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

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Work done by a homogeneous gravitational field on a system of particles

Perhaps this is trivial: how does one prove that the work done by a homogeneous gravitational field on a system of particles is equal to the work done on a point mass with the total mass of the ...
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2answers
152 views

Why do things here on Earth fall down? [closed]

I want to have an answer with that question above for my physics lesson. I really don't have an idea about it, so, I ask help from you guys and hope that someone can help me with it.
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1answer
68 views

What is the ultimate “goal” of two particles in a gravitational field? [closed]

What is the ultimate "goal" of two particles in a gravitational field? Will the particles eventually occupy the same point at the same time if nothing stops them? What stops them from achieving the ...
2
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0answers
102 views

If the field concept was invented by Faraday, then how did Newton interpret the $g$?

This is Newton's law of universal gravitation. $F=G\frac{m_1.m_2}{r^2}$ Gravitational field $g$ is derived from this formula $g=G\frac{m_1}{r^2}$ This is named gravitational "field" strength. If ...
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1answer
124 views

Gravitation between a homogeneous ring and a mass [closed]

I got a problem with describing the gravitational attraction between a homogeneous ring and a point mass. Let $m$ be the point mass as showed in the picture, lying a $x$-distance away on the ...
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0answers
95 views

Will relativistic glider cause lower gravitational force in Newtonian gravitation?

In the articles The relativistic glider and The relativistic glider revisited, the relativistic glider is proposed where a quasi-rigid body can slow down its fall under gravity without any reaction ...
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2answers
593 views

Potential energy $= mgh$, what is $h$?

NOTE: when I say potential energy I mean gravitational PE The formula for potential energy is P.E = mgh. What is h referring to? Height, obviously. Consider the example: What is the potential ...
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2answers
2k views

Which ball falls faster, the cool one or the hot one?

Suppose we're on the top of the Tower of Pisa (or a larger version of it) with two identical cannonballs. We heat one up (say, to 200 degrees Celsius, or some other high temperature before it starts ...
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2answers
179 views

Heating of two identical balls [closed]

You are given two identical steel balls of radius (say) 5 cm. One ball is resting on a table, the other ball is hanging from a string. Both balls are heated (with a blow torch) until their radii have ...
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2answers
138 views

If earth stopped spinning how much heavier would 1kg feel [closed]

My girlfriend seems to think if the earth stops spinning we will all fall off However, she did spark my imagination, due to centripetal force things must feel lighter then they otherwise would on an ...
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3answers
575 views

What is gravity and what causes objects to act against it?

So I understand the concept of gravity, in that it's not actually a force, but more of a displacement in the spacetime grid. An object with a big enough mass will bend the spacetime, causing smaller ...
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3answers
91 views

About Kepler's Law

When Earth goes near the Sun, its velocity increases and when it goes far from the Sun its velocity decreases. Then why according to Kepler's law is the time period $T^2 \propto a^3$, where $a$ is the ...
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1answer
227 views

Work performed by a stationary object in a gravitational field “on Earth”

I was thinking about this problem: How much work is required to hold an object stationary in a gravitational field? or: How much energy is required to keep an object stationary in a ...
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3answers
101 views

Does uniform distribution of background matter affect the dynamics of a gravitational system?

Situation 1: A test particle of mass m moves around a big mass M in a Keplerian orbit. The orbital period is easily found, given certain initial conditions. Situation 2: The same system of two bodies ...
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0answers
74 views

What did Feynman mean by “gravity itself is a pseudo force”? [duplicate]

Feynman writes: One very important feature of pseudo forces is that they are always proportional to the masses; the same is true of gravity. The possibility exists, therefore that gravity itself ...
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2answers
74 views

Can gravitational constant be changed?

In my book(Principles of Physics by Resnick,Halliday,Walker) , the authors write: If $G$ - by some miracle - were suddenly increased by a factor of 10, you would be crushed to the floor by Earth's ...
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3answers
255 views

When we catch a falling object, where does its kinetic energy go? [duplicate]

Some of it is transformed into heat and noise, but where does the rest go? Further details: The object does not bounce off (e.g. a sack of rice marble ball). The hand remains completely static ...
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10answers
3k views

In reverse time, do objects at rest fall upwards?

I want to develop a game where time runs backwards, based on the idea that physical laws are reversible in time. However, when I have objects at rest on the earth, having gravity run backwards would ...
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1answer
86 views

How does one reduce the apparent effect of gravity without falling? [closed]

There are things like the Vomit Comet to simulate zero-gravity for small periods, but that involves going into a steep dive in an airplane. How could one get the same effect on a surface of the ...
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1answer
102 views

Gravity on and inside a planet-sized bi-lobed body

Admittedly, for yet another science-fiction project Say I have a planet-like body shaped like a sphere with a torus subtracted out of it, leaving a sort of "apple core" shape. Firstly, is the ...
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0answers
27 views

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth? [duplicate]

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth? According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 ...
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2answers
134 views

Why is the potential energy for a body raised up by a height negative?

I tried deriving the potential energy of a body when raised at a height $h$ above the earths surface, using the formula: $$PE = -W_\text{conservative}$$ where $W_\text{conservative}$ is the work ...
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3answers
500 views

How to calculate the value of gravitational acceleration of my town

We normally consider the value of gravitational acceleration $g = 9.8 m/s^2$ while solving the problem. But that is the value of $g$ at poles (if I am not wrong). My teacher have given as homework ...
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2answers
842 views

How can gravity truly be infinite?

From my knowledge, gravity is infinite and extends throughout all of space. It diminishes as distance increases but is still present everywhere. So given enough time, no matter where something is in ...
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0answers
169 views

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth?

According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 Explosive Space Modulator will require $1.711 \cdot 10^{32}~\text{J}$ to shatter the Earth into a gravitationally ...
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2answers
71 views

Will terminal velocity exist on this imaginary planet?

If the atmosphere of an imaginary planet is really thin like 100 particles per cubic centimeter (density of the closest resemblance of vacuum made on Earth) and has mass say, 15 times than that of ...
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2answers
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Will a bullet dropped and a bullet fired from a gun horizontally REALLY hit the ground at the same time when air drag is taken into account?

In a world without air, I understand they definitely would. However, with drag taken into account, I think they wouldn't. Since the drag force varies proportional to the square of speed (ignoring the ...
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2answers
204 views

How much pressure does the earth's central atom experience?

If mass is distributed evenly about it: "central atom", then it should be weightless right? If reasonably so, does it still experience the pressure? I would like to calculate, but I'm not so ...
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2answers
51 views

Does juggling faster less work then juggling slower?

I got this idea when juggling. Let's say three balls with the standard technique. When I throw the balls higher it is harder (more work), but since it takes more time for them to fall back I work less ...
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2answers
130 views

My total potential energy?

The potential energy in a uniformed gravitational field is $mg \cdot \Delta h$. This assumes of course that $g$ doesn't change and only gives the difference in potential energy for $\Delta h$. How ...
2
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4answers
178 views

What is the intuition behind “Net Work is Zero”?

I tried searching the answer to this all over the internet, but still cannot grasp this concept. So, when a book is being lifted, let's say $25 meters$ with a mass of $4kg$, with constant speed. I ...
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2answers
325 views

Can very large objects have a gravitational moment?

I was reading this answer about center of gravity vs. center of mass and it stated: Consider the Sears Tower. Its CG is about 1 millimeter below its CM. The reason why is because the base of the ...
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1answer
138 views

Why does the water rise upwards when the bottle fall down with accleretion $>>g$?

When a medium-sized bottle filled with water quarterly falls from a height with acceleration $g$, the water remains calm. But when it falls with acceleration $>>g$, the water abruptly rises up ...
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4answers
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What's the difference between centre of mass & centre of gravity for massive bodies?

My book says: For most of the small objects, both are same. But for mammoth ones, they are really different ones. And in a gravity-less environment, COG is absent; COM still exists. Ok, what's ...
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2answers
62 views

How to find gravitational acceleration given $k$ in a power function

I have a problem that has been bugging me for a week, and I can't figure it out. We know the power function: $$ y=kx^n $$ I also have a set of data: I took the natural log of both of these data ...
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2answers
203 views

Pendulum's motion

Consider a pendulum in it's balance point hanging from ceiling. It can swing in all the directions in the space. The pendulum can only swing in a sphere(the string can't bend). Now, is it possible to ...
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1answer
148 views

What Is the Physics principle behind dropping a stone into a cup of water?

I have been doing an experiment about relationship between drop height of a stone and the loss of water in the cup it lands in. I found that after dropping the same stone into a cup with the same ...
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0answers
29 views

Relation of gravitational pull with no air friction [duplicate]

I am confused between the gravitational pull and the air friction on the moon. Let me give you an example, I have learned that the greater the mass of the body the more gravitational force it ...
0
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1answer
65 views

From escape velocity to gravitational acceleration

If all you are given is the escape velocity from the surface of Earth can you back calculate to Earths 9.8 m/s^2 gravitational acceleration? In the end what I am looking for is a formula with Escape ...
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1answer
102 views

How Earth's Gravity is more powerful than its centrifugal force?

How Earth's Gravity more powerful than centrifugal force? The earth spins all the time but we are not holding onto something to avoid drifting off in space cause of the centrifugal force.
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1answer
56 views

Why would we weigh less at earth's center?

why we would weigh less at earth's center(as opposed to sea level). Looking around the net, I have seen different approaches to this problem, each with different solutions. According to Newton's ...
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0answers
16 views

A falling object's position [duplicate]

I have asked this previously, with a very useful answer but I was not able to solve my problem. I'll try to make it more simple, basically: Find the radius, $r$ of an object after a time, $t$ if ...
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2answers
768 views

Calculating the velocity of an elliptical orbit

I need an explanation as to why my solution to this problem doesn't work (please do not give me an answer or tell me exactly how to do it as this is a homework question that I need to do myself, hints ...
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1answer
45 views

How to expand this equation considering acceleration due to gravity into 3D vector space?

How can we expand this following equation into 3D vector space? I learned this equation from this answer: Don't heavier objects actually fall faster because they exert their own gravity? The ...
5
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4answers
268 views

Is there a peak gravitational force between bodies?

Suppose Object A is exerting gravitational force on Object B. Object A increases in mass, and so increases in volume, increasing the gravitational force on Object B. But, since mass occupies space the ...
5
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1answer
2k views

Gravitational field intensity inside a hollow sphere

It is quite easy to derive the gravitational field intensity at a point within a hollow sphere. However, the result is quite surprising. The field intensity at any point within a hollow sphere is ...
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3answers
285 views

Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron? Will it continue its movement? If there is a gravitational ...
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1answer
90 views

A Special Case About Projectile Motion [closed]

There is a common fact about projectile motion. Let me remind you with an example: Assume that you are aiming at a hanging banana on a tree. If there were no gravitational force, the bullet would ...
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2answers
221 views

Is $F = G\dfrac{{m_1}{m_2}}{r^2}$ really true?

My book (Concepts of Physics by H.C. Verma) writes: It has been reported (Phys. Rev. Lett. Jan 6, 1986) that the force between two masses is better represented by: $$F = \frac{G_{\infty} m_{1} ...
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5answers
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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 ...