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

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Question about gravity felt at various radii within a massive sphere

Imagine there's a sphere of radius $R$ which has constant density $\rho$ and you can stand anywhere inside of the sphere. Wherever you stand within the sphere, you'll only feel gravity coming from the ...
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1answer
138 views

Motion in a central field and angular momentum

Is it correct that for a motion in a central force field, e.g. a gravitational field, the absolute value of the total angular momentum of the particle and the component of the perpendicular to the ...
0
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1answer
78 views

Combine forces (gravity)

I have a point at which there are (at least) two different forces (gravity to be precise) working. How do I combine those so that the force acting on the point are as realistic as possible? To put ...
-1
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2answers
134 views

Galaxy rotation equation problem

I would like to know if in this equation for the rotation of galaxies: $$v^2=\frac{GM}r.$$ Is $M$ the mass of the black hole at the center of our galaxy? Someone said to me that No, $M$ is the ...
1
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1answer
218 views

Thought experiment-shell theorem

Consider a uniformly dense perfectly spherical planet. At any point inside the planet, the gravitational attraction is only due to the mass below the point. (red circle) according to shell theorem. ...
-1
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2answers
55 views

Does a 27 hp engine output the same amount of energy as lifting a 1 ton stoneblock almost 3 meters per second? [duplicate]

I'm trying to get a sense of how much energy a $27$ horsepower engine outputs. $$27 \mathrm{hp} = 20133\mathrm{W}$$ Potential energy can be calculated as $$E = mgh$$ where $g ...
0
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2answers
207 views

Escape Velocity (Rail gun, acceleration, weight)

I'm not so technical and not very good with physics, but have some idea based on observation and I believe it is doable. As everyone know also this subject was repeated many times in here, Sending ...
14
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2answers
340 views

Newtonian gravity from the holographic principle?

Can one understand Newton's law of gravitation using the holographic principle (or does such reasoning just amount to dimensional analysis)? Following an argument similar to one given by Erik ...
5
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2answers
1k views

What would a person experience in a free-falling elevator in a shaft long enough to reach terminal velocity?

Assume we had an elevator shaft long enough for a free-falling elevator to reach terminal velocity. As I understand it, when the elevator begins to fall a person inside would experiences ...
1
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1answer
58 views

Newtonian approximation in cosmology

In Peeble's "Large scale structure of the Universe" the Newtonian approximation in cosmology is examined by looking at a transformation that makes the metric locally Minkowski. On pg 38 it is stated ...
16
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5answers
930 views

Does a magnetically suspended frog feel weightless?

Magnetic levitation has been used to suspend frogs in midair. I was wondering: Does the animal still feel gravitational pull? I mean: Does the frog feel like an astronaut on the ISS, or does he feel ...
0
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2answers
75 views

Possibility of low-radius orbit?

Please bear with me, as I'm not in the field of physics, this question may seem a bit simple. This question is concerning stable circular orbits around celestial bodies. I know the equation relevant ...
0
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3answers
86 views

Is it possible to reach the edge of a room if there isn't any gravitational acceleration?

Consider that a large room(an indoor badminton court) is orbiting the earth with a person floating exactly at its center without any relative initial velocity. Consider that the person has no ...
2
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1answer
126 views

What are the determining factors for the velocity of orbiting bodies?

Please bear with me, as I'm not in the field of physics, this question may seem a bit simple. The scenario is the following; A specific stable orbit radius of a small body, say a satellite, to ...
3
votes
3answers
359 views

Are elliptical orbits really elliptical?

I have wondered for a long time how elliptical orbits can work. It seems awkward for a freely-moving object to come very close to a source of gravity and then return to the exact point where it ...
2
votes
2answers
497 views

Does gravity slow down a horizontally thrown baseball?

I have a simple question: Does gravity slow down a horizontally thrown baseball? Assuming when a baseball is thrown it has a vertical velocity as well, does it slow does the ball? Any help is much ...
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2answers
6k views

Pendulum period of different masses [duplicate]

Why does a larger mass in a pendulum have the same period as a lighter mass? i know it has something to do with gravity and length but how can this be explained in depth? like for example the ...
2
votes
2answers
120 views

Path of Orbital Bodies

I am trying to figure out how to parametrize the path of a body under the influence of gravity from another body, but I am stuck. I have looked at the Wikipedia page on Kepler orbits, but it is ...
4
votes
1answer
1k views

Calculating specific orbital energy, semi-major axis, and orbital period of an orbiting body

Is it possible to calculate the specific orbital energy $ϵ$, the semi-major axis $a$, and the orbital period $T$ (or $P$) without any of them being available to you? The values I do have available to ...
4
votes
1answer
209 views

Understanding the different kinds of mass in gravity

On this site, the Phys.SE question Is there a fundamental reason why gravitational mass is the same as inertial mass? has been asked. See also this Phys.SE question. The 'answer' provided on this ...
0
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3answers
328 views

If kinetic energy is a function of the square of velocity, how can gravitiational acceleration be constant?

Kinetic energy is defined as: \begin{equation} E_k = \frac{mv^2}{2} \end{equation} Because of the squared velocity term in there, the faster you're going, the more energy it takes to further ...
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2answers
1k views

Why doesn't mass of bob affect time period?

Please correct me if I'm going wrong - By the gravitation formula: $F = \frac{G m_1 m_2}{r^2} $, So if the mass of a bob is greater then the torque on it should increase because the Force increased ...
0
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2answers
177 views

Initial velocity of an orbiting object that lands on the planet with zero speed w.r.t the surface

How would you determine what initial velocity $v(r)$ of an object would have to be at some arbitrary point in the vicinity of a planet such that the object will end up on the surface of the planet ...
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votes
1answer
100 views

Has anyone measure the strength of the force of gravity in relation to the molecular bonding? [closed]

It's clear to me that gravity it a function of mass. It is also clear to me that gasses are less affected by gravity. So I'm thinking that there exists a measurable minimum binding distance $d$ ...
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3answers
849 views

SMBC ball bouncing problem

This comes from a Saturday Morning Breakfast Cereal (SMBC) comic with a joke answer. The problem states: A 5 kilogram ball is shot directly right at 20 meters per second from a height of 10 ...
3
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3answers
2k views

What provides the centrifugal force for planets orbiting a star?

this is a question I had when I was a kid. I'm a bit ashamed because I think I am missing out on something very obvious since I have the same question despite almost being an engineer now! From ...
2
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1answer
395 views

What if exactly half the Earth's population jumped at one instant? + Secondary Question

I read somewhere that when you jump, the sole effect caused by your jump on the earth moves it about $10^{-18}m$ (I don't remember the figure exactly, but I think it was that). However - obviously ...
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5answers
1k views

What are the forces acting between two air bubbles in water?

The exact question is Two air bubbles in water attract each other repel each other do not exert any force on each other may attract or repel depending upon the distance between ...
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votes
1answer
92 views

Force-Weight Pinewood Derby Car [closed]

Force-Weight Pinewood Derby Car. I'm trying to make a fast derby car. I was wondering if I could make a car that can drop/eject weight once it comes off of the incline. Would that increase speed or ...
1
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2answers
588 views

Change of orbit with radial impulse

This probably is dumb question, but it has been giving me issues for days. I was thinking about a point of mass m in a circular orbit around a planet. The question is: giving a radial impulse, what ...
11
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4answers
4k views

Why don't planets have Circular orbits?

This might be a completely wrong question, but this is bothering me since many days ago. Given the mass (Sun) curves the space around it, gravitation is the result of such curved space (Correct me if ...
3
votes
3answers
655 views

Can we apply Schrodinger equation in Newton Gravitational potential and derive the deterministic Newton's gravitation as a special case of it

We know the solutions for wave functions of a an hydrogen atom, and the energy values as given by spectral analysis of radiation emitted by Hydrogen, confirms the possible energy states as predicted ...
2
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2answers
582 views

Can the mass of an orbiting object and the object being orbited be determined by the distance and orbit velocity alone? [duplicate]

This question is the inverse of: "Could an object orbit while moving at twice the speed, but at the same distance, if it had half the mass?" I'm curious about the nature of orbits, but am not well ...
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2answers
177 views

What's the weight of the earth?

What's the weight of the earth? That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either $0$, because there's no net fall toward the sun, so the downward ...
8
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2answers
316 views

rotational oblateness

I am trying to compute the amount of oblateness that is caused by planetary rotation. I picture the force of gravity added to the centrifugal force caused by the rotation of the planet as follows: ...
15
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2answers
916 views

Is Newton's universal gravitational constant the inverse of permittivity of mass in vacuum?

Is it possible to consider Newton's universal gravitational constant, $G$, as inverse of vacuum permittivity of mass? $$\epsilon_m=\frac {1}{4\pi G}$$ if so, then vacuum permeability of mass will ...
0
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1answer
466 views

Gravitational Field from Irregular Object

How does one calculate the gravitational field of an irregularly shaped object? I was thinking specifically of the gravitational field due to a human, and tried to see if modeling a human as an ...
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1answer
106 views

Expressing a force in components [closed]

If there is an object on some ramp, how do I express its weight in terms of vectors orthogonal and parallel to the ramp surface? For example, if the object has a weight $\vec W=m\vec g$, then how do ...
9
votes
1answer
373 views

What are common methods for calculating the time dependency of elliptical orbit?

After playing a game called "Kerbal Space Program" I got interested in orbital mechanics and started messing with simplified calculations to determine $\Delta v$ requirements. In which I compared two ...
3
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4answers
367 views

Does the law of Universal Gravitation apply to every matter?

If I have a big ball of 20,000,000kg and another of 100g, does it mean that the big ball will pull the small ball towards it?
11
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3answers
527 views

Can we disprove Artificial Gravity (like in the movies) with a thought experiment?

Suppose you have a Device that creates an 'artificial gravity' (AG) inside a Box, with these properties: the system does not use inertial forces (like centrifugal force) or a huge mass to create AG ...
0
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0answers
154 views

Does the earth really move round the sun? [duplicate]

Is there really any empirical proof that the earth moves round the sun? I've read simple explanations using mass-gravity relation. But then some questions remain, is gravity a function of mass alone? ...
3
votes
2answers
203 views

Bertrand's theorem

I found in Goldstein's Classical Mechanics that the condition for closed orbits is given by $\frac{d^2 V_{eff}}{dr^2}>0$.(bertrand's theorem). Can somebody explain to me, how this inequality is ...
-1
votes
2answers
561 views

Two balls falling one above the other [closed]

Two balls, first with the mass $m_1$ and the second with the mass $m_2$ are falling from the heigh $h$. Suppose all the collisions are perfectly elastic and do not consider the size of the balls. $m_1 ...
4
votes
5answers
2k views

What happens with the force of gravity when the distance between two objects is 0?

so I had my first approximation to the gravity equation \begin{equation} F=GmM/r^2 \end{equation} and some questions arose that my teacher couldnt respond: if r approximates to 0 with mM being ...
0
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0answers
63 views

What is the equation for Lin-Shu density wave theory?

Lin-Shu density wave theory is a (very good) theory to explain the spiral arm structure of spiral galaxies. Where can I find the equations that underlie this theory? I've seen its computer ...
0
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1answer
167 views

History of Newtons law of gravitation

I have some questions about the history of Newtons law of universal gravitation. Did Newton discover his three laws of motion before he discovered the universal law of gravitation? I know two ...
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2answers
9k views

Why two balls of different mass dropped from the same height falls the ground at the same time? [duplicate]

When two balls of different masses, thrown from equal height they reaches the ground at the same time. Can anyone explain this in terms of laws of Physics(or with mathematical equations)?
0
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1answer
303 views

Calculate magnitude of force acting on some area by falling object

I have simple question: is it possible to calculate magnitude of force acting on some area by falling object? Let's say I have an object with mass $5\text{ kg}$. I drop that object in height 1 ...
-1
votes
1answer
384 views

Newtons Cannon ball problem [closed]

Let's I have a Newton's Cannon ball of 15 kg and want to fire so it will round the earth and back to me. My query is which law can evaluate the speed that cannon ball will revolve round the sun ...