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Questions tagged [newtonian-gravity]

This tag is for questions regarding the Newtonian model of gravity in which the force between two objects is given by $~GMm/r^2~.$ It is a natural phenomenon by which all things with mass or energy – including planets, stars, galaxies, and even light – attract one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

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Is gravitational potential energy of body by $mgh$ negative?

Consider a 15kg object at 1m from earth ground level, is P.E = 15kg * 9.8m/s^2 * 1m = 147J or P.E = -Gm1m2/r^2 * h = -9.8 * 15kg * 1m= -147J after browsing for a while on debate of potential energy's ...
Neptotech -vishnu's user avatar
3 votes
1 answer
503 views

How accurate does the ISS's velocity and altitude need to be to maintain orbit?

We know the the ISS is not drifting weightless in space, but rather is constantly falling as it circles the Earth. To do this it must be at a specific altitude and moving with a specific velocity. ...
foolishmuse's user avatar
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0 votes
2 answers
82 views

What would happen to the moon's orbit if we reduce (instantaneously) its mass? [closed]

In my opinion the moon's orbit shouldn't change, because an orbiting body is a free falling object and the trajectory of a free falling object is not affected by its mass (because the inertial mass ...
Suppiluliuma's user avatar
1 vote
2 answers
147 views

Doubt on conservation of angular momentum for Kepler's laws

Just before proving Kepler's laws, my Professor claimed that if $\vec{F}$ is a central force with center $O$ and it is the only force acting on a point $P$, then the trajectory of $P$ is a curve plane....
Davide Masi's user avatar
-2 votes
5 answers
105 views

When an object is thrown towards the sky it starts to gain potential energy, why?

I didn't think so because when an object is thrown towards the sky it already has kinetic energy and it looses it's energy due to the gravitational force of the earth. When the object looses all of it'...
Priyanka Bahadur's user avatar
0 votes
1 answer
62 views

Has our knowledge of astrophysics and gravity reached the point where we can accurately calculate Lagrange points?

is it possible for us today given the knowledge we possess of gravity and our success with inserting satellites in to steady/ geosynchronous orbit and any knowledge we have on the relative size (and ...
Matt Bartlett's user avatar
-1 votes
3 answers
42 views

Local vs distant gravity effects where is the boundary line of effective control? [closed]

I'm not one of the 'gravity is only a theory' crowd or a flat earther that thinks gravity is fake and that down is always down. but thinking about gravity and what has been put forward by many great ...
Matt Bartlett's user avatar
30 votes
2 answers
3k views

Error concerning projectile motion in respected textbook?

In the textbook Fundamentals of Physics by R. Shankar of Yale Open Courses, appears the following assertion pertaining to a car driving off a cliff, which seems correct: This is exactly how long it ...
Trever Thompson's user avatar
1 vote
3 answers
75 views

How much time does it take for an object to fall from space? [closed]

Let's say there's an object of mass $m$ in space, $h$ meters away from the surface of the Earth. $h$ is large enough that $g$ cannot be assumed to be constant. The acceleration varies according to ...
jazzblaster's user avatar
-1 votes
1 answer
64 views

How Can there be a Gravitational Potential when there is NO Gravitational Field? [closed]

How does it make any logic that there exist a potential when there is no net field for example when we have a Hollow Sphere with mass we can find out the the gravitational *potential inside the sphere ...
Aditya Agrawal's user avatar
0 votes
2 answers
70 views

Do objects really "fall" at the same rate? [duplicate]

I understand that a hammer and a feather were dropped on the moon and they both landed at the same time. I understand that for all practical intents and purposes all objects do fall at the same rate. ...
user875234's user avatar
2 votes
1 answer
74 views

Gravitational collapse - proof that energy dissipation is required?

As an undergraduate, I took a short course on astrophysics, where I encountered the Jeans mass. This is the critical mass for a spherical cloud of interstellar gas above which the cloud is predicted ...
Martin Vaughan's user avatar
6 votes
6 answers
3k views

Why is pressure in the outermost layer of a star lower than at its center?

I have done the math and I have obtained the hydrostatic pressure in a star is lower at the outermost layer of a star than in its center, where the pressure is actually maximum. Although the equations ...
Lagrangiano's user avatar
  • 1,616
1 vote
4 answers
75 views

Why is work done by force $+mgh$ in the situation of throwing something up?

If there is a particle at point A(at rest) and a force moves it to point B(Above point A vertically)(final velocity = 0 at this point), the work done by gravity is $-mgh$. This I understand as the ...
Gaurav Batra's user avatar
1 vote
0 answers
48 views

Why does an accelerometer read geavity when at rest? [duplicate]

This may sound like a stupid question but why does an accelerometer read 9.8 (gravity) on the vertical axis when I set it down on a table? I have just finished AP Physics Mechanics and was under the ...
Frontiers Aerospace's user avatar
4 votes
4 answers
343 views

What is the relationship between gravitation, centripetal and centrifugal force on the Earth?

I'm trying to analyze a situation wherein a ship is moving across the surface of the earth. I am trying to analyze this situation in a reference frame that is rotating with the earth (NED frame). I am ...
john morrison's user avatar
0 votes
0 answers
51 views

Rocket equation non-constant gravity

I am currently trying to teach myself differential equations and wondered about the following problem. You have an object (a rocket of constant mass $m_r$) and initial velocity $v_0$ that tries to ...
Imago's user avatar
  • 253
2 votes
1 answer
43 views

Trajectories of projectile based on different speeds of projection [duplicate]

So my teacher was teaching gravitation and an interesting fact that he mentioned was the trajectory of a projectile projected from Earth at a speed equal to escape velocity, is parabolic. Also, he ...
NPC's user avatar
  • 21
0 votes
1 answer
80 views

Where am I wrong in proving that force perpendicular to motion increases speed and kinetic energy? [closed]

Lets think of a helicopter flying at some height $h$. It throws a food packet to a person on the ground from air. Let's neglect the air drag. The food packet is thrown only with some velocity $v_x$ in ...
Gaurav Batra's user avatar
0 votes
1 answer
40 views

Integrating acceleration + escape velocity over distance [closed]

I am not sure how to title this question so apologies if it's inaccurate. If I throw an object at thrice the escape velocity of earth, what would be its velocity very far away from earth, (at a ...
uggupuggu's user avatar
  • 129
0 votes
3 answers
81 views

Pseudo Orbital motion only due to Coriolis force

Planet, say of mass M and radius R is rotating with some angular velocity ω and a object of mass m (initially on the surface and rotating with the planet) was launched with velocity v vertically ...
Kyathallous's user avatar
1 vote
2 answers
78 views

The topology of planets [duplicate]

Just a curiosity: Let $g \in \mathbb{Z}_{>0}$. Is it possible for a planet of topological genus $g$ to exist? For example, is there any contradiction (from the point of view of physics) in assuming ...
numberwat's user avatar
  • 121
0 votes
0 answers
30 views

Better equations for modeling and simulating a halo orbit?

I'm trying to model a halo orbit at low altitude (10m from surface). The satellite is using propulsion to trace the circular halo path. It looks like this "from the top" (the blue ball is ...
Nico Brenner's user avatar
0 votes
0 answers
31 views

Restricted 3-body: one large mass and two smaller ones

A restricted 3-body problem is usually understood as two large bodies and one much smaller one that doesn't affect the motion of the other two. I am curious about a 3-body problem with one large body, ...
0 votes
1 answer
75 views

When two objects collide, which directions do they go in after the collision?

I am watching this video here: https://www.youtube.com/watch?v=KPhMMnIocR0&list=PL4VRaRxeNj-1F-JukcRVAzbiIi0ibrHqy. At 11:02, the author shows a simulation and says that for a Galton Board (https:...
bula's user avatar
  • 11
1 vote
1 answer
48 views

Drawing a free-body diagram for a body residing on Lagrange point $L_4$ and $L_5$

I am aware of the fact that Lagrange points $L_4$ and $L_5$ are stable equilibrium points however I cannot understand why they are equilibrium points in the first place. Consider a Earth-Moon system ...
John Davies's user avatar
0 votes
1 answer
57 views

When is it appropriate to say Newtonian gravity is a force? When is it not appropiate? [closed]

Please help me understand the notion of force when it is applied to Newtonian gravity. From my understanding forces in physics involve interactions with at least 2 objects and can cause an ...
Qubit's user avatar
  • 431
3 votes
1 answer
112 views

Confusions on The Gravitational Energy of a Point P in a Cube

I have been working, quite tirelessly, to try and find an answer to a question that has been bothering me for some time now. I have been working over some proofs, in the Newtonian Mechanics world, to ...
Statico's user avatar
  • 152
6 votes
7 answers
1k views

What changes the velocity perpendicular to radius in an elliptical orbit?

I'm working currently on a problem that asks to justify that angular momentum and kinetic energy conserves for a planet in an elliptical orbit. Although I've been taught that angular momentum should ...
RChen's user avatar
  • 69
-5 votes
1 answer
66 views

Can the $r^2$ in gravity be seen as signifying the distance of object 1 to 2 times distance from object 2 to 1 [closed]

If the formula for gravity multiplies the mass in the numerator and the distance in the denominator is this akin to saying the multiplied masses over the multiplied distances times the gravitational ...
OJN's user avatar
  • 1
0 votes
0 answers
44 views

Is there a deeper relationship between symmetry and gravitational potential comparing Newton's and Einstein's gravity?

In this question, see Why is general relativity in (2+1) dimensions different from cylindrical systems in (3+1) dimensional GR?, it is mentioned "The gravitational potential Φ of an infinite rod ...
timm's user avatar
  • 1,589
5 votes
1 answer
302 views

EM 4-potential vs gravity 4-potential?

In classical field theory, the electrostatic and gravitational fields have very similar differential forms: $$\vec \nabla\cdot \vec{E}=\frac{\rho}{\varepsilon_0}$$ $$\vec \nabla\cdot \vec{g}=-4\pi G\...
Lagrangiano's user avatar
  • 1,616
0 votes
1 answer
41 views

Dual of Newtonian gravitational field

In the static state, the laws of Newtonian gravity and Coulomb force have exactly same formulas, $$F = K \frac{A_1A_2}{r^2}.$$ In the electrical case, moving materials produce a field, say a dual ...
moshtaba's user avatar
  • 1,409
0 votes
2 answers
82 views

Why are planets denser as you approach the center?

Gauss' law says that the net electric force inside a hollow, uniform, not rotating sphere is zero. Since gravity is also proportional to the inverse square of the distance, I assume this should apply ...
Joseph Hirsch's user avatar
3 votes
2 answers
340 views

Why are forces superimposable in Classical Mechanics? Does this also apply in higher theories like General Relativity and Quantum Mechanics?

In classical mechanics, forces are treated as vectors and are added linearly. Is this principle to be treated as an axiom or is there some underlying principle from which this is derived? And given ...
Vivek Kalita's user avatar
2 votes
4 answers
187 views

Is the gravitational potential energy of an object on the ground 0? [duplicate]

In class, we were reviewing kinetic and potential energy and my teacher claimed that on the ground, objects have potential energy. However, as they cannot fall further, isn't their gravitational ...
user386598's user avatar
0 votes
1 answer
61 views

Find eccentricity of orbit given the velocity and the semi-major axis

Is it possible to calculate eccentricity of orbit knowing only the semi-major axis and the velocity of both celestial bodies? If not, what other additional information is required. Does the fact that ...
Sid N's user avatar
  • 38
1 vote
4 answers
160 views

Gravitational attraction between two bodies

While the gravitational force between two bodies is directly proportional to their masses, and inversely proportional to the distance between them is understandable / seems logical, how did Newton ...
Niranjan's user avatar
  • 123
1 vote
2 answers
28 views

Gravitational attraction between two bodies and gravitational accelaration [duplicate]

Since Newtons laws on gravity state that the gravitational attraction between two bodies is directly proportional to their masses and inversely proportional to the square of the distance between them, ...
Niranjan's user avatar
  • 123
2 votes
0 answers
37 views

When are two object guaranteed to keep getting further and further away?

In a two-body problem, it is known (if I understand correctly) that if the specific orbital energy of the system is $\varepsilon \geq0$, then the objects must eventually escape each other. My question ...
Remeraze's user avatar
  • 125
0 votes
0 answers
14 views

Describing force accumulation trend of an infinite volume with evenly distributed radiative sources

I am looking for confirmation if I've built my equation properly. My goal is to describe the change in force over time at a given point if evenly distributed radiators (in-phase or cumulative energy/...
WhetScience's user avatar
1 vote
1 answer
63 views

Quantised Newtonian potential as an operator in non-relativistic QM [closed]

Suppose we have two slowly moving (effectively static) masses $m_1,m_2$, interacting through gravity, that are not occupying a definite state of position i.e. that matter is being treated quantum ...
Theoreticalhelp's user avatar
14 votes
4 answers
10k views

If gravitation is negligible for small masses, how was Cavendish's experiment successful with balls much smaller than celestial objects?

If gravitation is negligible for small masses, then how was Cavendish's experiment a success since the balls used were very small compared to the sizes of celestial objects?
JAYANT SINGH GBPP's user avatar
0 votes
1 answer
48 views

Would an Hypothetical Ringworld Positioned Inside the Moon's Orbit Around Earth, gravitationally affect Earth?

If a ringworld were to encircle Earth within the orbit of the Moon, would it induce any gravitational alterations on Earth? I grasp that inside a circular structure, there might not emerge a ...
wepajakeg's user avatar
1 vote
2 answers
56 views

Does the distance between two objects of mass not matter when measuring strength of gravity in one-dimensional space?

From all that I have heard about Newton's Law of Universal Gravity, one fact, which I find quite interesting, is that the distance between the two objects of mass is squared and not cubed due to our ...
Quantum Wonder's user avatar
0 votes
2 answers
82 views

Initial positions and velocities for the three-body problem

I have made a simulation of the three-body problem, it follows the euler's method of solving differential equations. I have tried some initial positions and velocities of the bodies and have observed ...
Ronny's user avatar
  • 166
1 vote
0 answers
42 views

Einstein's equation of gravitation field [duplicate]

I'm looking for the reason why there is the number eight $8$ at the r.h.s. of EI: $$R_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}=\frac{8\pi G}{c^2}T_{\mu\nu}.$$ My attempt was to take the limit of this equation ...
user2925716's user avatar
0 votes
1 answer
21 views

Can we treat the entire mass of the spheroid as being concentrated at its center?

I know that to find the gravitational force between two objects, if either of them is a sphere, we can assume its mass to be concentrated at its center and use the formula for gravitational forces for ...
Peter swift's user avatar
0 votes
1 answer
61 views

Deriving expression for gravitational potential energy around a mass, $M$, using vectors

(I think my question will be somewhat related to this one: Deriving gravitational potential energy using vectors .) I know the change in the potential energy associated with a conservative force, $\...
Anis Manuchehri-Ramirez's user avatar
0 votes
1 answer
48 views

Speed of satellite in elliptical orbit [closed]

A satellite $S$ orbits a planet of mass $M$ in an elliptical orbit. At perihelion, $S$ has a tangential velocity of $v_1$ and is distance $r_1$ from the planet. At aphelion, $S$ has a velocity of $v_2$...
asdf's user avatar
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