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

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Why does acceleration seem not to be the gradient of gravitational potential?

Consider a spherically symmetric distribution of density $\rho(r)$. We can define the mass enclosed within each radius $r$ using $\frac{dM(r)}{dr} = 4\pi r^2 \rho(r)$, with the condition that $M(r=0) ...
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3answers
615 views

Gravitational doubt [duplicate]

If we can shield a charge from electrical forces by putting it inside a hollow conductor. Can we shield a body from gravitational influence of nearby matter by putting it inside a hollow sphere or by ...
0
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1answer
56 views

Balancing stick on hand - inverted pendulum motion

How do I calculate the velocity and acceleration of a stick that is vertically on my hand? How fast and far do I need to move my hand from side to side to keep balancing the stick? Assuming that we ...
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1answer
52 views

How to find the force of the compression at the core of a planet?

For example the core of the planet Jupiter, how to find out the magnitude of the force that compresses its core? and can that be thought of as the total force that holds the planet together?
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1answer
59 views

In a universe that is expanding at a constant rate, do objects that are attracted to each other feel a force opposite to their attraction?

In this article, the authors make the claim (pg 44) that "Expansion by itself—that is, a coasting expansion neither accelerating nor decelerating—produces no force." I'm having a hard time convincing ...
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4answers
588 views

Why are people weightless whilst in orbit around the Earth? ISS? Satellites? [duplicate]

Had physics for 2 years now on highschool, but there is a thing I am wondering about. You know the in the height above the earth surface around where the satellites are (Or the ISS), I've calculated ...
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1answer
48 views

Two equations for $y$ in projectile motions

I have two equations on my equation sheet: $$y=v_o t \sin \theta - \frac{1}{2} g t^2.$$ And then another: $$y_{\max} = \frac{v_o^2 \sin 2 \theta }{2g}.$$ I understand that the first one is an ...
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2answers
241 views

Why do we orbit around the sun instead of one the other stars?

I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling. What is so specific about our sun ...
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1answer
88 views

Could an orbiting mass generate power?

If an heavy object (e.g. 10 tons) orbiting around Earth at 370 miles high, is connected with a cable back to Earth, we assumed either Earth is going to pull the mass or vice versa (or it will fall ...
0
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1answer
52 views

It is a numerical [closed]

If the densities of the moon and the earth are related by $\rho_m / \rho_e =3/5$, and if $g_m /g_e = 1/6$, then what is $R_m /R_e$? ($g=$ acceleration due to gravity and $R=$ Radius)
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1answer
103 views

Calculate analytically the time until two spheres meet due to gravitation [duplicate]

Imagine you have two homogeneous spheres with the same diameter of $d=0.1 m$. They have the same mass $m = 1 kg$. The distance between the centers of mass is $r= 1 m$. Their electrical charge shall be ...
2
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0answers
81 views

Force of gravity in the event horizon [closed]

I recently posted a question about black holes and gravity (this) and I discovered the Schwarzschild radius: $r_s=\frac{2GM}{c^2}$. I thought with a friend of mine about the actual force (in Newtons) ...
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2answers
46 views

Velocity required for orbit of satellite

I am very confused about orbital velocity for satellite launched from earth. It is states that: $$ v=\sqrt{\frac{GM}{r}} $$ Some says that it is equal to 8000 m/s and some say 3.1 km/s. Please remove ...
4
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3answers
86 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 ...
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3answers
86 views

Would an Object Near a Pre-Blackhole Star Experience the Same Gravity as Post-Blackhole?

My question was inspired by this question, which got me thinking. According to Newton's Law of Gravitation, $$F = G\frac{m_1m_2}{r^2},$$ the gravity of an object is inversely proportional to the ...
5
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2answers
348 views

Does the mass of a star change as it collapses into a black hole?

I know (I think!) that when a really big star collapses on itself it creates a black hole. My question: When a star collapses, is the mass equal to the mass of the star when it's not a black hole? Or ...
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3answers
251 views

Gravity force between two objects with different mass

We know thanks to Newton that: $$F=G\frac{m_1\cdot m_2}{r^2}$$ Where $G$ is the Gravitational Constant that is about $6.673\cdot10^{-11}$ $m_1$ and $m_2$ are the masses of two different objects ...
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2answers
342 views

Loop-the-loop question [closed]

Problem: The marble rolls down the track and around a loop-the-loop of radius R. The marble has mass $m$ and radius $r$. What minimum height $h$ must the track have for the marble to make it around ...
4
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3answers
172 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
33 views

Gravitional force

Does the gravitation of Earth have a limit? when a body projected vertically with $v=11km/s$ (escape velocity) from Earth's surface does this means that it does not return back to Earth?
3
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3answers
133 views

Why aren't there more natural satellites orbiting the Earth than just the Moon?

Considering that there's a lot of debris in space and that impacts fling out rocks into space all the time, why do we only have one large natural satellite - the Moon? Shouldn't there be all kinds of ...
2
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1answer
74 views

A zero gravitational potential and non zero gravitational field

Give an example of a situation in which there is a non-zero gravitational field and a zero gravitational potential at the same point? $$dV=-\vec E\cdot d\vec r.$$ The above equation implies that ...
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0answers
36 views

Dependence of Force as a function of Distance? [duplicate]

Why is the strength of a field (i.e. gravitational or electric) inversely correlated to the square of the radius? It is clear to me why the further you get a way from a field, the field's enacted ...
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4answers
121 views

Gravity and acceleration

I've imagined this little scenario to help me conceptualize things. Let's say we have a doughnut-shaped object with a hole whose diameter is greater than that of a sphere. Let's say that the sphere ...
0
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1answer
59 views

Calculating Gravitational Attraction Involving Massless Objects

Using the formula $F=G\frac{m_1m_2}{d^2}$ where $m_1$and $m_2$ are the masses of two objects, $G$ is the gravitational constant, and $d$ is the distance between the objects, it is possible to ...
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2answers
118 views

Potential and kinetic energy on spherical surface

A small particle of mass $m$ is atop of a semi-sphere as shown in the figure. A little push was given to the particle. Prove that the particle will leave the spherical surface at a height of ...
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3answers
90 views

Electrostatic and gravitational forces? [closed]

Electrostatic force between two charged particles depends on the magnitude of the charges and the distance between them. If the charges have mass $m$ and $m'$ then, what will be the total force ...
2
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3answers
338 views

Why do objects fall at the same acceleration?

I read these two posts and now I am more confused. Do heavier objects fall faster? Don't heavier objects actually fall faster because they exert their own gravity? I was going to ask: if mass ...
0
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1answer
95 views

Gravitation - why is it so confusing?

First, does gravity emit from all directions around a star or planet equally. Secondly, how is it that gravity pulls a planet closer, then it goes further out, without the planet changing orbit ...
1
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1answer
81 views

What are Lagrange points in gravitation fields? [closed]

What are Lagrange points in gravitation fields? Additionally, what are their properties? For example, if a satellite or asteroid rested at a Lagrange-point.
0
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6answers
226 views

Is gravitational force affected by intervening medium?

If we leave a iron ball and feather into the water, feather returns to the surface and floats or moves into the water slowly. On the other hand, iron ball (of certain mass greater than mass of ...
0
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3answers
185 views

Pendulum (highschool)

I have a question concerning pendulum. On our physics lessons we built simple pendulum consisting of weight and a thread ($\ell=0.31$ m). We tried to calculate $g$ from the well known formula $$T_m ...
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1answer
72 views

Is a scaled-up aircraft carrier 'ski-ramp' a viable system to impart enough velocity to significantly assist a spacecraft to orbit? [duplicate]

Not a boost straight up to escape velocity, just sufficient added momentum to make a significant economic saving on fuel cost, mass and complexity of a standard launch. It seems ludicrous to me how ...
5
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3answers
337 views

Home experiment question

I want to make a home experiment where I roughly explain the phenomenon of water remaining in a straw if you close one end of the straw. So I'm thinking that the weight of the water is pulling it ...
18
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3answers
2k views

How is gravity consistent when you split an object into multiple pieces?

Here's the picture: In picture 1: Assume that we have 2 objects, namely A, and B. Object A with mass $2M$, and object B with mass $m$; and their distance is $r$. Then the gravitational force of A ...
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0answers
77 views

Finding gravitational potential due to ring [closed]

A point P lies on the axis of a fixed ring of mass M and radius R at a distance of 2R from its centre O. A small particle starts from P and reaches O under gravitational attraction only.its speed at O ...
0
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1answer
63 views

Integrating for speed [closed]

Trying to determine the speed of a falling body with respect to traveled distance and initial speed. I've been provided with the following equation for acceleration as a function of distance and the ...
0
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0answers
29 views

What will change if we have another Earth in the space near Earth? [duplicate]

If a new Earth came and orbit our Earth within 300,000 km to Earth? I just did not know. thanks.
0
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0answers
59 views

Free fall from space [duplicate]

If you leave a ball weighing 10 kg at a height of 500 km above sea level (neglecting air friction). How can calculate how long the ball hits the ground and what will be its speed? I know that: On ...
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2answers
124 views

Can effect of gravity be broken (counteracted) by electric force?

Can we make a jacket using an electronic circuit that uses electric force to cancel the effect of gravity so that we get lifted in air.
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0answers
36 views

Choosing proper centripedal force in Newtonian gravitational forces [closed]

I am trying to do an orbit simulation, I took Newton's law of Newtonian gravitational forces. It seems to work correct, but I can't really determine the velocity of an object needed to stay in free ...
1
vote
1answer
150 views

Free fall time with non uniform acceleration and some initial velocity

Free-fall time for two objects on a radial path (starting from rest) is given by: $t(y)=\sqrt\frac{y_0^3}{2u}\biggl(\sqrt{\frac{y} {y_0} \bigl({1} -\frac{y}{y_0}}\bigr) + ...
-1
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1answer
196 views

free falling object with air resistance?

we already know that if we plot speed vs time of free falling object it will be y=gx graph because we know the acceleration is gravity. If it have air-resistance acceleration will be change right?. ...
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1answer
86 views

Newton's Law of Universal Gravitation for extended objects

Carroll and Ostlie write, in their book An Introduction to Modern Astrophysics (second edition), at the page 33, right after deriving Newton's Law of Universal Gravitation for two point masses using ...
-1
votes
1answer
118 views

Calculating pitch and roll with accelerations greater than +/- 1g

I'm looking to compute the pitch and roll of a device fitted with a three axis accelerometer when it is not at rest or moving at a constant velocity. Most applications I've seen so far are for ...
0
votes
2answers
81 views

A small object on the opposite side of the earth's orbit with 0 velocity,“in line” with the core - would it collide with the earth?

If a small object (say mass 1 kg), at the opposite side of the earth's orbit (six months away), was placed in the same orbital position as the earth's core, at zero velocity in all directions, would ...
2
votes
2answers
204 views

Why do the planets orbit the Sun? [duplicate]

Why do the planets orbit the Sun? If it's because the gravity of Sun then why don't they just fall in and burn up?
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4answers
175 views

Can you lift yourself standing on a wooden block using pulley mounted on block? [duplicate]

I am new to this site. Please help me figure out this problem. Is it possible to lift oneself like shown in schematic? Waiting for good suggestions. Chirag
1
vote
1answer
101 views

Is speed squared constant?

q. A heavy particle is projected at speed $U$ at an angle $\alpha$ to the horizontal. The particle is subject to air resistance which is experimentally found to vary proportionally to the square ...
1
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1answer
248 views

3D ballistic trajectory with quadratic drag. Calculating position and velocity at time $t$

A particle starts at the origin and has an initial velocity represented by a 3D vector. The particle experiences gravity and air resistance with quadratic drag (based on velocity^2). What I've been ...