The Newtonian model of gravity in which the force between two objects is given by GMm/r^2.
1
vote
1answer
224 views
Einstein's Explanation for gravity vs. Newtonian
I was trying to understand the Einstein's explanation for gravity (gravitational force), and while I am able to understand why two moving masses will be attracted, due to the curving of the space, I ...
0
votes
1answer
82 views
Newton's Gravitational Law [closed]
Is this correct..?
Gravitational constant, $G = 6.67 × 10^{-11} Nm^2kg^{-2}$
Mass of Sun, $M = 1.99 × 10^{30} kg$
Mass of Earth, $m= 6.02 × 10^{24}kg$
Distance between Sun and Earth, $R= 1.5 × ...
2
votes
2answers
112 views
Force to use in harmonic oscillation through the inside of a planet
I am to find an equation for the time it takes when one falls through a planet to the other side and returns to the starting point. I have seven different sets of values - mass of object falling, mass ...
0
votes
0answers
19 views
Capsule traveling through a planet, find time for return [duplicate]
Possible Duplicate:
If it was possible to dig a hole that went from one side of the earth to the other
A corporation is building attractions in outer space, in which they drill tunnels ...
0
votes
2answers
2k views
Why do objects with different masses fall at the same rate? [duplicate]
Possible Duplicate:
Confused about the role of mass
Today we were in our Literature class talking about the Renaissance and the Enlightement and our teacher also said that scientific ...
46
votes
7answers
3k views
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 ...
3
votes
1answer
609 views
Is acceleration due to gravity constant?
I was taught in school that acceleration due to gravity is constant. But recently, when I checked Physics textbook, I noted that
$$F = \dfrac{G \cdot m_1 \cdot m_2}{r^2} $$
So, as the body falls ...
2
votes
2answers
147 views
Is the gravitational constant G a minimum value in some sense?
Assume a central body of mass $M$, and call $a$ the acceleration of a test
body at a distance $r$ due to any interaction whatsoever with the central
body. Is is correct to say that the ratio $a r^2/ ...
3
votes
2answers
160 views
Gravitational inverse-square law
I was looking at the gravitational inverse-square law:
$$
F_G = G \frac{Mm}{r^2}
$$
This law comes from some experimental data? Why it is an exact inverse-square law? Could it be
$$
F_G = G ...
0
votes
1answer
126 views
Vertical Loop like Anti-gravity
Let's take a bottle (no cap) with half its volume filled with water. If we rotate the bottle at some slower average velocity, water does not drop out of it. The same principle works on Roller ...
0
votes
2answers
776 views
Physics behind Water drops during falling from a tap
what is physics behind Water drops during falling from a tap.
water drop animation
A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces.
Why Water ...
-1
votes
4answers
203 views
How to send a spacecraft to the moon without any acceleration
I have two (maybe equal) question
1- Is this possible to send a spacecraft to the moon without any acceleration(Constant speed)?
2-Is this possible to throw a ball on the top of tree without any ...
3
votes
2answers
648 views
First integral of an equation of motion: $\mu\ddot r=-\frac{k}{r^2}$
I've got an equation of motion (EOM), which is
$
\mu\ddot r=-\frac{k}{r^2}
$
How do I find the first integral of this EOM? I'd appreciate it if someone could show me the steps involved. I should ...
0
votes
1answer
193 views
Time taken for object in space to fall to earth
The Problem
For a small mass a distance $R_i$ away from the center of the Earth, how long would it take for the object to fall to the surface of the Earth, assuming that the only force acting upon the ...
2
votes
1answer
161 views
Would the Moon drift away from the Earth due to extraction of tidal energy? [duplicate]
Possible Duplicate:
Why does the moon drift away from earth?
It seems to me that, due to conservation of energy, the moon would drift away from the Earth if humans began extracting large ...
0
votes
2answers
334 views
Does effective potential for a gravitational force have a maximum below $E=0$?
The relevant figure is below (taken from Goldstein's Classical Mechanics). This figure plots the effective potential for a gravitational force. Does the effective potential $V'$ go flat below $E_2=0$? ...
0
votes
1answer
129 views
why does gravitational force bring the clouds down? [duplicate]
Possible Duplicate:
The Density of Clouds
according to definition of cloud :
A visible mass of condensed water vapor floating in the atmosphere, typically high above the ground
as there's ...
5
votes
3answers
243 views
Negative Mass and gravitation
Since Newtonian gravity is analogous to electrostatics shouldn't there be something called negative mass? Also, a moving charge generates electric field, but why doesn't a moving mass generate some ...
2
votes
1answer
309 views
Formula of Gauss' Law of Gravitation
Gauss's law for Gravitation:
$$\int g\cdot \mathrm{d}S=4\pi GM$$
where $g$ is the gravitational field and $S$ is the surface area.
Am I correct?
2
votes
1answer
164 views
Do Lagrangian points actually maintain a fixed distance?
I was reading on up Lagrangian points and the restricted three-body problem.
From what I was able to tell, the Lagrangian points are 5 points in a two-body system such that a third body would be ...
1
vote
3answers
93 views
How can one know if a theory allow action at a distance effects or not?
1-In general, if a theory has action at a distance effects, where can that appear exactly in the theory?
2-Does it appear in the dynamical law of the theory? (does it appear in Newton's 2nd law? ...
0
votes
2answers
179 views
Hanging a Hammock
I have a hammock that I want to hang using a tree on one end and a wooden post set in a bucket of cement on the other end.
How would I determine how heavy the cement needs to be so that it would ...
0
votes
4answers
544 views
Questions from elevator ride
I like to play inside the lift (elevator). For instance, there are bars attached at the side of the lift, and I like to hold my body up using my two hands on the bar. I realised that I actually feel ...
2
votes
3answers
289 views
Does a toy top weigh less when it is spinning?
I am under the understanding that a toy top will weigh less when it is spinning. The Russians made a spinning type transport back in the 70s to lessen its payload over the tundra. Is this an effective ...
1
vote
5answers
250 views
Electro-gravitation - is it real?
I came across an article claiming that if you charge two plates, one positive and one negative, and fasten them together (assuming they are insulated from each other), they will float in the air. I ...
3
votes
1answer
296 views
Change in appearance of liquid drop due to gravity
A liquid drop is spherical in shape due to surface tension. But why does it appear as a vertical line under the free-fall due to gravity? (E.g. During a rain - falling raindrop) Is there a specified ...
1
vote
2answers
424 views
Free fall of two spheres made of same materials, different masses, with air resistance
Two people falling with the same parachute will gain different speeds if their masses are different. The upward air drag will needed to be bigger for a heavier person, since gravitational force is ...
5
votes
2answers
200 views
Why is there this asymmetry between the two foci of an orbital ellipse?
Why does the Earth revolve with the Sun at one of its foci? Does the other focus do nothing? Why is there this asymmetry in our solar system?
0
votes
1answer
174 views
Gravitational force?
We know that two mass particle attract each other with a force
$$F~=~\frac{G M_1 M_2}{r^2}.$$
But what is the reason behind that? Why does this happen?
3
votes
1answer
492 views
Combining Proportions to get Newton's Law of Universal Gravitation
I've read a little on the history of Newton's Law of Gravitation and noticed that the formula can be separated into 3 distinct parts that lead to the end result of $F_g = G \frac{m_1 m_2}{r^2}$; the ...
2
votes
5answers
977 views
Why Gravity attracts all objects with the same speed?
Why Gravity attracts all objects with the same speed? Is this question was solved? What is the exact answer?
1
vote
1answer
146 views
How do I factor in multiple forces into these Newtonian mechanics equations?
Say a person is walking along.
He then jumps.
The person weighs $25$kg (irrelevant?).
Just after jumping, his velocity is 5m/s (positive is taken as up).
Gravity is taken as ...
2
votes
1answer
136 views
Newton's law of gravitation in complex form
In an ebook about elementary complex analysis I came across Newton's law of universal gravitation with a complex valued function in place of $r(t)$. Can somebody please explain the intuition about how ...
1
vote
2answers
213 views
The two-body problem: What is force between them?
Two bodies with similar/different mass orbiting around a common barycenter.
What is force between them, where $F_{12}$ is the force on mass 1 due to its interactions with mass 2 and $F_{21}$ is the ...
4
votes
4answers
419 views
what is the 2D gravity potential?
In 3D, I can calculate the total force due to gravity acting on a point on the surface of the unit sphere of constant density, where I choose units so that all physical constants (as well as the ...
1
vote
1answer
96 views
Gravitation and equilibrium (…and similar problems)
One problem that I'm having trouble with (as opposed to the other):
The Messenger is a probe that orbits Mercury $700 \rm km$ from the surface. What is the tangential velocity it should be ...
0
votes
0answers
68 views
Trajectory of a photon due to a constant/uniform gravitational force [closed]
I have a small problem of physics linked to a basic ray tracing algorithm. My problem is the following :
At $t = 0$, a photon at the position $(x_0 = x_\text{min},y_0 = y_\text{min})$ with the ...
3
votes
2answers
217 views
At what g is terminal velocity not terminal?
How weak would gravity need to be in order for a human to reliably survive the terminal velocity of falling through air?
(Context: watching scifi on a space station with a variety of artificial ...
2
votes
2answers
496 views
Why is the center-of-mass of 2 bodies at the focus of their elliptical orbits?
Why is the center-of-mass of 2 bodies (which interact only via Newtonian gravity) located at a focus of each of the elliptical orbits?
I know that when there are no external forces, the center of ...
4
votes
2answers
238 views
How much thrust would be needed to turn a hobbyist weather balloon into a deep space probe?
I was reading the article Weather Balloon Space Probes that says you can put your own balloon probe at 65,000 ft temporarily.
Is it even remotely possible to raise the probe high enough using ...
3
votes
5answers
363 views
Does Newtonian mechanics predict the bending of the course of light by objects with mass?
$F=Gm_1m_2/d^2$
$F=ma$
$a_g=Gm_{other}/d^2$
In Newtonian mechanics, the acceleration of object A toward object B is not dependent on the mass of object A but on the mass of object B and the ...
1
vote
1answer
71 views
What's the amount of deviation of cellestial orbits from perfect ellipses
It's well known that the planets don't orbit the sun in perfect circles and the characteristics of the elliptical orbits which serve as better approximations to their motion have been calculated ...
19
votes
1answer
710 views
Why does it take so long to get to the ISS?
I don't understand why when first launched Space X's Dragon capsule had to orbit the Earth many times in order to match up with the ISS? Was this purely to match it's speed, or to get closer (as in ...
0
votes
2answers
99 views
Calculating kinetic energy?
Would this be a valid equation to calculate kinetic energy created from a drop from a height:
$$E_{kinetic} ~=~ v_{vertical}tmg$$
Velocity multiplied by time gives distance. Distance multiplied by ...
2
votes
1answer
147 views
Does a slinky hanging downward double in length if gravity doubles?
Also would a spring under tension greater than the force of gravity pulling the spring downward shrink in both directions until it has depleted it's stored energy while in free fall?
5
votes
1answer
318 views
Kepler problem in time: how do two gravitationally attracting particles move?
Two particles with initial positions and velocities $r_1,v_1$ and $r_2,v_2$ are interacting by the inverse square law (with G=1), so that
$$ {d^2r_1\over dt^2} = - { m_2(r_1-r_2)\over |r_1-r_2|^3} $$
...
0
votes
2answers
272 views
When we throw an object in the presence of gravitational attraction is the mass of the object proportional to the time of fall or not?
I was confused when i saw two object of different masses (A and B)falling from the same height(h) but both of them strikes the ground at same time. Is this possible, that masses of the objects are ...
2
votes
1answer
75 views
How should I be thinking about tides?
I am working on a project for physics that involves tides. This is my current mind set when thinking about tides:
The earth applies a gravitational force on some mass ...
0
votes
1answer
344 views
How calculate the angle to launch an object at the maximum distance?
Suppose that you want to launch an object that travels the longest distance, given the starting speed (or the force applied). You have to determine the angle that al you to reach the longest distance, ...
9
votes
1answer
274 views
Apollo and orbital mechanics: orbital decay if the Trans Earth Injection (TEI) burn had failed
I'm reading Jim Lovell (Apollo 8 and 13) and Jeffrey Kluger's book Apollo 13, which is a fantastic read about a long past era I only have kindergarten memories of. On page 54 there is a paragraph that ...
