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

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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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2answers
1k 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
187 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
1k 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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3answers
13k 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
2k views

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
146 views

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
603 views

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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2answers
78 views

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
132 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
847 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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2answers
239 views

Why $1/r^2$ and not another power of $r$ in Newton's law of gravitation?

My book introduces the force of gravitation as a non-contact force between two bodies of mass $M_1$ and $M_2$ separated by a distance $r$ . Then it says it is directly proportional to the product of ...
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2answers
311 views

7 Billion people jumping at once

What would happen if every person in the world gathered at a minimum possible area and jumped all at once? Would that have any effect on Earth?
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0answers
53 views

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
383 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
134 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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7answers
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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
121 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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1answer
79 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
300 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
2k 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
501 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
322 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
58 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
495 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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1answer
77 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
201 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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1answer
124 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 ...
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1answer
185 views

Giant leap of the space goat

This problem was inspired by this Math.SE post and similar problems involving tethered animals. A space goat is tethered to the north pole of a spherical asteroid of uniform density and radius $a$ ...
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2answers
6k views

Work done against gravity [closed]

The work done against gravity is $mgh$, well at least that's what my textbook says. I have a question: I can apply a force say 50N, so total work done = $mgh + mah$. Where $ma$ = Force. But the truth ...
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1answer
147 views

Earth-Moon system

While learning about motion of centre of mass, I came across this statement online, It is also more accurate to say that the Earth and Moon together revolve about their common center of mass. ...
3
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3answers
994 views

Escape velocity of satellites

I know that the equation for it is $$v^2 = \frac{2GM}{r},$$ and with that, the rocket should be launched at that speed. But could it go much slower spending much more fuel to escape from gravity right?...
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0answers
29 views

Does gravity weaken by the square of the distance because the energy is dispersed over the square of the distance [duplicate]

The area of a circle is $\pi r^2$ if you increase $r$ the area will increase by the square so if this area was of energy and you increase the area it is dispersed you would expect its energy to weaken ...
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5answers
7k views

Is this scene from the A Team explainable by Physics?

This scene (youtube link) from the movie The A-team, the four members are in the tank and its falling from the air, they fire the canon and it slows the tank from falling for a moment before falling ...
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1answer
838 views

How can a planet gravitationally capture objects?

I would expect that any asteroid or other object originating far away but passing near a planet would pick up speed and energy as it approaches, but unless it comes into contact with the atmosphere (...
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2answers
3k views

Projectiles Launched at an Angle with unspecified Initial Velocity [closed]

I'm attempting to do my Physics homework, and I did the first one right, but that problem gave me initial velocity. This problem gives me only the angle relative to horizontal and the distance it ...
3
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2answers
82 views

How to calculate gravitational force

Suppose the centre of mass of 2 bodies coincide , then how will we calculate the gravitational force between the 2 bodies ??
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2answers
184 views

Find net force on a mass centered between four other masses

I'm not going to post the full question, I just want a general idea of how I should go about solving this type of problem. There is a square with 4 charged masses on each of the corners, in the ...
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1answer
212 views

From Paris to … London [closed]

(Excuse the pun in the title, couldn't resist) Paris and London are connected by a straight underground tunnel, as shown in the diagram below. A train travels between the two cities powered only by ...
69
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4answers
8k views

Where does the extra kinetic energy come from in a gravitational slingshot?

I read in this answer in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the ...
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3answers
148 views

Question on acceleration of gravity

In pre-calculus last week my teacher explained a scenario in which a man throws a rock down a well and takes 4 seconds for you to hear the rock hit the bottom. How far downs the well? Last years I ...
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0answers
48 views

Do we weigh less in the morning? [duplicate]

A question on Biology SE got me thinking, ignoring weight naturally lost during the night, "Do we weigh less in the morning?" During the night, the sun is above us, and the earth below us. Conversely,...
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5answers
7k views

Why are orbits elliptical? [duplicate]

Just wanted to know why planetary orbits get to be elliptical? I'm not debating how stable these orbits are (obviously almost completely stable), but why don't planets revolve in the special ellipse ...
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1answer
116 views

Why is gravitational potential energy negative? [duplicate]

Why is gravitational potential energy negative? How is it different from other forms of energy? I recently saw a video by Dr. Michio Kaku, he said that the total energy content of the universe is zero,...
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3answers
535 views

Advantages/Disadvantages of “hanging off” a motorcycle when leaning

The closest question I could find with regards to this subject was this one: Countersteering a motorcycle However, it does not address the specific physics of what I would like to know. There are 3 ...
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5answers
691 views

Satellite Collision Problem

I'm stuck on a problem of two satellites going towards each other. The mass of the first satellite is 400kg and the mass of the second satellite is 100kg. The altitude of the satellites is 1000km. I ...
9
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2answers
1k views

How does escape velocity relate to energy and speed?

I have several confusions regarding escape velocity. I am sure I am missing something(s) obvious or maybe I am taught wrong. Lets say we throw an object of any mass at exactly escape velocity of ...
2
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1answer
131 views

Weight held by jet stream of water

Consider a bucket of weight $W$, held in air by a jet stream of water from the ground (moving vertically upwards) at height $h$. The water is fired from the ground at the rate of $\mu$ (units kg/s) ...
2
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2answers
726 views

Why doesn't gravity bend everything equally?

If gravity is the curvature of spacetime it should bend everything equally. To clarify my point I would like you to imagine two scenarios. Think of a bird flying in the storm while the wind is blowing ...
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3answers
418 views

Work done by gravity on a ball & the ball on earth

I have studied today that if a ball was to fall a certain height, then the work done by gravity on the ball would equal the work done by the ball's equal and opposite gravitational pull. By $W=Fd$, ...