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

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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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2answers
303 views

Why are heavy things harder to lift?

According to multiple websites, any object in free-fall (no air resistance) on earth will accelerate towards the Earth at 9.8 m/s. If all objects fall towards the Earth at the same rate, regardless of ...
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1answer
87 views

How can we prove simply that acceleration for every freely falling body is equal to $g$? [duplicate]

If I allow two bodies of different masses to fall freely from same height towards the earth, how can I prove that the acceleration produced in both was constant and equal to gravity.
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Will an object falling into Earth's orbit start spinning?

Assume an object falls towards Earth (I've drawn a hyperbolic orbit, but this would apply to any orbit). The object starts at $A$, and at this point it is not rotating i.e. an observer on the object ...
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1answer
52 views

Do all thing move against gravity with -9.8 meter per second squared acceleration?

If I throw a ball to height h above the earth's surface and then shoot a bullet that reaches the same height but would there be same quantity of acceleration produced in both?
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2answers
104 views

What is the meaning of the negative sign in $W = -\Delta U$?

What is the meaning of the negative sign in $W = -\Delta U$ ? As far as I understand, $W = -\Delta U = -(U_f - U_i) = U_i - U_f$. While $U_i$ is the initial potential energy (before applying the ...
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48 views

Differential Equations for Two-Dimensional N-Body Simulation

So I recently asked a question about improving the stability of a two-dimensional orbital simulation (as before I was using Euler integration). I was told to use Runge-Kutta 4 for a more stable ...
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0answers
87 views

How much time would it take for a free-falling ghost-like object to cross the entire Earth? [duplicate]

We have an object of mass $m$ which can go through matter like a ghost. It's only affected by gravity, not by any other force, so it's in free fall. At the instant $t=0$ it is at the surface of the ...
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If the gravity at the center of the Earth is zero, why are heavy elements like iron there?

If gravity is zero at the center of the earth, why is there a core of heavy elements, such as iron? Alternate question for the opposite hypothesis: If gravity is greatest at the center of the ...
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2answers
78 views

Air Drag in orbit

Artificial satellites don't orbit the earth forever. Eventually the Earth's atmosphere, thin as it may be up there, will bring them down. But did you know the linear speed of a satellite in a near ...
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24 views

weightlessness and forces conceptional question

I am currently learning about forces and newton's laws of motion. I have a question in my book which I don't understand though... Here it is: (note: I dont want the answer I just want to understand ...
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1answer
95 views

Motion in the gravitational field along a trajectory [closed]

A point particle of mass $m$ is moving in the gravitational field along some trajectory which is described by the function $y=y(x)$, which is in a vertical plane and is continuous. Initial ...
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1answer
78 views

Two body problem with given start positions and velocities [duplicate]

I am trying to program a $n$-body problem simulation. To calculate the position and velocity after a time-step I want to split it in multiple 2 body problems. Now I am stuck, trying to find the ...
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1answer
33 views

Coexistence at Lagrange points

I was wondering how precise the location of an object in a Lagrange point needs to be to maintain stability, since it seems that several natural objects (asteroids) exists together in some of these ...
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1answer
125 views

Prove that orbits are conic sections

How does one prove that an orbit of a satellite around a planet of significantly greater mass than the satellite is a conic section (i.e. an ellipse, circle, hyperbola, or parabola)? Also, there is ...
0
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1answer
53 views

Minimum Distance for “Speed of Light Approach”

I tried to calculate the minimum distance between a planet and a test mass for the mass to attain the speed of light on colliding with the planet's surface if it were released from rest at the initial ...
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1answer
417 views

Pressure and Tall Buildings

Does living in tall buildings somehow exert more pressure on our bodies? I remember reading something about this once but I'm not sure if its true.
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1answer
83 views

Calculating a two-dimensional orbital path with infinite granularity (non-Euler integration)

For a game I am making, I am trying to calculate the position of an orbiting object around one or more bodies. I have successfully implemented this gravity simulation by calculating the force, then ...
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1answer
125 views

For $N$ particles acting under gravity, how long until they settle into a virial equilibrium?

As the title says, if I have a system of particles interacting only due to gravity, over what timescale do we expect them to fall into a virial equilibrium? By virial equilibrium I mean a system that ...
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4answers
175 views

How do I correctly introduce time into this equation?

So, for the past few years it's been my goal to create an equation that would give me the position of an object in a gravitational field at time $t$, given it's initial position and velocity. At first ...
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2answers
266 views

Infinity problem: Why is gravity $g=0$ zero at the center of Earth if according to Newton gravity formula $g=GM/R^2$? [duplicate]

It is said that value of $g=0$ at the centre of the Earth. $g$ is calculated using the formula $$ g=G*M/R^2.$$ When $R = 0$, $g$ approaches infinity. I have two ...
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2answers
105 views

Intuitive understanding of Lagrange point L3

I learned about Lagrange points today and the physics behind L1, L2, L4 and L5 make intuitive sense to me. But I'm stumped by L3. Wikipedia says "L3 in the Sun–Earth system exists on the opposite ...
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The stability of falling through a planet [duplicate]

Let's say that you were standing on Earth, and stepped into a hole that went perfectly straight down through the entire planet to the other side. Would the terminal velocity of your fall, and the ...
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2answers
133 views

Units in gravitational $N$ body simulations

I am trying to write a code in Python to simulate $N$ bodies interacting through gravity. In particular I am trying to see whether a system of particles with random initial positions and zero velocity ...
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2answers
208 views

Is the method of images applicable to gravity?

It is well known that the method of images is a useful tool for solving electrostatics problems. I was wondering why this technique is not applied when considering newtonian gravity? Obviously there ...
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4answers
173 views

What starts the conversion between GPE and KE?

When researching GPE and KE conversion, lots of websites say that as an object with GPE (Gravitational Potential Energy) falls, that GPE is converted into KE (Kinetic Energy), so there is less GPE and ...
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3answers
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Is it correct to say that falling object are standing still?

As I was browsing youtube I came across the BBC video "Brian Cox visits the world's biggest vacuum chamber - Human Universe: Episode 4 Preview - BBC Two" He drops a bowling ball and a feather in a ...
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5answers
227 views

How gently could a comet/asteroid/meteorite “hit” Earth?

Could an object from outer-space with the right velocity and orbit come into contact with the surface of our planet in a manner that wouldn't cause it to burn in our atmosphere?
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53 views

Why is the gravitational potential energy of ideal uniform massive spring $mgx/2$, not $mgx$?

In this Wikipedia page, $$L= T-V = \frac{1}{2}\frac{m}{3}\dot{x}^2 + \frac{1}{2}M \dot{x}^2 - \frac{1}{2} k x^2 - \frac{m g x}{2} - M g x$$ where $mgx/2$ refers to gravitational potential energy of ...
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2answers
54 views

What is the shape of a gravitation field for a square or cubed mass (say, size of a planet)?

most gravitation models assume a round object as most large masses in space (planets) are more or less round. It is simple to envision that it gravitation pull is also [nicely spherical and diminishes ...
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2answers
89 views

Integrate the law of universal gravitation to get position [closed]

I'm trying to write Physics simulation software which simulates gravitational and electric forces between $n$ bodies. I know how constant acceleration is integrated to get distance, but I have no ...
3
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1answer
119 views

What is the force required to move a raindrop?

I'm doing some research on how much force is required to move a typical raindrop (assuming that it is falling straight down) off to the side of X distance. This is for a school project on creating our ...
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2answers
98 views

How does gravitational potential energy increase, if field decreases as $h$ increases?

(In the following constants are ommitted) Let $ M = 50, m = 5, h = 5$. Then $$ \text{Potential Energy} = \frac{50\cdot5}{5} = 50.$$ While after increasing the height $h$: $ M = 50 , m =5, h =10 ...
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1answer
146 views

Thought Experiment: An object falling indefinitely under gravity?

So the other day, I devised this thought experiment: Consider an infinite tunnel, and you drop a coin of mass $m$ into it. Considering the effect of gravity to be applicable and neglecting air ...
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2answers
68 views

Gravitational Force units

In the formula $F=mg$, does the mass $m$ needs to be in $kg$? And what is exact value of $g$? I've tried with both and didn't worked.
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137 views

Why do planets not stop revolving around the Sun? [duplicate]

Why do planets revolving around the Sun not stop revolving? Note I am not asking why planets do not collapse with Sun.
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2answers
122 views

What would be the photon's effective mass in Newton's Law of Gravitation?

If we equalize the force from the Newton's Law of Gravitation to Force on a photon in a gravitional field (I don't know if there is an equation for it). What would be the photon's effective mass? (I ...
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5answers
515 views

If you are on Earth, are your mass and weight the same?

I was wondering how mass and weight are different so I Googled it. I found that mass is constant no matter where you are because it is the amount of matter in an object and weight changes because it's ...
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6answers
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Throwing an object around the Earth. Is it possible?

Some of you might be familiar with the cartoon called Astérix. In one of the episodes, Obelix (the really strong fat guy in the stylish striped pants) enters a spear throwing competition. He beats the ...
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Traveling to Mars in 24 Days

I am trying to calculate an electromagnetic rail launch from the Moon but I need to know if humans can survive the launch. Please see the specs below. 150 miles of track Proposed final launch speed ...
13
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2answers
764 views

What is a reasonably accurate but simple model of the Milky Way's gravitational field?

I am putting together a toy program which shows how stars move around in the galaxy. To run the simulation I need to know strength of the Milky Way's gravitational field at any location in it. I'm ...
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0answers
35 views

Why is there a difference when we measure the change of gravitational acceleration? [duplicate]

When we go up from the surface of the earth to measure the change of $g$, we use only height. But when we go down from the surface of the Earth, we use the density equation of the Earth. Why?
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0answers
182 views

How the Moon causes the tides?

I am considering the following question but I con't quite figure it out... I have looked up differential gravity but I cannot derive the equation for the effect on earth, and I haven't found any ...
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2answers
87 views

Linear Gravity Inside Solid Sphere Derivation

I am currently taking a dynamics module at university and am revising for a midterm exam. One of the problems on a past paper was to consider a mass falling through a hole in the Earth (pole to ...
0
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1answer
158 views

Clearing up confusion about orbital mechanics

When I see an orbital mechanics problem, I recall the following things from my "toolbox": Angular momentum is conserved for a body orbiting a planet, since the torque due to gravity is 0. Kinetic ...
0
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1answer
131 views

Can we make a “Gravity Mill” based on principle(s) of Newton's cradle?

DISCLAIMER: Newbie/Wannabe Physicist. What's to stop us from making a "Gravity Mill" which is a bar/rod attached with weights on both ends and pivoted at the ...
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1answer
87 views

newton's cradle with 2 balls dropped from same height at same time

I'm creating a logo and want it to be as exact as possible. The logo idea is a "Newtonian cradle", but with only 2 balls and on straight steel wire (can't be bend). What would happen if I dropped ...
6
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5answers
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Evidence that stationary masses in space actually attract each other

I'm finding it rather difficult to find experimental evidence that two stationary masses in space (unaffected by external massive bodies or gravities) actually attract one another. For moving masses, ...
13
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1answer
223 views

Are “echo” explosions near Earth realistic?

Watch the simulation below for better visualization. Suppose we create an explosion, for example at $2R_{Earth}$ from the center of Earth. Just before the explosion was set off, the explosive was at ...
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2answers
94 views

Why does General Relativity predict more light deflection than Netwonian Physics?

If one looks at the limit as light's mass approaches zero, Newtonian Physics predicts a deflection of light (this can be seen by the fact that all objects are accelerate the same due to gravity.) ...