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

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Does not the mass of those living on the Earth add on to the mass of the Earth or is it too negligible to be cared for?

Source: Earth weighs about 13,170,000,000,000,000,000,000,000 pounds (or 5,974,000,000,000,000,000,000,000 kilograms). Since Earth is too big to be placed on a scale, scientists use mathematics ...
2
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2answers
110 views

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 ...
0
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1answer
75 views

Gravity Relative to Mass?

Why is it that, in basic physics, it is taught that the acceleration of gravity is the same for objects of any mass (at a constant distance from earth)? Why then is the acceleration of gravity ...
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1answer
232 views

What is the difference between an electric field and gravitational field? [duplicate]

Since the electrostatic field and the Newtonian gravitational field share a similar form: proportional to $$ \frac{1}{r^2} $$ Is there any qualitative difference between motions under the ...
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2answers
53 views

Planks, supports, and a scale [closed]

I've got two equal dimension planks with the same homogenous mass. They're placed next to each other like this (bird's eye view): [ ][ ] They're sitting ...
-2
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1answer
100 views

Why the moon doesn't fall down to earth? [duplicate]

Why the moon doesn’t fall down to the earth? We know that the moon travels in speed perpendicular to the gravity of the earth so that it doesn’t fall down to earth. But what if we supposed that the ...
-4
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1answer
58 views

Is conversion of energy into time and space possible ? [closed]

In classic mechanics mass and energy were constant dimensions. Relativistic mechanics stated that 'energy and mass' together is conserved by using conservation of energy.But cant we say that energy is ...
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5answers
16k views

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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1answer
279 views

Centre of gravity vs centre of mass for a pyramid mounted on a cube, all sides of length $l$ [duplicate]

A uniform solid body is constructed using a square-based pyramid mounted on a cube. If each edge of the solid has length $l$ show that the centre of gravity of the body lies within the cube is, $\frac ...
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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 ...
4
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4answers
662 views

A confusion regarding an example in The Feynman Lectures

In The Feynman Lectures, In the chapter entitled Work and potential energy, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable ...
2
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2answers
129 views

Finding sphere of influence in multibody system

I would like to draw a boundary illustrating the sphere of influence of each body in a 3 body system. What is the best way to find such a boundary? My understanding is at the edge an SoI is the ...
2
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3answers
120 views

Free falling body's deceleration

Ok, a body is falling with a velocity $70\sqrt{2}\ ms^{-1}$ and its final velocity must be 0 $ms^{-1}$ after falling a further 200 $m$. What is the acceleration required to bring it to a stop after ...
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4answers
89 views

$g=GM/r^2$; $M=$mass of Earth. So in center $r=0$, so $g$ should be infinity [duplicate]

From the equation of Newtonian gravitational force, we know that $$F=\frac{Gm_1m_2}{r^2}.$$ If one of the two objects is Earth, then from $F=GMm/r^2$ and we know $g=GM/r^2$. So 'g' should be infinity, ...
2
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0answers
63 views

Trouble with geometric proof of gravitational force inside a sphere

In Newton's superb theorem: An elementary geometric proof (Argument on Page 4, accompanying diagram on Page 11), the author attempts to prove Proposition 70 in Newton's Principia (gravitational force ...
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1answer
59 views

Acceleration due to gravity: what's the derivation? [closed]

Modelling the Earth as a symmetric, spherical body (and by using the law of gravitation), we come up with the equation $$w = F_g = \frac{Gm_Em}{R_E^2}$$ How do we arrive to the equation to get the ...
7
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5answers
2k views

what is the 2D gravity potential?

In 3D, I can calculate the total force due to gravity acting on a point on the surface of the unit sphere of constant density, where I choose units so that all physical constants (as well as the ...
2
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1answer
58 views

Why does Moon always poses the same face towards Earth?

If both Earth and Moon are rotating as well as revolving around some focus, shouldn't they have drifted out of phase with each other long ago? So, why do we always see the same side always?
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1answer
83 views

Is Voyager 2 slowing down?

Voyager 2 will leave the dominating gravitational influence of the Sun for a region where other stars have comparable influence on the craft. By the time it gets that far away, how much will it have ...
6
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1answer
163 views

Why doesn't space junk form a ring around Earth?

If ice and rock form rings around a planet like Saturn, why don't rings form around Earth from all of the broken satellites and other material around Earth, or will they eventually? I would expect at ...
70
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7answers
6k views

Does juggling balls reduce the total weight of the juggler and balls?

A friend offered me a brain teaser to which the solution involves a $195$ pound man juggling two $3$-pound balls to traverse a bridge having a maximum capacity of only $200$ pounds. He explained that ...
14
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2answers
742 views

Why is there no permittivity-type constant for gravitation?

When I look at electric or magnetic fields, each of them has a constant that defines how a field affects or is affected by a medium. For example, electric fields in vacuum have a permittivity constant ...
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2answers
67 views

Rockets and distance [closed]

I am trying to create an equation which allows for me to change the aspects of the rocket so i can calculate the distance traveled vertically. My idea is for a rocket that only moves vertically; ...
7
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2answers
3k views

What would a person experience in a free-falling elevator in a shaft long enough to reach terminal velocity?

Assume we had an elevator shaft long enough for a free-falling elevator to reach terminal velocity. As I understand it, when the elevator begins to fall a person inside would experiences ...
2
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3answers
166 views

Shielding of electric and gravitational force on particles inside a spherical shell

A cavity inside a conductor is shielded from outside electric influences. But, if you put charges inside the cavity, the exterior of the conductor is not shielded from the fields by the inside ...
21
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2answers
903 views

How do spiral arms form?

Why aren't all spinning galaxies shaped as discs as my young mind would expect? I understand how the innermost parts of a galaxy spin faster than the outer parts, and that could explain why some ...
3
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3answers
832 views

How far up an object is its gravitational potential energy taken from? [closed]

This is quite a brief question but, Is the $h$ value in $mgh$ taken from an object's base, middle of top. For example, if a person was $1.5m$ in height and they were standing on a hill of height ...
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3answers
441 views

Is it possible to have things orbit around us?

Since humans are not large in mass, do we exert enough gravitational force for a small object to orbit around us? (Assuming that the only gravitational force acting on the object is from the human). ...
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3answers
276 views

Fundamental paradox with Newton's Law of Gravity?

This is my first post here, but I've been struggling with this problem in my head since I studied physics at school when I was 14 (30 years ago!). There seems to be a fundamental paradox with ...
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1answer
226 views

How is the value of Standard gravitational parameter for Earth derived?

Its been a while since I've done any physics, I'm working on some orbital programs. I'm using this formula $\mu = MG$ where $M$ is the mass of the body and $G$ is the gravitational constant. The ...
1
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1answer
73 views

Can 4 collinear planets exist?

Imagine 4 planets, A has moon a and B has moon b. A and B are binary planets. Is it possible that a and b and A + B all have same the period, so that the 4 planets are collinear?
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2answers
95 views

Gravitational force acting on two particles

According to Newton's Laws of Gravitation, $F=Gm_1 m_2/r^2$ So gravitational force F is directly proportional to $1/r^2$. Now if we consider 2 point masses in vacuum at rest at a distance 'd' ...
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3answers
131 views

Is gravity actually missing or lower in certain spots on Earth?

I have heard and read about "missing gravity" in some regions of Earth. What I seemed to gather from this info is that if I go to a certain spot and jump, I can jump higher; or I could maybe lift more ...
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3answers
280 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
70 views

Clarification of the physics involved of an orbiting body in a circular orbit

I am writing a physics simulation program to simulate a body orbiting a planet but I am a little confused about the physics involved and would like some clarification. To simulate gravity I am using ...
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0answers
29 views

Misbehaving singular isothermal sphere potential

The singular isothermal sphere (SIS) is a useful simple model often used in astrophysics. It has density profile: $$\rho(r) = \frac{\rho_0 r_0^2}{r^2}$$ This is well known to have some quirks ...
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2answers
85 views

Where to use acceleration due to gravity $g\propto\frac{1}{r^2}$

I (and we all) know that acceleration due to gravity $g\propto\frac{1}{r^2}$.Now my question is can I use this for depth.If not,why?If we can use it for depth or not struck me when I was trying to ...
4
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2answers
80 views

Dimensional analysis - When can you introduce constants that make dimensions compatible?

I have just read this question: What justifies dimensional analysis. One statement was: Maybe the speed of a comet is given by its period multiplied by its mass. Why not? As a formula this is ...
2
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2answers
126 views

Origin of cusps in simulated dark matter halos

I keep reading that cusps are one of the most "robust" predictions of N-body simulations of dark matter halos. But papers I've found on the topic make it sound like these simulations are complicated ...
5
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3answers
1k views

Can we apply Schrodinger equation in Newton Gravitational potential and derive the deterministic Newton's gravitation as a special case of it

We know the solutions for wave functions of a an hydrogen atom, and the energy values as given by spectral analysis of radiation emitted by Hydrogen, confirms the possible energy states as predicted ...
0
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1answer
47 views

Gravitational intensity [closed]

I calculated the gravitational intensity and potential at a point P due to a horizontal linear mass distribution of length '$L$', mass '$M$' and uniform linear density at a distance '$R$' apart from ...
2
votes
5answers
179 views

No need Power to fly ? Paradox [duplicate]

I would like to know how much power I need for magnetic levitation. $$P = Fv.$$ $F = F_g \approx \text{mass} \times 10$, okay. But $v = 0$! I can't believe I need no power to keep an object in the ...
0
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2answers
73 views

Gravity Vs Distance [closed]

What is the relationship between the magnitude of earth's gravity and the distance away from the earth's surface? Or at what rate does gravity decrease as one moves away from earth?
1
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0answers
23 views

Eccentricity of planetary orbits: What information is contained?

I'm having a little trouble understanding what makes a planetary orbit explicitly elliptical. Is it simply that the initial velocity was different from the circular orbit case for a given starting ...
2
votes
2answers
258 views

What would be walking speed in low gravity?

In $1g$ the average adult human walks 4-5 km in an hour. How fast would such a human walk in a low gravity environment such as on the Moon $(0.17g)$ or Titan $(0.14g)$? Let's ignore the effects of ...
2
votes
1answer
90 views

How does the strength of gravity affect human walking speed? [closed]

Walking requires friction and gravity, would humans be able to walk faster in different strength gravitational field than that of earth's? What strength of gravity would allow an average human to ...
4
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1answer
96 views

How “large” is a Lagrange point?

When placing an object at a L-point, the natural assumption, as with all things gravity, is that you needn't place it in an exact spot to achieve a stable configuration. How much room do you have to ...
1
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2answers
59 views

With friction, does the path followed from A to B affect energy transfer?

Consider I have a roller coaster that can travel across one of three paths, all of which are half circles of the same size. The half circle is an arch that starts vertically up, and ends vertically ...
2
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1answer
103 views

How are tidal gravity and curvature related?

I see tidal gravity mentioned in the literature sometimes, and sometimes people even say something like that is the “real gravity”. I am confused about the significance of tidal gravity, and what ...