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

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29 views

Gravity's tall box with a ball inside - scenario

Let's imagine we put a ball inside a box such that it doesn't touch its walls, and suddenly drop the box. Because the two objects fall at the same rate of acceleration, the ball will stay at the same ...
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3answers
60 views

What is the definition of potential energy? [duplicate]

I have problems with this equation: $$U_G ~=~ G\frac{m_1m_2}{r}.$$ It's for potential energy of say something placed on Earth. But it intrigues me. $r$ is the distance from the very center of the ...
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1answer
40 views

When will a ball running between two downwards slopes stop going back and forth?

Two angles $a$ and $b$ meet at a point, making an angle $c$ between them. $a$ and $b$ are all $0 < \theta < π/2$. $c$ is $π/2 < \theta < π$ $a$ is to the left and opens to the left, $b$ ...
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3answers
733 views

Can a building get taller at night?

UberFacts recently tweeted "Office buildings are taller at night—a 1,300-foot-tall skyscraper shrinks about 1.5 millimeters under the weight of 50,000 occupants." Is what they are saying valid? It ...
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1answer
64 views

How does a planet's size really affect its surface gravity?

If we located an exoplanet whose diameter was $x$ times that of the Earth's in size, and which for simplicity appeared to have an identical composition to that of Earth, then its mass might be taken ...
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2answers
52 views

Gravity underground on the moon?

They say that gravity Decreases as we dig into the earth. But I also read that gravity increases for the first approx. 2000km of distance underground. Using this rational, could we dig about 200 to ...
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1answer
116 views

Why are tidal forces pointing away from the Moon?

I am currently reading The Science of Insterstellar, which explains most things very well, but some things leave me confuzzled, which I hope to get answers to here. I am no physicist, but highly ...
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1answer
30 views

What velocity do I need to get the moons orbit perfectly aligned with the earths center [closed]

I have a simulation for universal gravity with two objects. How can I calculate the velocity or instantaneous force I would need to apply to object 2 (the moon) to get it to orbit so that the origin ...
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2answers
70 views

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
64 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
66 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
383 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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2answers
34 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
27 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
45 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 ...
4
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4answers
126 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
120 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
59 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
34 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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6answers
5k views

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
30 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 ...
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1answer
46 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
67 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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0answers
47 views

How much wind power is needed to lift someone up? [duplicate]

I'm talking about fan wind power. A range would be sensible from about 8yrs-50yrs as not all human beings are the same weight with the added weight of a 5kg engine and average skateboard.
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56 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
108 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
311 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
159 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
39 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
62 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
94 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
53 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
113 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
27 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
100 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
45 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
42 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
61 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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1answer
26 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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2answers
43 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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2answers
346 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
34 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
36 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
62 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
33 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 ...
2
votes
3answers
1k views

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 ...