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

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How does the earth move?

My son who is 5 years old is asking me a question about how the earth moves around the sun. What answer should I give him?
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5answers
876 views

How much does the Earth's rotation affect a golf ball?

When launching rockets into space, they start straight but begin to lean, I assume due to the Earth's rotation. For something on a much smaller scale, such as a golf tee, is there a measurable ...
4
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3answers
87 views

What is an intuitive explanation using forces for the equatorial bulge?

The earth is not a sphere, because it bulges at the equator. I tried fiddling with centripetal force equations and gravity, but I couldn't derive why this bulge occurs. Is there (a) a ...
2
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1answer
125 views

What are the determining factors for the velocity of orbiting bodies?

Please bear with me, as I'm not in the field of physics, this question may seem a bit simple. The scenario is the following; A specific stable orbit radius of a small body, say a satellite, to ...
12
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2answers
394 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 ...
0
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1answer
62 views

Kinematics and Energy - Finding the work done in projectile motion

If you are asked to find the work done by gravity on a projectile, the force will obviously be the mass multiplied by gravitational acceleration. What will the displacement be, the horizontal or ...
0
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1answer
34 views

Gravitational effect of charged masses held apart by a rod?

Imagine two oppositely electrically charged masses held apart by a rigid rod of negligible mass. At some distance the gravitational field due to this system is proportional to the sum of the masses + ...
5
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3answers
477 views

Gravitational force of the Earth [duplicate]

Why does gravitational force of the Earth decrease as we move towards the centre of the Earth? Where as inverse square rule says that distance is less than gravitational force is more.
52
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4answers
6k views

Moon's pull causes tides on far side of Earth: why?

I have always wondered and once I even got it, but then completely forgot. I understand that gravity causes high and low tides in oceans, but why does it occur on the other side of Earth?
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0answers
89 views

Has this approach to Coulomb force/Newton gravity unification ever been published?

Introduction: When toying with gravitational and electromagnetic equations in my undergrad days I stumbled upon this interesting relationship. With the very childish hopes of unifying gravitation ...
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0answers
26 views

Any way to Find the Position Function of a body under gravitational force?

Here's the problem I am trying to find a solution to: Consider a heavy point particle of mass $m_2$ fixed at a point (preferably the origin) and another light point particle of mass $m_1$ at an ...
3
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3answers
126 views

How many celestial bodies could be in stable orbit at roughly the same distance from a star?

How many planet-like celestial bodies of roughly the same mass (say within 50%) could orbit a star at roughly (say within 10%) the same distance from the star and be in stable orbits. By stable I ...
9
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1answer
369 views

Gravitational Constant in Newtonian Gravity vs. General Relativity

From my understanding, the gravitational constant $G$ is a proportionality constant used by Newton in his law of universal gravitation (which was based around Kepler's Laws), namely in the equation $F ...
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3answers
888 views

Projectiles and escape velocity [closed]

Q: The escape velocity for a body projected vertically upwards from the surface of earth is 11 km/s. If the body is projected at an angle of $45^\circ$ with vertical, the escape velocity will be? ...
0
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1answer
55 views

Does gravity act in the centre of the Earth? [duplicate]

If we we dig a hole from north pole to the south pole of the Earth and we throw a ball in this hole where would it stop? Will it come back on the surface or it will stop at the centre?
3
votes
2answers
113 views

What does an applied force on an already accelerating object do?

I'm a big beginner having only taken Grade 11 high-school physics. Imagine this situation: an object is accelerating north, and while it's accelerating, it's 'hit' by a northward force. To me it ...
0
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3answers
148 views

Didn't anybody see an apple falling before Isaac Newton? [closed]

We all know that Isaac Newton developed the gravitational theory (as is often told) when an apple fell on his head. But my question is, didn't anyone before him notice it?
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6answers
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Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
4
votes
1answer
108 views

Newton's original proof of gravitation for non-point-mass objects

Suppose we have two bodies, one very large (Earth), and one very small (a cannon ball). If the cannon ball is some distance away from the Earth, to find out the force produced on the cannot ball, we ...
4
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4answers
2k views

Does mass affect speed of orbit at a certain distance?

Does the mass of both the parent object, and the child object affect the speed at which the child object orbits the parent object? I thought it didn't (something like $T^2 \approx R^3$) until I saw ...
3
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0answers
30 views

Does light escape from highly dense bodies [duplicate]

If it were possible to launch a projectile at the speed of light from a body with the mass equal to that of our sun but a density such that its escape velocity was the speed of light how far would it ...
0
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3answers
122 views

What will happen after escaping earth's gravitational field?

Suppose that I escaped the gravitational field of earth. Then: am I going to be pulled by Sun's gravity?
0
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1answer
42 views

Quick question on derivation of mass of star

How do I show that for a binary star system, if one star has mass $M_s$, speed $V_s$, period $P$, the mass of the other star is given by: $$M_P^3 \approx \frac{V_s^3}{2\pi G} PM_s^2$$ I showed it ...
4
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3answers
219 views

Does gravity cause Archimedes' principle and how?

Why do lighter objects float and denser sink? I understand this from the perspective that if the object can displace the equal mass of water it will float, but I wonder from the perspective of ...
0
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3answers
72 views

Solving for Normal Force

I'm working through The Nature of Code, which is an awesome book, lots of fun. I've come across Exercise 3.13 and I'm not sure how to solve it. I'm assuming that the force of gravity and the force of ...
3
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1answer
155 views

Can a very small portion of an ellipse be a parabola?

We consider that when a body is projected from any height from the earth surface with a speed lesser than the orbital speed ( tangentially to the earth surface at that point.) it follows an elliptical ...
3
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2answers
94 views

Does the opening angle of the cone matter?

When discussing orbital mechanics, you learn that all orbits roughly follow an ellipse which is obtained as the intersection of a cone with an inclined plane, creating conic sections. Below is a ...
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1answer
1k views

What would it be like if we had a planet very close to us?

My desktop background rotates through a bunch of space and nature scenes, and this one came up. What would be the effect on people walking around down here, if another earth was looming overhead ...
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0answers
36 views

Can we design the orbit of a satellite with Einstein’s curved space?

I think that the most successful theory of gravity is that the orbit of planet can be explained with this theory and the orbit of satellite was designed with this theory. To design an orbit of a ...
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3answers
42 views

In this particular problem: Is the mass of the system the mass of the person?

I am doing this problem: The upward normal force exerted by the floor is 620 N on an elevator passenger who weighs 650 N. What is the magnitude of the acceleration? This is how I solved ...
0
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1answer
59 views

Square Cube Law?

I've heard about something called the square cube law. What is it? All I know of it is that it has something to do with mass of large objects and their gravitational influence.
0
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1answer
66 views

How the gravitational constant $G$ is determined?

We know the gravitational constant is $G=6.67545 \times 10^{-11} m^3 kg^{-1} s^{-2}$. But how this value is determined at first?
-3
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1answer
196 views

Throwing an object in the air [closed]

Studying formulas about velocity and acceleration I came up with a question: if I throw an object in the air with a velocity $v_0$ (suppose i throw it vertically) in how much time its final velocity ...
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0answers
102 views

Application of trigonometry to the slingshot effect/gravity assist

I have been trying to understand the formula $$v_f^{2}=v_i^{2}+2V(V(1-\cos\beta)+v_i(\cos(\alpha-\beta)-\cos\alpha))$$ as it relates to Fig. 2 on page 5 of this exposition: ...
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1answer
49 views

Finding at a distance from the Earth speed of satellite [closed]

A satellite at 8000 km from Earth where gravity is 6.4 m/s^2. What is the velocity of satellite? I don't the formula to find speed of satellite.
1
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1answer
84 views

Inward Pressure of Gravity

We are looking at White Dwarfs in Quantum and specifically how they are stabilized between gravitation pressure inwards balanced by the Fermi pressure due to electrons. To start the problem off ...
7
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1answer
513 views

Gravitational force from spherical shell

Say we have a point mass $\mu$ located at $(0,0,R)$ and a spherical shell (not considering it's volume!) of radius $R$ located in the origin. So we have a particle standing right on top of the sphere ...
4
votes
1answer
33 views

Galaxy velocity curve

When deriving the relation between velocity of a star and its distance $r$ from the center of the galaxy, one assumes that the masses outside $r$ have no contribution and those inside $r$ give a force ...
5
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3answers
497 views

Derivation of Kepler's laws

How can analytically be derived the Kepler's laws? I found some extremely synthetic equations which from the Newton's laws (in particular $\mathbf{F} = m \mathbf{a}$) tried to obtain the Kepler's ...
5
votes
2answers
1k 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 ...
1
vote
1answer
55 views

Help for orbits of planets

Suppose that an asteroid) that moves at a velocity $v$ passes near to a planet: now I know that the gravity force of the planet will curve the trajectory of the asteroid so I tried to make a draw of ...
7
votes
1answer
102 views

Is $4 \pi G$ the true most fundamental gravitational constant? [closed]

Newton's law of gravitation is: $$F = G m_1 m_2 \frac{1}{r^2}$$ It looks simple and natural. But that's only in 3 dimensions. Let's look what happens in $n$ dimensions: $$n=2 : F = 2 G m_1 m_2 ...
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0answers
20 views

Relation between Earth's rotation-gravity and moving object on Earth [duplicate]

This might be silly question. It's about the rotation of the Earth and the objects moving on it. If I jump into the air, why did I also move with the Earth though I am in the air? I am supposed to be ...
8
votes
12answers
2k views

Is the distance between the sun and the earth increasing?

M = mass of the sun m = mass of the earth r = distance between the earth and the sun The sun is converting mass into energy by nuclear fusion. $F = \frac{GMm}{r^2} = \frac{mv^2}{r} \rightarrow r ...
2
votes
3answers
76 views

Question about (complex) motion of Moon

In an ideal situation, we can use a simple formula to determine the velocity at which a body revolves around a massive body at a particular distance. I was wondering if there is an intuitive way to ...
2
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0answers
93 views

Only gravitation and Newton's $2^{\mathrm{nd}}$ law needed to derive Kepler's laws?

It is known that Kepler's laws of planetary motion can be derived from Newton's laws of motion and his law of universal gravitation. However, are all of Newton's laws of motion necessary? According ...
4
votes
1answer
111 views

Tidal force of Sun?

As I understand, satellites and the Moon orbiting Earth are in free fall. Isn't the same true for Earth orbiting the Sun? My question is then: How can the Sun's gravity affect tides? Aren't the ...
0
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0answers
51 views

Why doesn"t centrifugal force throw us off the earth? [duplicate]

I was drawing a diagram and trying to resolve all the forces. It seems to me that because of gravity, centrifugal force will produce a sort of "dragging" motion along the surface of the earth. The ...
78
votes
8answers
17k 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 ...
3
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2answers
114 views

How do you know which way to choose the limits of an integral?

I am reading http://www.feynmanlectures.caltech.edu/I_13.html#Ch13-S4 In the beginning of equation 13.18, in which Mr. Feynman calculates the potential energy of an object outside a spherical shell, ...