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

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Why does matter gather as discs around massive objects? [duplicate]

Why do discs, like rings of Saturn and the spiral shape of our galaxy form around massive objects, instead of just a (spherical?) cloud of matter?
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2answers
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Why is $\pi$ used when calculating the value of $g$ in pendulum motion?

I am trying to intuitively understand why $\pi$ is used when calculating the value of $g$ using the harmonic motion of a pendulum: $$g ~=~\frac{4\pi^2L}{T^2}.$$ Does it have something to do with the ...
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1answer
88 views

What is $g$ when traveling quickly around a planet?

I am trying to model a rocket orbiting a planet. I want to simplify the problem so that the rocket is travelling along an infinitely long flat surface with a $g$ along the $y$-axis. This is what ...
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1answer
40 views

Catapult projectile with different mass [closed]

We have a physics law. We made catapult and we have to launch a water balloon. However before that we have to know where the water balloon will fall. We don't have radars or stuff like that to ...
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3answers
628 views

While finding escape velocity, does human mass counts as the mass of Earth?

Escape velocity depends upon the mass of earth. my doubt is whether human mass adds into it or not? If it add then Earth's escape velocity would be increasing!
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6answers
1k views

Why does the moon stay with the Earth?

Naturally, I know it to be true that the moon goes around the Earth and that the Earth goes around the sun. However, attempting to picture this has confused me a bit. Why doesn't the moon just get ...
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3answers
84 views

Why is Earth's gravity stronger at the poles?

Lots of places state that the Earth's gravity is stronger at the poles than the equator for two reasons: The centrifugal force cancels out the gravity minimally, more so at the equator than at the ...
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1answer
55 views

How would the solar system change if the Earth were removed

I was reading a closed question with the same title and wondered if it would be on-topic with the following change: Could a large-mass object from interstellar space pass through the inner ...
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6answers
277 views

Why is kinetic energy stored as potential energy in a body during its motion against gravity?

Everyone knows kinetic energy is converted to potential energy in the body when it moves up against the earth's opposing gravitational force. But I am facing some problem with this. What I learnt ...
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75 views

Space Elevator: how would you keep the end of a Space Elevator's cable rigid?

I had a discussion with my wife about physics behind a Space Elevator. Imagine a cable rising 60k into the firmament for its elevator to climb. The cable would have to rotate in unison with the earth, ...
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1answer
21 views

Correcting for oblateness of the Earth [duplicate]

I'm trying to model numerically the effects of the Earth's oblateness on satellite orbits. I'm seeing precession of the orbit, but not in the plane that I'm expecting. Here's my corrected grav. ...
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3answers
176 views

Two bodies of finite size treated as two point masses in Newtonian gravity

When discussing gravitation between two bodies of finite size, for instance Earth around the Sun, we suppose the mass of Earth and the Sun to be perfectly localized at the center of each body. Is this ...
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1answer
70 views

Why is $d$ generally not used instead of $r$ in Newton's derivation of force of gravitation? [closed]

In Newton's law of gravitation we take distance between two bodies $r$ and represent it in the form of $r^2$? Why don't we take distance as $d$?
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1answer
83 views

Modifying Newtonian gravity to fit observed precession of Mercury's orbit

The idea is to modify Newtonian gravity so that it fits measurements of orbits around the sun. For example the precession of Mercury's orbit unlike Newtonian $n$-body simulations. I'm currently not ...
4
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1answer
75 views

How big can a cube-shaped planet be? [duplicate]

There can be small cube planets or asteroids, but as they get bigger, the gravitational force compresses them to a sphere. But what is the maximum size?
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2answers
48 views

Does the gravitational acceleration change value with height?

My prof asked me to do a graphic of a given function and I have to just to vary the gravitational acceleration $g$ and the height $H$. If I know the interval in which $H$ is defined :$[500,2000]m$, ...
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0answers
61 views

How to show circular orbit as a precessing ellipse

A uniform distribution of dust in the solar system adds to the gravitational attraction of the sun on the planet an additional force linear in $r$ where m is the mass of the planet, k is a constant ...
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2answers
82 views

How did Isaac Newton figure out how the law of gravity worked? [duplicate]

There are this and this similar Phys.SE questions, but I didn't find what I'm looking for, nor was the person's question specific enough. How did Newton figure out $$F=GMm/ r^2~?$$ What was his ...
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Two bodies of equal mass thrown from a height-Practical physics question

I have a doubt about this question: Two bodies of masses $M$ and $m$ are allowed to fall from the same height. If the air resistance be the same for each of the bodies, will the two bodies reach ...
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1answer
77 views

How did Newton discover the universal law of gravitation?

I am having trouble comprehending how anyone could come up with this formula: $F = \frac{GMm}{d^2}$ Could someone walk me through this?
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1answer
64 views

Integrals and Legendre Polynomials

I was told by a professor that this equality: $$\frac{1}{2\pi}\int_0^{2\pi}\frac{1}{|r-r(\varphi)|}d\varphi = \frac{1}{r}\sum_0^{\infty} \bigl(\frac{a}{r}\bigr)^n{|P_n(0)|}^2$$ ( where: $a$ is the ...
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2answers
120 views

Weight versus gravitational force [duplicate]

What is the difference between weight and gravitational force? I am a beginner who want to study physics properly.
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80 views

If mass is added to a toy car does it affect its speed making it faster

If mass is added to a toy car (29.7g) and dropped down a wooden ramp would it affect its speed making it go faster? I know friction comes in to play to, so if you could give me an answer or an ...
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3answers
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Acceleration of an object dropped inside an accelerating elevator

A stone is released from an elevator going up with acceleration of $g/2$. What is the acceleration of the stone just after the release? The answer is $g$. Shouldn't the stone carry the acceleration ...
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1answer
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Martian space elevator from the vulcano Olympus Mon to the moon Phobos?

In my fascinating imagination, I am seeing a space elevator from the vulcano Olympus Mon to the moon Phobos. Phobos also seems to keep spaceships - while a smaller shuttle attaches itself to the ...
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2answers
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Gravitational field strength inside the Earth [duplicate]

please could someone give me a relatively straight forward answer why the gravitational field strength follows a straight line (linear) relationship with distance from the center of the Earth but when ...
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31 views

Could an object higher than the stationary orbit be returned to the outgoing point on this orbit?

In the question Centrifuge speed of an object higher than a stationary orbit, I asked: Does an object higher than the stationary orbit move slower or faster around the world than the top of a tower ...
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Centrifuge speed of an object higher than a stationary orbit

In the question At what altitude above equator do gravitational and centrifugal forces cancel each other?, I asked how high a tower on the equator has to be such that at its top, gravitational and ...
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2answers
80 views

At what altitude above equator do gravitational and centrifugal forces cancel each other? [closed]

How high has to be a tower at equator to get on its peak the same - but of course inverted sing - value of gravitational and centrifugal forces?
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1answer
103 views

Why is the gravitational field potential scalar?

On page 48 of Carroll's Spacetime and Geometry he, before introducing "gravity as geometry", discusses the classical Newtonian equation: $F_{g}=-m_{g} \nabla \Phi$ This equation is very straight ...
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109 views

Why $r^2$ and not other power of $r$ in mutual force of gravitation?

My book introduces force of gravitation as a non-contact force between two bodies of mass $M_1$ & $M_2$ seperated by $r$ . Then it says it is directly proportional to the product of masses ...
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0answers
61 views

Potential due to a Uniform Ring [closed]

Consider a uniform ring of mass $M$ and radius $a$ (?). I would like to prove that for $r > a$: $$\Phi(r) = \frac{GM}{r} \sum_0^\infty[P_n(0)]^2 \left(\frac{a}{r}\right)^n $$ Where $\Phi(r)$ is ...
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What is “W external” and “W internal” in Energy conservation law?

When I solve the energy conservation problem, I am confused when I have to make the term positive or negative. For example, someone throws a ball right up to the ground with velocity, $v$. The ball ...
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1answer
77 views

Does Newton's first law apply also to non-newtonian physics?

I think I understand than an example of Newton's first law (intertial frames) would be a single asteroid in vaccum with no other bodies around, a comet in such free space or likewise. Then I think the ...
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1answer
50 views

An alternate approach to find variation of gravitational acceleration with respect to depth of an object in Earth

As we go down the Earth, assuming it to be a uniform sphere abiding only to Newtonian physics, the gravitational acceleration imparted to an object by the Earth goes on decreasing, and decreases to 0 ...
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6answers
242 views

Trouble understanding the concept of true and apparent weight

I need help understanding the concept of true weight vs apparent weight. I understand this much: if someone is standing in an elevator on a scale, the further up they go the less the reading on the ...
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2answers
64 views

Time for launched object to reach point in space

I am attempting to calculate the time required for an object launched perpendicular to the surface of the earth at escape velocity to reach an arbitrary point in space (neglecting rotational velocity, ...
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0answers
10 views

Is it possible to calculate Lagrangian isolines for local stars?

Is it possible to calculate Lagrangian isolines for local stars? SciFi descriptions of 'hyperspace' always talk about travel routes between the stars following some sort of route. As a thought ...
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1answer
36 views

Calculating $g$-force in between planets

The g-force is given by $1 + \frac{a}{g}$. The question is that a rocket is accelerating from between Mars AND Juptier at 26.95m/s. The astronaut in focus is 60kg (irrelevant I believe). Using this, ...
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1answer
116 views

Is relativistic event horizon half of Newtonian event horizon?

Is Relativistic event horizon half of Newtonian event horizon? relativistic escape velocity formula (from $m\phi=E-E_0$) is $v_e=\sqrt{2\phi-(\frac{\phi}{c})^2}$ and the Newtonian version of the ...
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3answers
118 views

How fast would the Earth need to spin for us to feel weightless?

It's a classic question with many answers all over the Internet, but none here so I figured I'd ask it: How fast would the Earth need to spin for a person (or anything for that matter) to feel ...
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2answers
163 views

Energy to reach the moon

I've been stuck on this question for a couple of days now. Given that the potential energy of a 930 kg object on the Earth's surface is -58.7GJ, calculate the minimum energy required for the 930 ...
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3answers
181 views

Armageddon prevention

I was watching the movie Armageddon and it made me think of a few things. We would probably not need to send a crew to blow the asteroid in two, I think we could still send a warhead with enough power ...
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1answer
29 views

Gravitiation force of a sphere

Was wondering about Shell Theorem, specifically about the immediate results. Force (on a point mass) inside a shell is 0. Force (on a point mass) outside a shell is GmM/r^2 From what i know the ...
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1answer
45 views

What is the simplest way to perform a Cavendish experiment?

The Cavendish experiment is cool, but seems complicated to experimentally perform. What is a simple way to recreate the experiment?
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10 views

Having trouble reconciling Newtonian-derived earth mass with direct calculation [closed]

Our calculation of Earth's mass as $M_E=5.97\times 10^{24} \:\mathrm{kg}$ is made by observing the gravitational interaction between the moon and the earth and then solving the relation ...
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1answer
35 views

General potential of rotating system

I'm new here at the physics site, and not really that deep into the area of which i'm going to ask a question about now. Therefore please feel free to ask clarifying questions. I'm trying to deal ...
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2answers
96 views

Why are some forces not included in the sum of forces?

I was given the following notes in class: 4.32 A skier of mass $65.0\text{ kg}$ is pulled up a snow-covered slope at constant speed by a tow rope that is parallel to the ground. The ground ...
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19 views

Reason behind the rotation of Earth? [duplicate]

I want to know what is the reason that the Earth rotates on its own axis? What are the forces responsible for the Earth's rotation?
2
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1answer
77 views

Velocity of satellites greater than required velocity

We often find velocity required to keep a satellite in orbit by the formula $v=\sqrt{\frac{GM}{r}}$ where $v$ is perpendicular to the gravitational force. It is very intuitive that the object will go ...