# Tagged Questions

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

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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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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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### 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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### 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 ...
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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### 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,...
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### 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 ...
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### 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 ...
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### 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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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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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### 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 ...
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### 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.
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### 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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### 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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### 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-...
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### 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 ...
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### 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 ...
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### 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 $\frac{G m_1 m_2}{r^2}$. ...
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### 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 ...
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### 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 ...
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### 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 ...