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Questions tagged [newtonian-gravity]

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

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Proportional acceleration due to changing density of the Earth

My question has to to do with a recent video Minutephysics posted about the time it takes for a person to fall through the earth, found here http://www.youtube.com/watch?v=urQCmMiHKQk At around 4:05,...
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1answer
149 views

Pendulum at an angle [on hold]

A pendulum has a period of $T$ when swinging from a string. The pendulum is now placed on a frictionless incline at a 30 degree angle. What is the new period of the pendulum?
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37 views

Why do 2 objects, when dropped, reach the ground at the same time? [duplicate]

2 objects of the the same volume and dimensions but with different weights are dropped from a sufficient height in which said objects can reach terminal velocity. Galileo's finding was that both ...
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11answers
50k views

Don't heavier objects actually fall faster because they exert their own gravity?

The common understanding is that, setting air resistance aside, all objects dropped to Earth fall at the same rate. This is often demonstrated through the thought experiment of cutting a large object ...
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4answers
1k 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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2answers
54 views

What's the nicest proof that two isolates masses orbit their center of mass? [duplicate]

Although it seems intuitive, I haven't found proof of this fact in my textbooks from a purely mathematical standpoint. I was wondering if anybody knows of a particularly elegant proof of this fact, ...
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2answers
567 views

Is the Moon's Speed Greater than the Earth's?

Is the moon's speed greater than Earth's? I thought about this for a bit and I believe it to be so. The moon has a certain speed from its orbit around the Earth. Let's call this x. The Earth has a ...
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0answers
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Formula for horizontal compression caused by tidal acceleration [closed]

I understand how tidal acceleration separates objects falling vertically into a gravitational field. This has been covered many times and derived nicely here. $$\Delta F = 2G \frac{Mm}{r^3} \Delta r.$...
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1answer
52 views

Where is the location of centre of gravity of the Earth? [on hold]

Take the Sun as a point object at the origin. Take the Earth as a sphere centred at $x=d$ with a radius of $R$ Let $d=150,000,000,000$ m Let $R=6,400,000$ m Slice the sphere into vertical disks of ...
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2answers
387 views

What is the difference between orbital velocity and critical velocity? Are their values similar or not?

As critical velocity is the minimum velocity required to put a satellite into orbit. And orbital velocity is the velocity required to keep a satellite moving in an orbit.The value of critical velocity ...
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3answers
567 views

Bending of light - photon's inertia instead of mass

Using classical mechanics, the formula for gravitational attraction is $$F = G\frac{m_1m_2}{r^2}.$$ This formula does not work for photons, and we need to use Einstein's theory of gravity to ...
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1answer
43 views

Formula for would something fall over or not?

Let's say I have a 10cm x 10cm x 50 cm wooden stick that weights 5kg total. The 10cm x 10cm base is touching the floor and it protrudes from the floor 50cm which is the height of the stick. Based on ...
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1answer
3k views

Does gravity have any effect on sound waves? [duplicate]

If gravity at a place increases or decreases, does it affect the sound wave propagating through that place. If for certain place gravity increases on earth will there be change in direction or ...
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3answers
146 views

Is it possible to build planet-sized non-spherical structures?

Beyond certain size and density the celestial objects tend to admit a spherical size. I wonder if is there a fundamental mass, density or specific strength related number which when surpassed a non-...
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0answers
45 views

Derivation of gravitational field intensity of an elliptical disc about its symmetry axis [closed]

Please help me to derive the gravitational field intensity of an elliptical disc about its symmetry axis by using the gravitational field intensity of an elliptical ring. Please don't close this ...
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3answers
233 views

Is gravitational acceleration truly independent of mass?

I am doing Newtonian Physics. Correct me if I am wrong: So two objects always exert equal forces on each other(Newtons Third). So for example the same gravitational force that the earth exerts on a ...
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1answer
44 views

Why doesn't the Earth slowly collapse into the Sun? [duplicate]

I understand that the sun exerts a force on the earth and that if that was the only force exerted on the earth then the earth would have already crashed into the sun a long time ago. The reason the ...
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2answers
31 views

Gravitational force on point mass due to uniform rod

So we have a uniform rod of mass M and length L and we have placed a point mass of mass m, which is distance a away from the midpoint of the rod. Now setting the coordiates axes to work with, I put ...
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2answers
63 views

A few questions on Gravity [closed]

What role does the unit vector $ \mathbf{e}_r $ play in $$ \mathbf{F} = - G \dfrac{Mm}{r^2} \mathbf{e}_r$$ and why there's a negative sign? If the gravitational force always acting in the same ...
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2answers
49 views

Constant gravitational acceleration $g$ and energy

I've been taught that $g$ is constant for different masses and that if I were to drop a heavy object and a light object from the same height then they would reach the ground at the same instant with ...
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1answer
52 views

Human Body Upward Acceleration on Scale [closed]

I am reviewing for a Physics exam, and have come across the following example question: If I weigh 200 pounds, but a scale I'm standing on reads 400 pounds, then I am accelerating upward at 1g 2g 3g ...
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0answers
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Partition function of an asteroid gas (gravity)

Consider the classical problem (Newtonian gravity) of a large number of $N$ identical non-interacting asteroids orbiting around a big planet. I wanted to see if the problem was solvable. I wrote my ...
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9answers
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Are we slightly lighter during the day and slightly heavier at night, owing to the force of the Sun's gravity?

Using $g = \frac{Gm}{r^2}$, the force on a point mass located at 1 AU from the Sun ($m = 2 \cdot 10^{30} \text{ kg}$) is about ~0.006 N/kg. Does that mean that, e.g., a 70 kg person is ~42g lighter ...
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0answers
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Large mass body on Lagrange point L4/5

Lagrange points L4 and L5 are stable for a test particle. But what happens if instead the body at L4/5 (let's call it C) has a mass significant enough that its gravitational pull on the other two (let'...
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5answers
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What is Difference between Acceleration due to Gravity and Gravitational Field Intensity?

I have read that gravitational field intensity and acceleration due to gravity are two different physical quantities that have the same direction, magnitude, and units. So, if all the units, ...
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1answer
168 views

Climb a rope down to Earth?

How long would a rope if possible have to be to stand up right lowered from space but stationary tethered on the ground in a Geo synchronous orbit? Would the difference in gravity and stress on the ...
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5answers
3k views

Why is escape velocity necessary if a rocket can just move up slowly? [duplicate]

I have read multiple explanations of escape velocity, including that on Wikipedia, and I don't understand it. If I launch a rocket from the surface of the Earth towards the sun with just enough force ...
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2answers
103 views

Weight of mass falling through liquid

If I place a container of fluid on a scale and drop a non-buoyant mass into the fluid, will the scale read less as long as the mass is in motion downward as compared to when the mass is at rest on the ...
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4answers
113 views

Kepler's third law is unintuitive

Kepler's third law states that the ratio between the period of a planet in orbit round a star squared over the average distance to that star cubed, is constant. And in the case of an elliptical orbit, ...
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3answers
95 views

If there was a hole in the north pole to the South Pole and you jumped into it how would would you come out feet first? [closed]

If I were to dig a hole in a round sphere Say the earth starting at the north pole standing on my feet I start to dig when I come out the other side would I come out of the whole feet first or head ...
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1answer
54 views

How to reach $U = mgh$ Using Newton's Law of Universal Gravitation? [duplicate]

today i was curious about the potential energy, so, i started studying the Newton's Law of Universal Gravitation which its equation is \begin{eqnarray} U= -\frac{GMm}{r}.\end{eqnarray} Well, since i ...
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2answers
90 views

Gravity Assist Analogy

I'm having tremendous difficulty accepting the reality of this phenomenon. I have read countless analogies of balls hitting trains and moving walls, etc but I still cannot reconcile why the rebounding ...
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3answers
203 views

Does the gravitational field possess an inertial mass? [duplicate]

I understand that inertial mass, at least in part, comes from the inertia of energy in the zero momentum frame or rest frame of some physical system. So for a static charge the corresponding field ...
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0answers
26 views

Physics behind finding center of mass of a stick like object [duplicate]

If I hold a rod with both hands wherever at opposite sides of the center of mass of the body, and bring them slowly close to each other, then the point my hands meet at, is approximately the center of ...
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1answer
35 views

Is gravitational force different from centripetal force in projectile motion?

This has always confused me, in a projectile motion, like a cannon shooting an object, the only force acting on the body is gravitational force, which is facing downwards or more precisely, ...
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0answers
30 views

Does dark matter experience drag?

Is dark matter dragged around the galaxy by gravity as stars and groups of stars orbit the galaxy, and, if so, is its shape/distribution deformed? Similarly, would the Oort cloud be deformed by being ...
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3answers
63 views

Proving that gravitational potential is work done by the object against gravity while KE increases and PE reduces

There's a person in my class who thinks that the formula for gravitational potential (-GM/r) represents the work done by gravity to move an object from infinity to any point in the gravitational field....
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1answer
2k 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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0answers
43 views

What would happen if I used a jet pack that accelerates at $g$ but always upward?

I'm trying to imagine what would happens if gravity is cancelled. I assume that without air, if the effect of gravity were to disappear I would fly off Earth on a tangential line. But with the air ...
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1answer
193 views

How can the properties of the Earth be determined?

How can the properties of the Earth be determined? And how is the gravitational constant then determined from them? A satellite can determine the G.M.. But, how they are individually determined ...
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1answer
33 views

Determine corner weights of a trapezoid

Working with determining the corner weights on one axis isn't too bad. If A is to the left of the Center of Gravity and B is to the right of the Center of Gravity. You have two equations to work with....
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2answers
59 views

When would an object not be considered a point-particle in relation to gravity?

When is the Earth, for example, not considered a point in relation to gravity? I am thinking that if one was asking a question below the crust continously to the core, then this would be an example. ...
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2answers
62 views

Is a *difference* of potential energy relative to a frame of reference?

If we consider an electrical field, or a gravitational field, and two points in this field, is the difference of potential between this two points depending of a frame of reference ? It seems to me ...
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4answers
4k views

Potential energy sign conventions

Almost every book on physics that I read have some weird and non-clear explanations regarding the potential energy. Ok, I do understand that if we integrate a force over some path, we'll get a ...
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2answers
81 views

Which fundamental force underlies inertia? [closed]

We learn about the four fundamental forces (gravity, electromagnetism, strong, weak). I am curious about how these four forces mediate/cause/drive everyday phenomena. In particular, it has never been ...
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0answers
25 views

gravitation (kinetic energy and angular momentum)

When a satellite in a circular orbit around the earth enters the atmospheric region it encounters small air resistance to its motion. then (1) kinetic energy increases (2) angular momentum decreases ...
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3answers
83 views

Newtonian gravity equation / Big $G$; not duplicate from search results

EDIT: I apparently need to rewrite this from the RE's, but I'll leave it for continuity sake. Please read my replies for my point/question clarifications. There are several threads regarding big G ...
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2answers
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Where is the center of mass of earth?

No. I am not asking for the center of Earth's map. On average, the kg/m3 of Earth's soil is heaver than the kg/m3 of oceans, and the earth does not have a flat surface. And as we have quite some ...
2
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1answer
432 views

Newton's theory of gravity is covariant under Galilean transformations

We know from classical mechanics that the gravitational field equation for the scalar potential takes the form $$\nabla^2\phi=4\pi \rho,$$ where $\rho$ is mass density (which, can depend on time and ...
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2answers
85 views

Mass hanging from spring in free fall

Q: A mass $m$ hangs from a massless spring connected to the roof of a box of mass $M$. When the box is held stationary, the mass-spring system oscillates vertically with angular frequency $\omega$. If ...