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? [closed]
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 ...
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How do you derive the compound pendulum formula?
How do you derive $$T=2\pi\sqrt{I/mgl},$$ where $I$ is the moment of inertia and $l$ is the length of the pendulum?
Is it even the right formula? How would I derive a compound pendulum formula for a ...
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Why is potential energy negative when orbiting in a gravitational field?
I had to do a problem, and part of it was to find the mechanical energy of satellite orbiting around mars, and I had all of the information I needed. I thought the total mechanical energy would be the ...
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Does an object falling from very large height as compared to radius of Earth rotate as well due to gravity?
If let us say a rigid body is falling from a height such that value of $g$ remains same then the body does not rotate at all about the centre of mass as centre of mass and gravity coincide hence net ...
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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. ...
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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 ...
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Interpretation of gravitational potential in 2+1D
From Gauss's law of gravity reduced to 2+1 dimensions, one can easily show that the gravitational force follows an inverse law, i.e.
$$
\mathbf{F}(\mathbf{r}) =- \frac{G m M}{|\mathbf{r}|}\hat{\mathbf{...
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Does Earnshaw's theorem apply to electrostatic + gravitational systems?
I've been learning about particle traps and Earnshaw's theorem. When dealing purely with electrostatic forces the theorem makes intuitive sense to me. But does it really apply to systems involving ...
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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'...
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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....
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Why are fields described as force divided by mass or charge?
I have read that application of force on a body from a distance, like gravitational or electrostatic force is a two-step process, first, the field is created by the body, then, the application of ...
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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 ...
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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 ...
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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 ...
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From my reference frame, why does the Earth need a huge kinetic energy [$0.5M_E(11200)^2=3.75*10^{32}$ joules] to escape me? [closed]
I wake up screaming into the void, when I see the Earth almost touching me but going away from me at 11.2 $km/s$.
I don't remember what happened before I woke up. I faintly recollect being cannoned up ...
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Why should Apparent weight of the object floating in a fluid is 0?
The buoyant force act on the object and weight of the body act on water, so do they both cancel out?
Now one more thing weight experienced by a body is equal to reaction force acting on a body so here ...
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Generalization of Feynman's derivation of the formula for gravitational potential energy in FLP volume I
In the Feynman Lectures on Physics, Feynman derives the formula for gravitational potential energy by applying a line of reasoning he borrowed from Carnot on reversible weight lifting machines (FLP I, ...
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Work done by conservative and non-conservative forces
Work done by conservative forces changes one form of mechanical energy into another. Is it correct to assume that work done by non-conservative forces changes one form of energy to another, for e.g., ...
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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 ...
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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 ...
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Intuition behind gravitational potential
Gravitational potential at a point is equal to work done in bringing a unit mass from infinity to a particular point
That was the text book definition
$$V_{p} = -\frac{GM}{r}$$
If we calculate $V_p$ ...
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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 ...
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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 ...
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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.
...
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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 ...
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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 ...
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Two particles rotating about their center of mass
Two bodies each of mass $m$ are rotating about their center of mass where the radius is $r$.
Here centripetal force of each body is $\frac{mv^2}{r}$ where $v$ is the linear speed. Now, gravitational ...
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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 ...
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How does gravitational potential energy work in a very large distance?
Consider a thought experiment (that I made when I was in high school) involving a universe with only two objects: a massive planet and a small asteroid. Initially, they are millions of light-years ...
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Work done to raise an object in two sample cases
I know that gravity does a work of an amount equal to $MGH$ because a more formal definition of work $W$ done by a net force $F$ is $$\int_a^bF(x)dx$$ where $F(x)$ is the net force acting on a ...
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Regarding the objects in free fall in the ISS
There are lots of information about this topic, but I'm still greatly confused about something:
Astronauts in the ISS are in free fall all the time because they have only gravity acting on them, but ...
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Tidal forces between Moon and Earth
I started studying about gravitation recently and I came across the fact that when finding the gravitational force between the earth and some point mass in space, we can consider the mass of the earth ...
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Angular momentum of the center of mass of yo-yo reaching the end
I am a physics undergrad, and I know only a basic stuff about the subject.
Yesterday, I was taught about the angular momentum of a yo-yo and
my professor said that when the yo-yo hits the end of the ...
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Rocket equation non-constant gravity
I am currently trying to teach myself differential equations and wondered about the following problem.
You have an object (a rocket of constant mass $m_r$) and initial velocity $v_0$ that tries to ...
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Where am I wrong in proving that force perpendicular to motion increases speed and kinetic energy? [closed]
Lets think of a helicopter flying at some height $h$. It throws a food packet to a person on the ground from air. Let's neglect the air drag.
The food packet is thrown only with some velocity $v_x$ in ...
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Question about Lagrange's solution for the three-body problem
The original text in my textbook, written in short:
"By Newton's second law,
$$\ddot{\mathbf{x}}_1=-Gm_{2}\frac{\mathbf{x}_1-\mathbf{x}_2}{|\mathbf{x}_1-\mathbf{x}_2|^3}-Gm_{3}\frac{\mathbf{x}_1-...
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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 ...
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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 ...
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Projectile/orbital motion over very long distance
We know the optimum angle for greatest horizontal displacement when launching an object with projectile motion is 45 degrees.
How to solve the angle when it is real long distance around the earth ...
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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 ...
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The impossibility (or possibility) of solving $N$-Body problem
One can obtain the solution to a $2$-Body problem analytically. However, I understand that obtaining a general solution to a $N$-body problem is impossible.
Is there a proof somewhere that shows this ...
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What is the gravitational force acting on a massless body?
It's a well known fact that acceleration due to gravity is independent of the mass of the accelerating body, and only depends on the mass of the body it is accelerating towards and the distance from ...
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Gravitation in a Toroidal Planet
I recently took interest in toroidal planets, not because they necessarily exist, but rather due to a more practical result (it can be easily represented with a rectangle). This got me curious about ...
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Toroidal Planets
I have read online in numerous places about the possible existence of toroidal planets, and I most people seem to believe that they could exist, but they also have no evidence to support this claim. I ...
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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 ...
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Infinite acceleration of bob in pendulum with no friction or air resistance
So i'm a bit confused about something. If we take a mathematical pendulum and we apply a force to it. We ignore all friction and air resistance and only consider gravity and the force applied to bob. ...
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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 ...
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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, ...
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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:...
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Does 'special relativity + newtonian gravity' predict gravitational bending of light?
It seems to me that special relativity (SR) already predicts that gravity will bend light rather than this effect being a proof of general relativity (GR). Photons have energy proportional to their ...
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