# Tagged Questions

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

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### Gravitational Null Point between Earth and Moon

I need help finding the gravitational null point point between the Earth and the Moon, the point beyond which you start falling towards Moon. I am having difficulty in taking into account the orbiting ...
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### Why is Larry Niven's Ringworld Unstable?

In his 1970 science fiction novel Ringworld, author Larry Niven describes the eponymous Ringworld, a gigantic structure shaped as a ring with a radius of around 1 AU, rotating around a star in 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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### Derivation of Kepler's laws

How can analytically be derived the Kepler's laws? I found some extremely synthetic equations which from the Newton's laws (in particular $\mathbf{F} = m \mathbf{a}$) tried to obtain the Kepler's ...
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### Solving the Three-body problem numerically

I want to create a program in $Mathematica$ that solves numerically the Three-body problem by Euler-Lagrange's equations. I was searching some methods to sucessfully do it. So I found a way to solve ...
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### On the Stability of Circular Orbits

Bertrand's Theorem characterizes the force laws that govern stable circular orbits. It states that the only force laws permissible are the Hooke's Potential and Inverse Square Law. The proof of the ...
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### Would you be weightless at the center of the Earth?

If you could travel to the center of the Earth (or any planet), would you be weightless there?
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### Gravity on other planets [closed]

Why we use the word"Earth' pull" while defining gravity when gravity also exist on other planets of solar system?
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### Question on motion of vehicles [closed]

What are the forces or moments reduces speed of an object while climbing?
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### How far would an arrow go in a space station and still be deadly?

So I was answering a question on the WorldBuilding SE site and one aspect of my answer made me wonder. Imagine you are on a massive space station of unlimited size. If you were to fire an arrow from ...
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### Why does weight on Earth have a tangential component?

I read in Pulsar's answer of this question that weight has a tangential component due to the rotation of the (assumed spherical) Earth but I don't understand this. Can someone expand on it please?
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### Understanding the math behind a falling object attached to a parachute

I'm trying to understand the mathematics behind calculating the total speed and force of a $40 kg_f$ object hooked up to a parachute, falling to Earth. From what I understand, the formula for this is ...
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### As The World Turns 2

When dinosaurs roamed the Earth was the Earth rotating faster creating less gravity to allow for their size? How much would 100 kg weigh then?
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### How the apparent weight varies due to the rotational motion of Earth?

I learned that as the earth rotates about its axis, the bodies on the earth also follow a circular path. In most books I read, they give the example of a person standing on a weight balance at the ...
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### Weight Detection Under Concrete/Asphalt [closed]

Consider that a weight sensor was embedded in a road. Would cars that drive over it trigger the sensor? I was thinking it'd look something like this (if we ignored the downward force that the ...
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### Why is the Moon considered the major cause of tides, even though it is weaker than the Sun?

You have likely read in books that tides are mainly caused by the Moon. When the Moon is high in the sky, it pulls the water on the Earth upward and a high-tide happens. There is some similar effect ...
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### Newton's 1st law [closed]

If all of a sudden the gravitational force and gravity disappears then the planets would still continue to rotate and revolve ? Give reason
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### $1/r^2$ gravitational force of triangles in 2D

Suppose I have two triangles relatively close together (so they probably shouldn't really be treated as point masses). I want to calculate the gravitational force (and potentially torque?) generated ...
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### Dynamics of pairwise distances in the $n$-body problem

Consider the $n$-body problem where we are interested in describing the time evolution of $n$ masses interacting through a potential $U$. Let $D$ be the matrix containing all pairwise distances ...
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### How does gravity work underground?

Would the effect of gravity on me change if I were to dig a very deep hole and stand in it? If so, how would it change? Am I more likely to be pulled downwards, or pulled towards the edges of the hole?...
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### How deep does a gravity well need to be to remove particles from a planetary body?

I almost considered asking this question on WorldBuilding, however I wanted the brute mathematics on the subject, so please excuse the theoretical nature of this question. I understand the basic ...
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### How would you go about solving this graphical mass problem? [closed]

I've tried finding the x and y components of the vectors created by each mass to find the resulting vector's magnitude. However, my answer of 0.354 N keeps getting marked wrong. Any ideas on how to ...
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### Potential Energy = mgh. What is the name of this principle and did Newton discover it?

Somebody I know keeps trying to convince me that Potential Energy $PE=mgh$ is one of Newton's Laws (as well as the closely related idea, Work Done = force x distance moved). I am fairly certain that ...
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### What is the significance of the Inverse-square law? [duplicate]

Considering its occurrences in various fields like Electrostatics, Gravitation, Acoustics etc. how does the law bind these topics together?
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### Free fall vs throw with air resistance

If I let a stone drop from a certain height and throw a stone from a certain height, with air resistance, which will reach the ground first? When I draw a free body diagram the air resistance in the ...
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### If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, ...
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### Gravitational force when standing on an infinite disc

If a person were to stand on a flat disc of thickness 1 meter but infinite diameter, would they experience finite or infinite downward force? There is an infinite amount of mass, all of which ...
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### Acceleration as a function of time in Newtonian gravity [duplicate]

In Newtonian gravity, you have acceleration as a function of separation distance $r$ as $a(r) = GM/r^2$. I need to derive acceleration as function of time, i.e. $a(t)$. PS I got into this when I ...
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### What's my $\mathrm dM$? Gravitational Potential inside a circle of mass

I'm trying to find the gravitational potential for an arbitrary point within a ring of uniform mass density. The point is constrained to be in the same plane as the ring. So we start with: \Phi=\...
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### Weight Distribution of granular piles

I was recently at a farm watching piles of grain being formed in the shape of enormous cones. Each of these grain stacks weighs in excess of 50 tonnes. I am not a physicist but I am very curious as to ...
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### Gravity - What happens when two objects of unequal masses fall freely towards the ground? (Revisited)

The common perception regarding what happens when two objects of equal sizes but unequal mass are allowed to fall freely towards the ground is that - both the objects make contact with the ground at ...
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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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### How can I measure the stability of a many body gravitational system?

Suppose I have an N body planetary system interacting via gravity. Suppose I know the positions and momenta at t=0. How do I know if this system is stable (indefinitely)? By stable I mean the ...
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### Relation between gravitational field and gravitational potential

The gravitational field is the negative differential of the gravitational potential. Now the gravitational potential due to a particle at a distance $r$ is $-Gm/r$ where $m$ is the mass of the ...
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### Tidal effect on planet with two moons

If an Earthlike planet had two moons, one relatively smaller and closer while the other was bigger and farther away, and one had a prograde orbit while the other had a retrograde orbit, in what ways ...
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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 ...