapter entitled Work and potential energy, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable ...
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2answers
44 views

What conditions would allow planetary-sized objects to collide and remain intact?

I am modeling some off-the-wall scenarios to try out with a game engine. One idea is trying to make a planet where some weird catastrophic incident has creates a funny shaped planet. I'm hoping to ...
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35 views

Using Dynamics to find the Net Force of a object upon two other masses acting upon it [closed]

So, I drew a picture.. We have 3 masses in a triangle, obvious they are all attracted together, yet they ask for the Fnet on B. Overall I can do questions like these in linear, yet when it comes to ...
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0answers
29 views

Would a very long massive rod exhibit a large deviation from Newtonian gravity (specifically a deficit angle rather than 1/r force)?

In General Relativity the metric corresponding to an infinitely long massive rod is flat but with a deficit angle. It exhibits a very large deviation from Newtonian gravity in all regions of space in ...
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1answer
49 views

What would happen if the Earth were hollow?

This is a question of my exam. What would a person experienced if he were put in any point inside the Earth that is hollow (all its mass is concentrated in the surface). Finding the gravitational ...
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4answers
135 views

Calculating how fast a mass needs to travel in order to launch itself from a hill

Today I was driving on a hill side and on the opposite lane this very careless gentleman was traveling at a very high speed on a large truck that I surely thought his truck would of lifted off the ...
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3answers
122 views

A misconception in an application of Newton's laws

When a body is kept in ground, and is at rest, the downward gravitational pull is balanced exactly by the Normal Reaction if we assume the earth to be an inertial frame. But this would mean that any ...
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2answers
66 views

Why does mechanical energy have to equal zero to find escape velocity?

A object orbiting the earth has total mechanical energy equal to \begin{align*} E^{mech} = \frac{1}{2} m v^2 - \frac{GMm}{r} \end{align*} with $M$ the mass of the earth and $r$ the distance. My course ...
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1answer
37 views

Period to calculate the universal gravitational constant

To calculate the torsion constant in Cavendish experiment we need the period of it, so my question is if I need to measure the time the rod with two small spheres takes to do an oscillation (with an ...
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Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
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1answer
64 views

What is the velocity of Sun due to Earth alone?

If Earth and Sun were in a isolated system, will the Earth's motion around Sun will be similar? What will be Sun's and Earth's velocity when Earth is at its aphelion? Please note that it's not a ...
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0answers
31 views

Anomalous orbit of pluto [duplicate]

Can anyone explain, why, like unlike all planets, Pluto does not have a regular orbit? Why does it have an orbit that meets the orbit of Neptune? Why does it never collides with Neptune? Is it ...
2
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1answer
49 views

Spinning rubber ball with equatorial ridge

I have this rubber ball with something like a very slight equatorial ridge (sort of like Saturn's moon Iapetus) which I often spin around on my desk. I keep noticing that no matter the inclination of ...
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1answer
68 views

Deriving gravitational potential energy using vectors

Here is my attempt at derivation: First you must find a vector function for the gravitational force. By the inverse square law, the magnitude of gravitational force between two bodies of mass $m$ ...
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70 views

Can one verify the Earth tide in his yard?

The ocean tide you can see on the coast. But the Earth tide beneath our feet is hardly perceivable. Is there any way to verify it in one's yard?
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3answers
120 views

Is it possible for man to break Earth into 2 parts? [closed]

Many countries have extreme devastating nuclear weapons. Also they have weapons in very large numbers. I want to ask that Is it possible for man to break earth into 2 parts with the help ...
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2answers
327 views

Will Neil Armstrong's moon boot marks really last for thousands of years?

This question concerns the residual heat (if any) contained within the Earth's moon. At the time of the Apollo moon landings, it was widely reported that the boot marks left by the astronauts would ...
3
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1answer
190 views

Feynman Lectures: Why a non-reversible weight lifting machine cannot lift higher that a reversible one?

Consider weight-lifting machines—machines which have the property that they lift one weight by lowering another. Let us also make a hypothesis: that there is no such thing as perpetual motion ...
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1answer
47 views

Differential form of the law of gravitation potential

I have problem understanding transaction (operations and methods applied) for one equation to other equation. It is about gravitational potential. $${\vec F_{grav}=\frac{GMm_{obj}\vec R}{R^3}}$$ If we ...
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3answers
79 views

Deriving escape velocity using centripetal force

Recently started book on gravity and there (not only there, it is correct way) the escape velocity was given as $${v_{esc}=\sqrt{\frac{2GM}{R}}}.$$ I wanted to derive this myself and I decided to use ...
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0answers
43 views

Gravity between Moon and Earth [duplicate]

It's known that the greater the mass the stronger its gravitational force. Hence, Sun's gravity is definitely stronger than Earth's. So the question arises that why does the Moon orbit around the ...
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1answer
103 views

Calculate orbital changes after acceleration

With the vis-viva equation I can calculate the orbital speed at any position on the ellipse. I want to calculate the opposite way. Assume a satellite with an apogee of 600km and a perigee of 400km is ...
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1answer
55 views

Circular orbits in general relativity(GR)

Reading about Schwarzschild geodesics, I found that circular orbits are possible when the effective force $$ F=-\frac{dV}{dr}=-\frac{\mu{c^{2}}}{2r^{4}}\left(r_{s}r^{2}-2a^{2}r+3r_{s}a^{2}\right)=0 ...
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5answers
116 views

How is energy conserved in this scenario?

There are two objects A and B of equal mass (m). They are laying in close proximity to each other. Object A is then moved further from object B, to a distance r. Since there is gravity between these ...
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1answer
28 views

How may one calculate the escape velocity of a binary system at a given radius from the COM?

Apologies if this is a bit general, even some pointers in the right direction would be great (reading material etc.) Given an object of mass $m_3$ travelling outward at speed $v$ from the centre of ...
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2answers
101 views

Is there a mathematical proof show that :$F=G\frac{m_1m_2}{r²}$? [duplicate]

Is there a mathematical proof about The general law of attraction between two point masses $m_1$ and $m_2$ which represented as: $$F=G\frac{m_1m_2}{r²} ,$$where $r$ is the distance between the ...
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0answers
46 views

Vehicle Driving off Cliff (Thelma and Louise movie)

What is the slowest speed at which a vehicle driven off a cliff can clear the cliff without catching its underside between the wheels? In the usual frictionless vacuum, this would appear to depend on ...
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1answer
43 views

How close to the surface of the Sun would one have to be to determine an 'upright' position relative to it's surface?

As we stand upon the surface of the earth we're able to establish a relative 'up' and 'down' direction due to gravitational forces. As we leave the confines of the earths gravitational attraction ...
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2answers
62 views

Deriving the velocity for circular orbital motion

I'm trying to derive the (circular) orbital velocity for a given height from the center of mass of a body, like Earth. First I used the equation of the circle $x^2 + y^2 = r^2$ to get $y = \pm ...
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32 views

Weight vector dependence

Does the weight of a person depend on the number of people or other bodies in say a room? If so,why? Was thinking about it earlier and want to find out from others.
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53 views

Gauss law for gravitational field

Gauss's law is fundamental law of electrostatics. But Can we apply Gauss's law for Gravitational field also?
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373 views

Do the planets really orbit the Sun?

This is a duplicate of this question on Space Exploration.SE. So why would I ask it again here? Read below. The question reads We often say that the planets orbit the Sun, which is usually a ...
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1answer
35 views

Motion of a ball in a tunnel along Earth's diameter [duplicate]

Suppose, a tunnel is made along the diameter of Earth and we drop a ball inside it. How will the ball behave? Please help me in the stand.
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2answers
47 views

How did Newton figure out the law of gravity? [duplicate]

How did Newton figure out the law of gravity? I know there are two other questions answering the same question but I did not understand anything from the answers Is there a third way of knowing how ...
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2answers
65 views

Physical Meaning of Cone used in Conic Section for Orbital Mechanics

Does the polar angle (complement of $\theta$ below) of a cone which intersects a plane to yield a conic section have a physical meaning in orbital mechanics? Note that the angle of incident ...
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0answers
40 views

Elliptical path of planets [duplicate]

Why are the planet's orbits in the form of an ellipse and what is the proof that earth moves in an elliptical path with the sun at its foci? Initially it was thought that earth moved in a circular ...
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3answers
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Are all trajectories parabolic?

I've heard this before, and it makes sense. Is it true? This being: Due to the effects of gravity and inertia, an object in movement not being acted on by any other force will form a parabolic curve ...
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2answers
40 views

If I make a object enter a planet's gravity it hits the surface with huge velocity, where is it gaining k.e. from?

If I make a object enter a planet's gravity range,it hits the surface with huge velocity,where is it gaining k.e. from? If i keep sending more and more heavy things like above and some how harness the ...
0
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3answers
148 views

How often does the earth rotate around the common center of mass with the moon?

I could not find anywhere how long does it take for the earth to rotate around the center of mass of the earth moon system, which is located inside the earth but off-center. And does this motion have ...
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3answers
87 views

Gravitational acceleration

'What is difference between free fall acceleration g and gravitational acceleration a?***a is with subscript g.In my textbook it is written that "free fall acceleration = gravitational acceleration - ...
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56 views

Sphere of electric charge revisited

I am thinking about a sphere of homogeneous charge distribution (see Electric field due to a solid sphere of charge, for example). Here we use a Gaussian surface (blue area) to find the electric ...
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2answers
79 views

Is it possible to apply Newton's equation of gravitation to attractive force between the moon and the ocean? [closed]

Someone was asking me how much force is acting on the waves when the moon is closest to the earth. Of course the first thing I tried to do is apply Newton's equation for universal gravitation $$F = G ...
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0answers
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the torsion balance of the Cavendish experiment

I need to perform the Cavendish experiment and build a torsion balance but I can't find metallic spheres with enought mass so I was thinking about using a pair of dumbbells instead. My question is if ...
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2answers
60 views

Why are L4 and L5 Lagrange points stable as points and not part of a circle?

I read this Phys.SE thread which is similar Why are L4 and L5 lagrangian points stable? but I did not want to necro that thread. It seems that most discussions of a three body problem are presented ...
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1answer
47 views

Would the Hubble Space Telescope be of benefit for optical astronomy at Lagrangian L5 point?

The Hubble Space Telescope will enter a decaying orbit in 2024. This is a physics based question, so I don't want to get into the engineering details more than necessary. Just for background, the ...
23
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2answers
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How do grandfather clocks keep going?

How do grandfather clocks keep going? The pendulum is what makes the clock go. However, the pendulum will slow down due to friction. What energy source keeps the pendulum from eventually stopping?
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4answers
160 views

What is the speed of Newtonian gravity?

I already read this Phys.SE question but my question is different. I'm well aware that the effect of gravity in GR gets transmitted from point to point at the speed of light. But let's ignore GR for ...