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Questions tagged [newtonian-gravity]

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

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How do you determine the path of a particle placed in a vector field?

I have recently found a way of expressing newtonian gravity as a vector feild. First the Equation $$F=\frac{Gm_1m_2}{r^2}$$ I only want to know the accelleration in the equation since I only want to ...
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1answer
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What imparts the linear motion or the tangential velocity to natural satellites like the moon to enable them to be in orbit around the earth?

From Newton's laws of motion & gravitation, it is clear that the force of gravitation provides the necessary centripetal force which acts along the line joining the centre of masses of the earth &...
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3answers
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Kepler's 3rd law: ratios don't fit data

I have been looking at satellite orbits around the earth, or any object around any planet in fact, and am trying to find the orbital radius, or semi major length of a given satellite. Kepler's third ...
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Why does the Earth not fall towards the Sun? [duplicate]

According to http://wtamu.edu/~cbaird/sq/mobile/2013/07/01/why-doesnt-the-earth-fall-down/ , the earth does not fall down because of the gravitational force of the sun. At the same time , earth's ...
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5answers
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If F(action) =F(reaction), why doesn't a ball bounce to its original height? [duplicate]

This might seem like a very absurd/ridiculous question, but this question suddenly popped on my head a few days ago. Is it that I'm missing something as I haven't reviewed this topic for quite a while?...
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A body is launched at a height of $8R$. Which of the following are correct? [on hold]

a body is launched at a height of $8R$. which of the following are correct? check the image for detailed question and correct answer and provide detailed solution
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3answers
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Kinematics and dynamics of a crashing satellite

A satellite in low, circular orbit around the Earth experiences drag (friction) and slowly spirals into Earth's atmosphere. It then enters the Earth's atmosphere, heats up catastrophically and burns ...
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3answers
888 views

Inverse square law not accurate for non-point masses?

It would seem that the inverse square law, popularized by Isaac Newton, is only true for masses which have no dimensionality and are a single point. In other words, it is only an ideal, not a ...
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1answer
20 views

Formula manipulation [on hold]

What is the potential energy of a metric ton (1000 kilograms), 3 meters above Earth's surface (at sea level), expressed in Kilowatt Hours? Assume that the mass will end travel when it contacts Earth. ...
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Is Frictional force on each block 3kg or 12kg? [on hold]

Two blocks P and Q of masses m1= 2 kg and m2 = 4 kg are connected to a third block R of mass M as shown in Fig. 3.16 For what maximum value of M will the system be in equilibrium? The frictional force ...
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2answers
62 views

Friction and satellites

There was this question we did in class. There is a satellite orbiting the Earth. It runs into some particles, and due to friction, the satellite loses speed. We were asked to predict what will happen ...
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Gravity and propulsion [on hold]

If a body (m) weighs 200 lbs (90.7185 kg) at sea level and gravity diminishes as the distance between it and the earth (M) increases, what would the body's relative weight be at an altitude of 128,000 ...
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Gravitational potential energy of an isothermal sphere

I am trying to calculate the gravitational potential energy, W, defined as: $W = -\frac{1}{2}\int\rho(r)\Phi(r)d^{3}r$ for an isothermal sphere. I am given that the density profile varies with r as:...
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1answer
32 views

About Kepler's laws [on hold]

Yesterday I was reviewing some calculations using Kepler's laws and when working the third law that relates orbital periods and distances, it is very normal that, given the parameters of some object ...
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6answers
127 views

Acceleration in free fall [duplicate]

A body in free fall "feels" no gravitational force (equivalence). Why does it continue to accelerate. Why is your program refusing my question?
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3answers
68 views

Force due to motion around Sun [on hold]

Think of one person on earth named A . Ignoring Earth for a second, I can imagine him moving around the Sun due to which he should always feel some acceleration towards Sun (Centripetal Force) say F1. ...
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0answers
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Reference Frame conceptual confusion

I am getting confused as to why a ball still feels gravity when inside a moving car. The point of a reference frame is to reinterpret all the forces acting on a particle in one frame only. Hence all ...
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1answer
25 views

Kepler papers (2-body problem) [on hold]

Where can I find papers by Kepler? I am looking for his solution to the two-body problem.
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0answers
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Gravitational potential of an infinite plane

In this link http://www.feynmanlectures.caltech.edu/I_13.html#Ch13-S4 , Feynman first computes the gravitational field generated by an infinite plane of constant density, and then he computes the ...
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1answer
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Nonlinear GPE of a solid block seems wrong

I am trying to calculate the gravitational potential of a solid block, and I have a nonlinear answer which strikes me as wrong. A block with horizontal surface area $A [m^{-2}]$ and uniform density $\...
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2answers
29 views

Would equal balance at same height when hung on a balance?

This is based on a question from the gravitation course on Brilliant. As you can see in the diagram below, we have 2 weights hung on a pulley. It is given that: Neither one accelerates when you let ...
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2answers
42 views

How to find Lagrange point $L_2$ of the Earth-Moon system?

I was tasked in my programming lesson to find a value of L1 correct to 5 significant figures, but in my discussion section I began to wonder why there was no second solution to the equation I was ...
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1answer
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How does orbiting work exactly? [duplicate]

First of all I'm not a physicist or anything and I don't know much about physics, so I'm sorry if this doesn't make sense at all :) And if possible please try to explain it with words instead of ...
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0answers
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Compression of air layer by parallel planes

When object is falling and close to the ground "liquid pillow" appears under it. Object is of cylindrical form. The differential equation that describes the motion is: $$m\frac{dV}{dt} = mg - \frac{...
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1answer
42 views

Which ball touches the ground first? Different explanations

Two balls with the same shape and volume but very different masses are dropped from the same height WITH air. The heavier ball should land first, but is it because of terminal velocity (see this ...
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2answers
68 views

Question About Gravity vs. Earth’s Rotation [duplicate]

If a bullet was fired perfectly straight up (assuming a windless environment) such that the peak of its trajectory was just shy of orbit, would it fall back to Earth in the same spot, or would Earth’s ...
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1answer
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Would a universe with special-relativistic gravity make sense?

Coulomb's law in electrostatics in analogous with Newtonian gravity. It's pretty clear neither of these can be used in a universe that obeys special relativity. They both must be modified to avoid ...
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0answers
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Apple shape with no gravity [closed]

Would the shape of an apple change if it grew with no gravity? I would expect it having a slightly narrower and deeper dent where the stem is attached but I cannot quite figure out how to estimate ...
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2answers
64 views

Does the apple fall towards the earth or does the earth move up to the apple? [duplicate]

Does an apple fall towards the earth or does the earth move towards the earth?...but if this is true then in the opposite side of the world would have to move towards them as well.
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Newtonian Limit of the Accretion Efficiency of a Black Hole

Netzer's book "The Physics and Evolution of Active Galactic Nuclei" (Cambridge) gives, in Section 3.2, the efficiency of a Black Hole (BH) in converting rest mass to electromagnetic radiation as: \...
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0answers
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How to derive the gravitational potential on an infinitely thin disc of finite radius?

I am stuck on a problem that requires me to calculate the gravitational potential on an infinitely thin disc of finite radius $R$ with mass $M$. This infinitely thin disc models a galaxy. Once I have ...
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3answers
148 views

Why is Earth's gravitational acceleration $9.8 \frac{m}{s^2}$? [closed]

How was the value of $g$ determined as 9.8 $\frac{m}{s^2}$? I am not requesting the derivation but the factors/parameters that influence this value.
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2answers
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Gravity below Earth's surface [duplicate]

Why is gravity reduced if you go below earth surface? Asked and answered before but I do not agree with the concepts followed in several answers. The concept of calculating the gravity attraction ...
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2answers
62 views

If an object in free-fall is moving upward, the object's velocity is decreasing. Does this mean that the acceleration is -9.8 m/s/s?

I have a problem (that I am not asking you to solve) where it takes $4s$ for an object to travel upward to its maximum height, and we have to determine how far the object travelled. If the ...
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1answer
114 views

Why does not dark matter gather and form celestial bodies? [duplicate]

since the only thing we know about dark matter that it "attracts" and affect our Baryonic matter's momentum and speed, which means that it does have mass of a sort. so why didn't we witness a ...
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0answers
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How to remove gravity component from accelerometer X,Y,Z reading - 3D space [duplicate]

I'm working with Arduino & MPU-6050 i have read the aX,aY,aZ respectively acceleration in X,Y,Z axis . I have roll, pitch, yaw too. Now I can to calculate acceleration removing gravity component. ...
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4answers
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Rocket Leaving Earth's Gravitational Field

I stumbled across this seemingly simple question that really stumped me on further thought: A rocket is intended to leave the Earth's gravitational field. The fuel in its main engine is a little ...
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2answers
152 views

Why the time period of pendulum with infinite length is $84.6$ minutes? [closed]

In a book I was reading about SHM it stated: If the length of a simple pendulum is increased to such an extent that $\ell\to\infty$, then its time period is given by, $$T=2\pi\sqrt\frac{R}{g}\...
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2answers
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Why do people not have gravitational attraction? [closed]

Gravitational theory says every thing that has mass attract each other. So why don't people attract each other and overlap
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1answer
49 views

Dynamically changing acceleration of object moving towards sun due to gravity

For a collection of sci-fi short stories set in the rather near future I need an approximation of the time it would take a space ship to travel from an Earth orbit to Ceres. In a previous story of ...
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3answers
76 views

Potential energy of an oscillating pendulum

The following question always confuses me. for an oscillating pendulum why the potential energy is given by: $$V = mgL(1-\cos\theta)$$ Why not $$V = mgL\cos\theta$$ Is this a convention or there ...
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2answers
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Free fall ellipse or parabola?

Herbert Spencer somewhere says that the parabola of a ballistic object is actually a portion of an ellipse that is indistinguishable from a parabola--is that true? It would seem plausible since ...
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1answer
63 views

How did Newton use his theory without the value of $G$? [duplicate]

I know that Newton extensively used his theory of gravity to calculate many things, but how did he do so without actually knowing the value of the gravitational constant $G$? Did he estimate it ...
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0answers
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Gravity and Newton's Second Law of Motion [duplicate]

So we were learning about Newton's 3 Laws of Motion and I had a question about the second law and gravity. Newton's 2nd law shows that, with a constant force, if an object has a greater mass, it will ...
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4answers
68 views

Potential Energy in conservation of energy [closed]

In energy conservation theorem, everywhere $PE=mgh$ is used. What I found is that change in PE= mgh. According to me, while calculating total energy, instead of change in PE, total PE should be used ...
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1answer
86 views

State of $N$-body system after time $t$ (under gravity and inelastic collision)

Given the centers of gravity of $n$ spherical bodies of unit mass, $p_1$, $p_2$, ...$p_n$, and assuming perfectly inelastic collisions, how does one find the location of the bodies after time $t$? ...
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0answers
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$N$-body gravity simulator: why does energy conservation break down when introducing an adaptive timestep?

I am playing with an N-body gravity simulator using the velocity-verlet algorithm. In the actual simulation I normalize everything so that it is nicely behaved numerically, but I'll express things in ...
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2answers
39 views

Work done against gravity in climbing and partially descending a wall

A question I found in a book recently concerned two worms climbing up one side of a wall and back down the other side, such that the worms were each half across the wall (I.e. the lengths on either ...
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0answers
23 views

Time interval to closest approach between two sattelites [closed]

Two artificial satellites are in circular earth orbits in the same plane. The orbit radius of one of the satellite is $r$ and that of the other is slightly greater than the other i.e $r + \Delta r$. ...
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2answers
49 views

Why do planets revolve around Sun in elliptical orbits? [duplicate]

Let’s consider two planets of mass $m$ and $M$. They both will attract one another with a constant force $F$ according to the law of attraction $F=G m M/r^2$. The force and masses are constant. $G$ is ...