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

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Could an object higher than the stationary orbit be returned to the outgoing point on this orbit?

In the question Centrifuge speed of an object higher than a stationary orbit, I asked: Does an object higher than the stationary orbit move slower or faster around the world than the top of a tower ...
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Centrifuge speed of an object higher than a stationary orbit

In the question At what altitude above equator do gravitational and centrifugal forces cancel each other?, I asked how high a tower on the equator has to be such that at its top, gravitational and ...
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2answers
72 views

At what altitude above equator do gravitational and centrifugal forces cancel each other? [on hold]

How high has to be a tower at equator to get on its peak the same - but of course inverted sing - value of gravitational and centrifugal forces?
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1answer
84 views

Why is the gravitational field potential scalar?

On page 48 of Carroll's Spacetime and Geometry he, before introducing "gravity as geometry", discusses the classical Newtonian equation: $F_{g}=-m_{g} \nabla \Phi$ This equation is very straight ...
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Why $r^2$ and not other power of $r$ in mutual force of gravitation?

My book introduces force of gravitation as a non-contact force between two bodies of mass $M_1$ & $M_2$ seperated by $r$ . Then it says it is directly proportional to the product of masses ...
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36 views

Potential due to a Uniform Ring [on hold]

Consider a uniform ring of mass $M$ and radius $a$ (?). I would like to prove that for $r > a$: $$\Phi(r) = \frac{GM}{r} \sum_0^\infty[P_n(0)]^2 \left(\frac{a}{r}\right)^n $$ Where $\Phi(r)$ is ...
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31 views

What is “W external” and “W internal” in Energy conservation law?

When I solve the energy conservation problem, I am confused when I have to make the term positive or negative. For example, someone throws a ball right up to the ground with velocity, $v$. The ball ...
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27 views

2-D Motion Question which is very confusing [on hold]

I am working on the below problem. I am getting the answer as 31.70 meters but it is not right. A stunt man drives a car at a speed of 20 m/s off a 29-m-high cliff. The road leading to the cliff ...
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1answer
68 views

Does Newton's first law apply also to non-newtonian physics?

I think I understand than an example of Newton's first law (intertial frames) would be a single asteroid in vaccum with no other bodies around, a comet in such free space or likewise. Then I think the ...
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1answer
43 views

An alternate approach to find variation of gravitational acceleration with respect to depth of an object in Earth

As we go down the Earth, assuming it to be a uniform sphere abiding only to Newtonian physics, the gravitational acceleration imparted to an object by the Earth goes on decreasing, and decreases to 0 ...
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6answers
76 views

Trouble understanding the concept of true and apparent weight

I need help understanding the concept of true weight vs apparent weight. I understand this much: if someone is standing in an elevator on a scale, the further up they go the less the reading on the ...
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Calculating Centripetal Force Upon Satellite [closed]

A satellite of 150kg orbits Earth over 272km altitude. The diameter of Earth is 12576km. The mass of Earth is 5.967 * 10^24kg. The orbital period of the satellite is 90minutes. By $F = ...
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2answers
60 views

Time for launched object to reach point in space

I am attempting to calculate the time required for an object launched perpendicular to the surface of the earth at escape velocity to reach an arbitrary point in space (neglecting rotational velocity, ...
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0answers
9 views

Is it possible to calculate Lagrangian isolines for local stars?

Is it possible to calculate Lagrangian isolines for local stars? SciFi descriptions of 'hyperspace' always talk about travel routes between the stars following some sort of route. As a thought ...
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1answer
35 views

Calculating $g$-force in between planets

The g-force is given by $1 + \frac{a}{g}$. The question is that a rocket is accelerating from between Mars AND Juptier at 26.95m/s. The astronaut in focus is 60kg (irrelevant I believe). Using this, ...
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1answer
98 views

Is relativistic event horizon half of Newtonian event horizon?

Is Relativistic event horizon half of Newtonian event horizon? relativistic escape velocity formula (from $m\phi=E-E_0$) is $v_e=\sqrt{2\phi-(\frac{\phi}{c})^2}$ and the Newtonian version of the ...
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3answers
105 views

How fast would the Earth need to spin for us to feel weightless?

It's a classic question with many answers all over the Internet, but none here so I figured I'd ask it: How fast would the Earth need to spin for a person (or anything for that matter) to feel ...
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2answers
156 views

Energy to reach the moon

I've been stuck on this question for a couple of days now. Given that the potential energy of a 930 kg object on the Earth's surface is -58.7GJ, calculate the minimum energy required for the 930 ...
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3answers
170 views

Armageddon prevention

I was watching the movie Armageddon and it made me think of a few things. We would probably not need to send a crew to blow the asteroid in two, I think we could still send a warhead with enough power ...
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1answer
29 views

Gravitiation force of a sphere

Was wondering about Shell Theorem, specifically about the immediate results. Force (on a point mass) inside a shell is 0. Force (on a point mass) outside a shell is GmM/r^2 From what i know the ...
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1answer
27 views

What is the simplest way to perform a Cavendish experiment?

The Cavendish experiment is cool, but seems complicated to experimentally perform. What is a simple way to recreate the experiment?
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0answers
10 views

Having trouble reconciling Newtonian-derived earth mass with direct calculation [closed]

Our calculation of Earth's mass as $M_E=5.97\times 10^{24} \:\mathrm{kg}$ is made by observing the gravitational interaction between the moon and the earth and then solving the relation ...
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1answer
33 views

General potential of rotating system

I'm new here at the physics site, and not really that deep into the area of which i'm going to ask a question about now. Therefore please feel free to ask clarifying questions. I'm trying to deal ...
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2answers
80 views

Why are some forces not included in the sum of forces?

I was given the following notes in class: 4.32 A skier of mass $65.0\text{ kg}$ is pulled up a snow-covered slope at constant speed by a tow rope that is parallel to the ground. The ground ...
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17 views

Reason behind the rotation of Earth? [duplicate]

I want to know what is the reason that the Earth rotates on its own axis? What are the forces responsible for the Earth's rotation?
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1answer
73 views

Velocity of satellites greater than required velocity

We often find velocity required to keep a satellite in orbit by the formula $v=\sqrt{\frac{GM}{r}}$ where $v$ is perpendicular to the gravitational force. It is very intuitive that the object will go ...
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1answer
169 views

Giant leap of the space goat

This problem was inspired by this Math.SE post and similar problems involving tethered animals. A space goat is tethered to the north pole of a spherical asteroid of uniform density and radius $a$ ...
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1answer
50 views

Earth-Moon system

While learning about motion of centre of mass, I came across this statement online, It is also more accurate to say that the Earth and Moon together revolve about their common center of mass. ...
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3answers
88 views

Escape velocity of satellites

I know that the equation for it is $$v^2 = \frac{2GM}{r},$$ and with that, the rocket should be launched at that speed. But could it go much slower spending much more fuel to escape from gravity ...
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26 views

Does gravity weaken by the square of the distance because the energy is dispersed over the square of the distance [duplicate]

The area of a circle is $\pi r^2$ if you increase $r$ the area will increase by the square so if this area was of energy and you increase the area it is dispersed you would expect its energy to weaken ...
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5answers
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Is this scene from the A Team explainable by Physics?

This scene (youtube link) from the movie The A-team, the four members are in the tank and its falling from the air, they fire the canon and it slows the tank from falling for a moment before falling ...
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1answer
100 views

How can a planet gravitationally capture objects?

I would expect that any asteroid or other object originating far away but passing near a planet would pick up speed and energy as it approaches, but unless it comes into contact with the atmosphere ...
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2answers
40 views

Projectiles Launched at an Angle with unspecified Initial Velocity [closed]

I'm attempting to do my Physics homework, and I did the first one right, but that problem gave me initial velocity. This problem gives me only the angle relative to horizontal and the distance it ...
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2answers
56 views

How to calculate gravitational force

Suppose the centre of mass of 2 bodies coincide , then how will we calculate the gravitational force between the 2 bodies ??
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Find net force on a mass centered between four other masses

I'm not going to post the full question, I just want a general idea of how I should go about solving this type of problem. There is a square with 4 charged masses on each of the corners, in the ...
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5answers
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Where does the extra kinetic energy come from in a gravitational slingshot?

I read in this answer in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the ...
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Question on acceleration of gravity

In pre-calculus last week my teacher explained a scenario in which a man throws a rock down a well and takes 4 seconds for you to hear the rock hit the bottom. How far downs the well? Last years I ...
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0answers
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Do we weigh less in the morning? [duplicate]

A question on Biology SE got me thinking, ignoring weight naturally lost during the night, "Do we weigh less in the morning?" During the night, the sun is above us, and the earth below us. ...
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5answers
466 views

Why are orbits elliptical? [duplicate]

Just wanted to know why planetary orbits get to be elliptical? I'm not debating how stable these orbits are (obviously almost completely stable), but why don't planets revolve in the special ellipse ...
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28 views

What if there was a hole between earth poles [duplicate]

Imagine if there was a hole between two earth poles, let's say 100 meters wide, as deep as the Earth's height between north and south poles - what would happen if we threw an object from the North ...
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1answer
41 views

Why is gravitational potential energy negative? [duplicate]

Why is gravitational potential energy negative? How is it different from other forms of energy? I recently saw a video by Dr. Michio Kaku, he said that the total energy content of the universe is ...
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1answer
69 views

Advantages/Disadvantages of “hanging off” a motorcycle when leaning

The closest question I could find with regards to this subject was this one: Countersteering a motorcycle However, it does not address the specific physics of what I would like to know. There are 3 ...
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5answers
111 views

Satellite Collision Problem

I'm stuck on a problem of two satellites going towards each other. The mass of the first satellite is 400kg and the mass of the second satellite is 100kg. The altitude of the satellites is 1000km. I ...
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2answers
359 views

How does escape velocity relate to energy and speed?

I have several confusions regarding escape velocity. I am sure I am missing something(s) obvious or maybe I am taught wrong. Lets say we throw an object of any mass at exactly escape velocity of ...
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1answer
46 views

Weight held by jet stream of water

Consider a bucket of weight $W$, held in air by a jet stream of water from the ground (moving vertically upwards) at height $h$. The water is fired from the ground at the rate of $\mu$ (units ...
2
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2answers
604 views

Why doesn't gravity bend everything equally?

If gravity is the curvature of spacetime it should bend everything equally. To clarify my point I would like you to imagine two scenarios. Think of a bird flying in the storm while the wind is blowing ...
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0answers
37 views

What causes the unexpected change in acceleration for flybys of spacecraft?

If the vehicle is not operating on RTG, then thermal recoils of photons shouldn't be considered as in the case of PIONEER. Then what actually accelerate the spacecraft from expected value (expected by ...
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3answers
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Work done by gravity on a ball & the ball on earth

I have studied today that if a ball was to fall a certain height, then the work done by gravity on the ball would equal the work done by the ball's equal and opposite gravitational pull. By $W=Fd$, ...
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1answer
91 views

How far has a black hole to be in order for its tidal forces to disintegrate earth?

I don't know if this question can be answered to honest but I though I might try ask just in case someone can calculate that. What I need to know here is how strong should the tidal forces be to start ...
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A force opposing Gravity

Every Action Has An Equal and Opposite Reaction (Newton's Third Law.) If this is the case, does gravity have an equal-opposing force? From asking around I still haven't got a very clear answer; ...