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

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8answers
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Could a “living planet” alter its own trajectory only by changing its shape?

In Stanislaw Lem's novel Solaris the planet is able to correct its own trajectory by some unspecified means. Assuming its momentum and angular momentum is conserved (it doesn't eject or absorb any ...
1
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1answer
31 views

Solar balloon vs hydrogen or helium filled balloon

This is my very first post here and I used the search engine to make sure this set of questions was not asked before. Sorry if it is the case for some reason. Feel free to delete my post. Here are my ...
0
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0answers
29 views

Why does the inverse square law cause elliptical orbits? [duplicate]

I've seen it printed multiple places, here for example, that the reason orbits are elliptical is because the gravitational law has an inverse square of the radius. Why does this make the orbits ...
1
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2answers
90 views

Negative Gravity Fields and Time Dilation [duplicate]

Question: Some physicists believe that it is possible to have negative mass. My questions is would this negative mass create a negative gravity field, exerting a negative force on positive masses? And ...
0
votes
1answer
32 views

Where does gravity get it's energy to cause tides? [duplicate]

The moon's orbital radius is fixed as a function of its velocity (I know it is actually drifting..). Since there is nothing in space to resist this velocity, it will continue orbiting "forever". Now ...
2
votes
2answers
116 views

Equation for a falling body including terminal velocity

I'm making an app that times how long it takes a pebble to fall, then calculates the distance it fell. I noticed that the simple $f(t) = \frac{1}{2}gt^2$ was becoming increasingly inaccurate as the ...
0
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0answers
30 views

Average of the velocity vector along a Keplerian orbit

I would like to show that the average of the velocity vector $\mathbf{v}$ along one Keplerian orbit vanishes, i.e. $$ \frac{1}{2 \pi}\int_{0}^{2 \pi} \!\!\!\! \mathrm{d} M \, \mathbf{v} = \frac{1}{T}\...
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1answer
32 views

Rolling motion of a rigid object

I have the situation described in this picture I know the speed of the ball at the top of the loop ($v_{top} = 2.38 m/s$), and I have to demonstrate that the ball does not fall from the track at ...
5
votes
2answers
146 views

Kepler Orbits: Small Perturbations->Elliptical Orbits

A group of my physics classmates and I have been stuck on this problem. We have tried a few approaches. The problem is to show that a body following a circular orbit, when given a small radial ...
-2
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1answer
53 views

Gravity and angular momentum

When a mass moves towards a bigger mass at a constant velocity, they will be attracted to each other such that the smaller mass will revolve around the bigger mass with the same speed as before. ...
7
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1answer
77 views

Details of Newtonian Prediction for Mercury's Precession

Could anyone point me to a book or outline the methods used to actually calculate the 532 arcseconds per century that Newtonian theory apparently predicts for Mercury's precession. I am completely ...
0
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0answers
60 views

Why does a velocity that gives gravity's centripetal acceleration make you stay in orbit?

Explanations of basic orbital mechanics that I can find all go, $$\frac{v_{satellite}^2}{r} = a_c = \frac{F_{gravity}}{M_{planet}} = \frac{(\frac{G M_a M_s}{r^2})}{M_{planet}}$$ , and so you get a ...
4
votes
2answers
99 views

If maximum speed limit $c$ is made infinite, will general theory of relativity become equivalent to Newton's gravitational theory?

We know that special relativity tends to become equivalent to classical theory of relativity as the speed limit of nature becomes infinite. If this happens, clock will tick at the same rate ...
-3
votes
4answers
111 views

Orbits for dummies [duplicate]

In a certain universe a perfectly spherical, uniformly dense planet is found to be in a stable orbit around a stable star. The rest of the universe is empty space with no silly stuff like dark matter. ...
3
votes
3answers
371 views

Why the $r$ is cubed in the vector notation for of Newton's Law of Universal Gravitation? [duplicate]

I'm learning about astrodynamics on my own and I was wondering why the $r$ is cubed in the vector notation for of Newton's Law of Universal Gravitation: $$\vec{F}_g=\frac{Gm_1m_2}{|\vec{r}|^3}\vec{r}$...
0
votes
2answers
52 views

Why doesn't the gravitational force have a permittivity in its formula? [duplicate]

We know that the electrostatic force between two charges depends on the medium between the charges and its permittivity. Why, then, doesn't the gravitational force depend on the medium?
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0answers
64 views

Are tides just very very very weak spaghettification?

I was wondering as to why there are two tidal bulges instead of just one on Earth, and then I saw this diagram: The oval shape that the Earth's water is transformed into in this image reminded me of ...
1
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1answer
35 views

What is the gravitational/electric/inverse-square field inside a cylinder?

I've read from the shell theorem that an inverse-square potential has zero field inside a spherical shell. What about the field inside a cylinder? Are objects inside a long cylinder attracted to the ...
15
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4answers
4k views

If water is essentially incompressible, why are there tides?

So recently we were taught in school that tides are formed because the moon 'cancels out' some of the earth's gravity, and so the water rises because of the weaker force. But if water is not ...
5
votes
3answers
414 views

Terminal velocity after vertical launch

If an object is launched directly up at its terminal velocity, will it have enough time/energy to reach its terminal velocity again before it hits the ground, or will drag prevent this? In this case, ...
1
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2answers
72 views

Which timestep should I use for a $N$-body simulation of the Solar system?

I am trying to implement a $N$-body simulation of the Solar system and I am stuck on the issue of the simulation timestep size. At first I would like to use a simple Euler stepping scheme. Knowing ...
2
votes
2answers
90 views

Question about inertial mass and gravitational mass

I know that inertial mass $m_i$ is the quantity that appears in Newton's second law: $F=m_ia$ and that gravitational mass $m_{g_1}$ is the quantity that appears in Newton's gravitational law: $F_g=Gm_{...
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1answer
41 views

Unification of Newtonian gravity and electrostatic force [closed]

Can we not unify Newtonian gravity & electrostatic force? All properties are almost same. We can imagine the atoms of the Earth's core to become dipoles when a body is freely-falling. Thus, due to ...
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2answers
50 views

Problem with derivation of potential enery of two body in Gravitational energy

Maybe what I'm going to ask sounds stupid but it means a lot to me that's why I'm asking. I've problem with just a single step in derivation. Let's start. I'm keeping in mind the direction of each ...
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2answers
43 views

Reference frame, gravitation and kinetic energy

English is not my primary language. I apologize (and would like corrections) if the terms I use are not the right ones. In a geocentric reference frame, the moon rotates around the Earth. So its ...
46
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4answers
3k views

Why do some location on Earth have only one tidal maximum per day instead of two?

Most places in the ocean have two high tides and two low tides per "day" (~25 hours). But I remember reading that some locations only have one of each per day. This answer has some great explanations ...
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2answers
73 views

Proportional acceleration due to changing density of the Earth

My question has to to do with a recent video Minutephysics posted about the time it takes for a person to fall through the earth, found here http://www.youtube.com/watch?v=urQCmMiHKQk At around 4:05,...
1
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1answer
91 views

Period of a pendulum [closed]

In the book 'Calculus the Early Transcendetals' at page 776 (7th edition) they give that the period of a pendulum with length $\text{L}$ that makes a maximum angle $\theta_0$ with the vertical is: $$\...
0
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1answer
87 views

As planets orbit around the Sun, does the force of gravity due to the Sun remain constant?

I know that the force of gravity is: $$F = GMm/R^2$$ Where $G$ is gravitational constant, $M$ is mass of sun, $m$ is mass of the orbiting planet and $R$ is the distance between the center of their ...
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0answers
61 views

Does a ball bearing cause bigger tides than the moon?

As per the answer to this question it is suggested the relative tidal pull of objects of equal angular area is equal to their relative density. Which lead me to the click-baity question: Does a ball ...
0
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2answers
52 views

Would an astronaut floating in space at zero speed get drawn to the Earth?

The question came to mind after watching this video: http://www.youtube.com/watch?v=MTY1Kje0yLg If the Earth and Moon can bend space-time, and if the Earth's gravity is strong enough to reach the ...
4
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1answer
98 views

Why didn't I beat the avalanche?

Yesterday, while skiing out of bounds on the south west canyons of Mt. Hood, I experienced a small and extremely mild quake. This, combined with the melting conditions caused an extremely small ...
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2answers
51 views

Calculate gravity between two points

I am trying to build a simulation of gravity in LibGDX using Bullet physics. To simplify it, I just want to apply a force on some body towered a (0,0,0) point. I got my body mass and it's location ...
3
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1answer
36 views

Orbital parameters of more than two bodies

I am not even entirely sure that the question makes sense except in certain simple cases, but let me explain what I am trying to do, but with the question first. The question is essentially: Given n ...
0
votes
1answer
64 views

Gravity Sun Earth Moon [duplicate]

The gravitational pull the Sun has on the Moon is roughly two times greater than the pull the Earth has on the Moon. If this is the case, why does the Sun's gravity not pull the Moon away from the ...
1
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0answers
39 views

Centre of gravity of system [closed]

We have a uniform rectangular tray of dimensions 40x60, with weight 3. We place the coordinate axes in such a way that the bottom-left corner of tray is at the origin and the tray sides are parallel ...
5
votes
1answer
97 views

Trying to understand Newtonian limit of GR

First ever post - please be kind. I'm trying to understand how General Relativity becomes equivalent to Newton's laws of motion, plus Newton's law of gravitational attraction in the limiting case of ...
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0answers
26 views

falling in a gravitional field [duplicate]

It is often stated that masses fall at the same rate towards the Earth at the same rate (barring things like friction), and this seems to be quoted as the Equivalence Principle. Is this statement ...
0
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1answer
42 views

Velocity Related To Gravitation [closed]

Which Equation is correct $v^2=\large{\frac{2GM}r}$ OR $v^2=\large{\frac{GM}r}$? I am getting confused here.
0
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2answers
47 views

Why did Trebuchet have so long throwing arms?

Have a look at such an historical Trebuchet: As you can see, the throwing arm (left) is much longer than the weight arm (right). Law of conservation of energy says, potential energy from the ...
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votes
2answers
78 views

Use equations to create a realistic problem [closed]

Given the following equations: $100$ m = $0$ m + ($50 \cos\theta$ m/s)$t_1$ $0$ m = $0$ m + ($50 \sin\theta$ m/s)$t_1$ - $\frac{1}{2}(9.80$ m/s2$) t_1^2$ I am supposed to make up/create a real-life ...
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0answers
17 views

About the use of Newtonian Relations for the movement of stars in the Galaxy [duplicate]

From a General Relativity point of view Gravity is given as the result of spacetime curvature interacting with energy-mass density. To get to the Newtonian limit one needs to take a) Non-...
0
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0answers
18 views

How is the centrifugal force responsible for Earth's oblateness? [duplicate]

I'm having serious problems understanding the centrifugal force caused by Earth's rotation. How does it affect the Earth's shape? Should I draw the gravitational acceleration (the one in Newton's ...
0
votes
3answers
84 views

Gravitational acceleration of asteroids [closed]

If an asteroid is moving through space at a speed that exceeds escape velocity of the earth and that asteroid is on a collision course with the earth will the asteroid Accelerate as it falls into the ...
0
votes
3answers
41 views

Finding an object's final velocity with distance dependant force [duplicate]

I am (just for fun) trying to calculate the velocity with which the moon would impact the earth if it stopped orbiting and simply headed towards earth. I know the force is $\frac{G m_1 m_2}{r^2}$. ...
-3
votes
1answer
75 views

Need motion equations for falling ball for simulating [closed]

I am currently M.S student in artificial intelligence(A.I) and working on my thesis on reinforcement learning, which robot should learn by itself how to control a quadcopter. Long story short, I have ...
0
votes
4answers
124 views

Why the pressure in liquids only depends on the height?

look at this picture : and also look at this one: imagine that the surface area of both is the same and both of them are full of water. My question is that why they both are pressing the beneath ...
3
votes
1answer
74 views

Will centre of gravity coincide with centre of mass if density of object is non uniform?

I read that for bodies of very large dimensions, but having non-uniform density, the centre of gravity does not coincide with centre of mass. I can understand that with large dimensions the strength ...
16
votes
8answers
4k views

Why doesn't orbital body keep going faster and faster? [duplicate]

If we consider the change in velocity during an infinitesimal interval of an orbit: where body B is orbiting body A, we can see that the magnitude of the resultant vector (the green arrow) is ...
6
votes
1answer
279 views

Why is the gravitational constant so difficult to measure?

The gravitational constant seems to be very low precision. For example, in the Wikipedia article recent measurements are given as having the significands of 6.67 and 6.69, a difference of 2 parts in ...