Questions tagged [newtonian-gravity]

This tag is for questions regarding the Newtonian model of gravity in which the force between two objects is given by $~GMm/r^2~.$ It is a natural phenomenon by which all things with mass or energy – including planets, stars, galaxies, and even light – attract one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

The Newtonian model of gravity in which the force $(F)$ between two objects of mass $M$ and $m$ situated at a distance $r$ is given by $F=\frac{GMm}{r^2}$, where $G$ is the Gravitational constant and its value is $G=6.674×10^{−11}$ m$^3$⋅kg$^{−1}$⋅s$^{−2}$ (in SI units).
Newtonian concepts also include the gravitational field, the gravitational potential energy, and the gravitational potential.

It is to be noted that gravity has an infinite range, although its effects become weaker as objects get further away.

The gravitational field is the gravitational force divided by mass. The gravitational potential energy is the integral of the gravitational force. The gravitational potential is given by the gravitational potential energy divided by the mass.

Newtonian gravity can also be formulated in terms of Poisson's equation $\nabla^2\Phi=4\pi G\rho$.

5208 questions
275
votes
11 answers

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 in half—the halves clearly don't fall more slowly…
ErikE
  • 2,996
270
votes
8 answers

Does Earth really have two high-tide bulges on opposite sides?

The bit that makes sense – tidal forces My physics teacher explained that most tidal effect is caused by the Moon rotating around the Earth, and some also by the Sun. They said that in the Earth - Moon system, the bodies are in free-fall about each…
123
votes
10 answers

How can I stand on the ground? EM or/and Pauli?

There is this famous example about the order difference between gravitational force and EM force. All the gravitational force of Earth is just countered by the electromagnetic force between the electrons on the surface of my feet and the ground. But…
115
votes
6 answers

Could we send a man safely to the Moon in a rocket without knowledge of general relativity?

I'm wondering if it's possible to send a man to the Moon using equations consistent with Newtonian gravity and without the elaborate tools of Einstein gravity. Are the predictions made by Newtonian gravity sufficiently precise to plan a successful…
96
votes
4 answers

If Earth had rings?

If Earth had rings, would they center on the equator like Saturn's rings do on its equator?
95
votes
8 answers

Does juggling balls reduce the total weight of the juggler and balls?

A friend offered me a brain teaser to which the solution involves a $195$ pound man juggling two $3$-pound balls to traverse a bridge having a maximum capacity of only $200$ pounds. He explained that since the man only ever holds one $3$-pound…
adamdport
  • 1,157
95
votes
5 answers

Does a gun exert enough gravity on the bullet it fired to stop it?

My question is set in the following situation: You have a completely empty universe without boundaries. In this universe is a single gun which holds one bullet. The gun fires the bullet and the recoil sends both flying in opposite directions.…
94
votes
7 answers

If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, strong nuclear force, and electromagnetism. Those are…
91
votes
9 answers

Why doesn't the Moon fall onto the Earth?

Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
90
votes
3 answers

Why do phones land face down?

Layman here. I'm not sure if this is the case or not, but my anecdotal evidence is that mobile phones, especially large screen phones, tend to fall face down when you drop them; much to the owner's dismay, this leads to cracked screens. I'm sure…
88
votes
8 answers

Could a "living planet" alter its own trajectory only by changing its shape?

In Stanislaw Lem's novel Solaris the planet is able to correct its own trajectory by some unspecified means. Assuming its momentum and angular momentum is conserved (it doesn't eject or absorb any mass), would this be possible (in Newtonian…
Petr
  • 3,119
86
votes
7 answers

Why is the Earth so fat?

I made a naive calculation of the height of Earth's equatorial bulge and found that it should be about 10km. The true height is about 20km. My question is: why is there this discrepancy? The calculation I did was to imagine placing a ball down on…
84
votes
4 answers

Where does the extra kinetic energy come from in a gravitational slingshot?

I read in this answer in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the height it dropped from. In this way, it was said,…
82
votes
8 answers

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?
78
votes
2 answers

Can an atom orbit the Sun?

Is it possible for a molecule or atom to orbit a star (e.g. the Sun)? Or is there always too much outward force imparted by solar radiation compared to the inward force of gravitational attraction?
1
2 3
99 100