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

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86 views

Why do stellar boundaries exist?

What theorems or insights are available to decide wether a star with some given interdependence between its density, pressure and temperature distributions ought to have a boundary at a finite ...
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2answers
102 views

What general relativity predicts in such a situation?

If there's a system of a point mass or point particle with mass 'm' and a structure such that - The structure is made of many concentric spheres (shells) with certain thickness and the radius of those ...
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0answers
34 views

Calculating Gravity: Small scale vs Large scale

In some calculations I've ran, I've noticed that when the gravitational forces between individual particles are calculated and when the gravitational force between bodies are calculated there tend to ...
2
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1answer
516 views

Tangential and radial acceleration in projectile motion

I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and ...
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2answers
246 views

Is the center of mass in general relativity equal to the center of mass in newtonian gravity?

Consider 2 point masses $A,B$ a distance $d$ away from eachother without velocity or rotation spin. Is the center of mass in general relativity equal to the center of mass in newtonian gravity ? In ...
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0answers
37 views

Gravitational force between rod and mass $m$

Why do we integrate along the whole length while finding the gravitational force between a object of mass ($m$) and a rod of length $L$ and mass $M\,?$ Can't we simply use $F=\frac{GmM}{r^2} \, ?$
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1answer
57 views

Do you say it right? [on hold]

If someone asks you your WEIGHT what would you answer in SI Units. My weight is x 'kilogram' My weight is x 'Newton'. As we know that weight is a force due to local acceleration and still most ...
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3answers
171 views

What physics concepts support the observation of the book and paper falling together?

you place a sheet of paper on a book, it falls with it rather than being separated & slowed by air resistance. What physics concepts support the observation of the book and paper falling together? ...
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3answers
42 views

2 airplanes same size and shap different mass

2 identical balls of different mass dropped from same height reach the ground at the same time due to the acceleration of gravity being constant. If I understand correctly the ball with more mass ...
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2answers
45 views

How can I clarify the difference between free falling and Newton's law?

After I have viewed two experiments the first about Newton's law which involves a brick block and feather letting them fall one time in a vacuumed room they fall at the same time and another time in ...
10
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2answers
641 views

Why does electric force depend on the medium?

Comparing the equations for the gravitational and electric force $$\vec{F}_g=-\frac{Gm_1m_2}{r^2}$$ and $$\vec{F}_e=\frac{Kq_1q_2}{r^2}$$ I noticed the only major difference between them is that ...
0
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0answers
46 views

Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
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2answers
535 views

Tension in string and gravitational force on bob relative strength

When calculating time period of simple pendulum (an approximation of SHM at small amplitudes) we take gravitational force greater than tension in string and resolve gravitational force in two ...
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1answer
43 views

Vector Addition and Gravitational Forces [on hold]

I was given the following question in my Physics class :- Four particles of masses m, 2m, 3m and 4m are kept in sequence at the corners of a square of side a. What will be the magnitude of the ...
0
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1answer
42 views

Path of a swinging object on a rope [closed]

With my lanyard in hand (weighted by my keys), a gentle swinging motion will put the keys in pendulum motion, swinging back and forth. Pendulum motion is relatively easy to model since it is ...
-1
votes
2answers
96 views

What is my real weight? [duplicate]

My weighting machines notes my weight to be 65. Should I read it 65N or 65kg. PS: I only need a correct comment. This question is different, since, I know very clearly what mass and weight are. But ...
3
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2answers
2k views

How gravitation affects tides

I know that tide is caused by the gravitational pull of moon but what I don't know is how it affects water. I have actually these doubts. Why does gravity of the moon creates tides only in water? ...
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2answers
356 views

Kepler's laws to determine radius of circular orbit

"In nonrelativistic limit of general relativity there is a correction to the Newtonian gravitational potential energy $−h/r^3$ with $h = αL^2/(mc)^2$, where $c$ is the speed of light, $α = GMm$ ...
2
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2answers
113 views

Fired a bullet upwards, can it fall down and kill me?

I know that if something is thrown up with a velocity v, it comes down with the same velocity as long as its motion faces no resistance. So is it possible for me to fire a bullet and be killed if it ...
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0answers
42 views

Find Time it Takes For an Object in Free Fall To Hit Ground With Given Gravity [closed]

Sorry if this seems like a simple question. I'm not that good with physics but I'm willing to learn! So my question is, how can I find the time it takes for an object at "h" height to hit the ground ...
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0answers
33 views
11
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1answer
554 views

What are common methods for calculating the time dependency of elliptical orbit?

After playing a game called "Kerbal Space Program" I got interested in orbital mechanics and started messing with simplified calculations to determine $\Delta v$ requirements. In which I compared two ...
2
votes
4answers
328 views

Will this rope break due to the tidal forces or not?

While I was thinking about how tidal forces can make objects float at the surface of a planet orbiting a massive object like a black hole, the fact that any material on the Earth isn't held together ...
3
votes
1answer
106 views

Relation between eccentric and true anomalies

If $v$ is the true anomaly and $E$ the eccentric anomaly, how can I show that $$\frac{dv}{dE}=\frac{b}{r}=\frac{\sin v}{\sin E}~?$$
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1answer
48 views

Optimal time for satellite rocket launch considering moon gravity [closed]

As per this The Gravitational Force of the Earth and Moon on Each Other Moon is pulling us with a force equal to 1/300,000th of our weight. I have read this Is the fuel burn for a satellite launch ...
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3answers
155 views

When does normal force equal to $mg$?

Can someone once and for all explain when does normal force equal to mg? I know for sure that when there is no friction, normal force will be equal to mg. But, i encountered some questions when there ...
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2answers
827 views

How can gravity truly be infinite?

From my knowledge, gravity is infinite and extends throughout all of space. It diminishes as distance increases but is still present everywhere. So given enough time, no matter where something is in ...
3
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1answer
66 views

Do we feel 0.4% less body weight on mount everest?

Weight of the object at surface of earth(where $g=9.8066$). considering Weight=$100~\rm kg$ ,Weight ($W_1$)=$mg$ , mass=$10.1972~\rm kg$ At mount Everest top: Height of Mount Everest = $8.848\rm ...
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3answers
59 views

What influence has the distance of the moon on the height of the tides?

As the Moon recedes from the Earth, are the tides getting taller or shorter? If the Moon is, someday, twice as far from the Earth, how many high tides will be there be each day?
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3answers
454 views

Advantages/Disadvantages of “hanging off” a motorcycle when leaning

The closest question I could find with regards to this subject was this one: Countersteering a motorcycle However, it does not address the specific physics of what I would like to know. There are 3 ...
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2answers
115 views

Does center of mass affect how an object falls?

Suppose you drop an object which has tow ends, of which one is heavy and the other is pretty light. Will the object fall with its heavier end downward or with the lighter one? Why does it happen?
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0answers
23 views

What forces act on a caravan being towed by a car? [closed]

What forces act on a caravan that is being towed by a car? How does this compare to a simple car travelling at a constant speed?
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2answers
217 views

Sun's tidal force on Earth

My question is regarding effect of Sun's gravity on earth. I want to know that if Sun's gravity can change Earth's landscape in long duration (i.e. billion of years) or not? Means if earth is dead ...
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3answers
4k views

Forces on a ball thrown upwards

When a ball is thrown up in upward direction, it is said that force is in downward direction. Why we don't we consider the force given to the ball to throw up in the upward direction? Is there is no ...
3
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0answers
18 views

Shapes of planets? [duplicate]

I was wondering if there was a general explanation as to why it is that all the planets we observe are roughly spherical, and never flat/planar like galaxies. Could there potentially be flat or ...
3
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2answers
47 views

A hollow planet [duplicate]

Consider a planet with the same mass and diameter as Earth, except that it is 1) perfectly spherical. 2) a hollow shell 1 meter thick, so the planet is almost like a massive ping-pong ball. ...
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4answers
108 views

Physics newb: Why can't I plug $E=mc^{2}$ into $W=mg$?

Starting with $E=mc^{2}$, I solved for $m$ and plugged the result into $W=mg$. Which was very confusing, as objects at rest had no weight: $$W = (e/c²)\cdot g \implies W = (0/c²)\cdot g \implies W ...
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1answer
42 views

Couple of questions about Gravitational field of an infinite plane

Is it possible to find the gravitationaal field without using infinite integrals or Gauss's law? I would like to know if so because I haven't learnt doing infinite integrals or using Gauss's law yet. ...
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3answers
109 views

A gravity question [closed]

Does gravity have a unit like length is metres?
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0answers
39 views

Solution to gravitational two-body problem in case of hyperbolic orbits [closed]

Given two bodies and their positions and velocities at a given time $t_0$, as well as their masses, and the knowledge that their relative velocity is high enough that they will not be gravitationally ...
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2answers
38 views

Terminal velocity of mentos [closed]

If somebody throws a mentos downwards (vertically) faster than the terminal velocity of a mentos, from the height at which the terminal velocity is reached from a falling mentos, will the mentos hit ...
0
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2answers
2k views

What is going on in the system? How are the formulas $mg \sin(x)$ and $mg \cos(x)$ derived?

When a load is resting on an inclined plane, there is force $mg \sin(x)$ that's vertical to the inclined plane and force $mg \cos(x)$ horizontal to the plane acting on it like this: My textbook ...
5
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1answer
264 views

Derivation of Universal Variables

Does anyone know of link to the derivation of the Universal Variables? This is in regards to Kepler's equations. The Wikipedia link didn't have enough information for me, and the Colorado page ...
4
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2answers
45 views

Hypothetical binary planet of different size and mass, would they tend to have the same size and mass?

Imagine a binary planet where one of the planet is of the size and mass of Jupiter (planet A) while the other would be like the Earth's moon (planet B). Imagine that this system is extremely stable ...
4
votes
0answers
36 views

Solving for big $G$ in a Cavendish's torsion balance [closed]

I'm having trouble with determining gravity in a Cavendish experiment (torsion balance): I don't really get one question in my textbook regarding this torsion balance. The question asked if one of ...
0
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1answer
266 views

Solving the Three-body problem numerically

I want to create a program in $Mathematica$ that solves numerically the Three-body problem by Euler-Lagrange's equations. I was searching some methods to sucessfully do it. So I found a way to solve ...
1
vote
4answers
3k views

Why doesn't the Gravitational Force causes body to fall towards orbital center moving with constant tangential speed? [duplicate]

Suppose a satellite is orbiting the Earth. The gravitational and centripetal force supposedly point towards the Earth. Therefore, the net force is towards the Earth. Since the satellite doesn't fall ...
3
votes
2answers
79 views

Confusion with $F=-\nabla V$, $F$ conservative

I am rather confused by the relationship $F=-\nabla V$. If a pen drops from a height it loses potential energy so $\nabla V$ is negative. From the above equation this means that the gravitational ...
1
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1answer
98 views

Prove that time for planet to fall into the Sun equals $\left( \frac { 1 }{ 4\sqrt { 2 } } \right)$ of the planet's period [closed]

If a planet was suddenly stopped in its orbit supposed to be circular, show that it would fall onto the sun in a time $\left( \frac { 1 }{ 4\sqrt { 2 } } \right) $ times its time period. I am ...
3
votes
1answer
61 views

Second Kepler's law implies that constant velocity

I was trying deduce that if we suppose that the planet's orbits are circular and de Kepler's secong law is true: A line joining a planet and the Sun sweeps out equal areas during equal intervals of ...