The Newtonian model of gravity in which the force between two objects is given by GMm/r^2.
3
votes
1answer
36 views
Why doesn't this equation for orbital motion change with position in the orbit?
The question and answer are on pg.8-10 of this PDF:
At first, I went through it, thinking nothing of it. But then, I wondered: "What if we picked a final state in which the space junk was NOT at ...
11
votes
2answers
187 views
How large can planets or moons appear?
In many artistic impressions or movies there are pictures or scenes where the sky is filled with an enormous moon (as seen from a planet) or vice versa.
I wonder if there is an upper limit to the ...
2
votes
1answer
52 views
Acceleration due to gravity?
I was looking into orbitals and found something I haven't been able to understand.
http://www.math.ubc.ca/~cass/courses/m309-01a/hunter/satelliteOrbits.html
There is a part on the page which states ...
3
votes
2answers
49 views
Why are some jenga pieces easier to remove than others?
Jenga is a game place with wooden blocks stacked on top of one another in an alternating pattern. Players take turns removing blocks from any layer and placing them on top.
As the game progresses ...
0
votes
1answer
67 views
Vector cross product of $\mathbf{r}$ and $\ddot{\mathbf{r}}$ in polar coordinates
I'm struggling with the following question:
Question 6 A planet of mass $m$ moves under the gravitational attraction of a central star of mass $M$. The equation of motion of the planet is
...
1
vote
4answers
126 views
Is it possible to whirl a point mass (attacted to a string) around in a horizontal circular motion *above* my hand?
I'm studying circular motion and centripetal force in college currently and there is a very simple question but confuses me (our teacher doesn't know how to explain either :/), so I hope we can sort ...
2
votes
4answers
101 views
Potential energy sign conventions
Almost every book on physics that I read have some weird and non-clear explanations regarding the potential energy. Ok, I do understand that if we integrate a force over some path, we'll get a ...
2
votes
1answer
32 views
Falling through the ground [duplicate]
I do not know much about physics but I know that according to Newtons third law of motion when we walk we are pushing the ground down but the ground is pushing us up. What force is making the ground ...
5
votes
1answer
149 views
How reliant is the Solar System on being exactly the way it is?
We know that all objects with mass exert forces on all other objects of mass such that
$$ F = \frac{GMm}{R^2}.$$
And as others have discussed the planets do interfere with each other ...
1
vote
1answer
53 views
Defining the star as the ellipse focus rather than the barycenter, what does the other focus do? [duplicate]
There are a lot of images and animations on the internet depicting two bodies orbiting around their common barycenter. The barycenter is defined as the (let's say right) focus of the ellipse.
If we ...
-8
votes
0answers
42 views
not all items fall at the same rate some items have outside facters gain speed in which they “fall” [closed]
I was reading one of the post this morning and found it fasanating with all the formulas that were being poured out about items will falling at the same rate given the same hight that they were droped ...
0
votes
2answers
60 views
Why is potential energy negative when orbiting in a gravitational field?
I had to do a problem, and part of it was to find the mechanical energy of satellite orbiting around mars, and I had all of the information I needed. I thought the total mechanical energy would be the ...
0
votes
2answers
55 views
Constant of gravity in earth fixed coordinate system
I have this problem:
If the constant of gravity is measured to be $g_0$ in an earth fixed
coordinate system, what is the difference $g-g_0$ where $g$ is the
real constant of gravity as ...
6
votes
4answers
124 views
Integrating radial free fall in Newtonian gravity
I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving ...
1
vote
1answer
76 views
Pendulum in an elevator
Suppose we have a pendulum tied to the ceiling of an elevator which is at rest. The pendulum is oscillating with a time period $T$, and it has an angular amplitude, say $\beta$. Now at some time ...
0
votes
2answers
49 views
Escape velocity to intersection of two gravitational fields
Find the minimal velocity needed for a meteorite of mass $m$ to get to
earth from the moon. Hint: the distance between the center of earth
and the center of moon is $\approx 60 R_E$, and the ...
1
vote
1answer
77 views
Gravitational potential energy of mass between two planets
Suppose I want to launch a rocket from earth to some point $O$ between the center of earth and the center of moon (on a straight line connecting their centers), where the gravitational force of the ...
3
votes
1answer
61 views
Tension of rope in the gravitational field of earth
Two balls of mass $m$ each one are connected with mass-less rope with
the same length as the radius of earth. The system is in free fall.
Prove that the tension of the rope when the nearest (to ...
3
votes
2answers
65 views
Orbits within a $-\vec{r}$ field
Let's say that we have a cold dark matter theory, so we imagine weakly interacting particles. Now, let's say that one of those dark-matter particles has a rare interaction while traveling through the ...
1
vote
2answers
79 views
The potential and the intensity of the gravitational field in the axis of a circular plate
Calculate the potential and the intensity of the gravitational field at a distance $x> 0$ in the axis of thin homogeneous circular plate of radius $a$ and mass $M$.
Could anybody describe how to ...
0
votes
0answers
28 views
Understanding Kepler's $2^{nd}$ law in terms of angular momentum conservation
A) Explain how Kepler's $2^{nd}$ law - "The radius vector from the Sun to a planet sweeps out equal areas in equal time intervals" - can be understood in terms of angular momentum conservation.
I ...
0
votes
1answer
66 views
Change in speed of a satellite
Suppose there's some satellite orbiting the earth in circular motion. Suppose there's an asteroid that hits the satellite in the same direction as the instant velocity vector of the satellite. The ...
2
votes
2answers
104 views
Is Earth's orbit around the sun affected by the ~8 minutes light delay?
Gravitational change occurs at the speed of light. As a consequence, we experience on Earth the gravitational attraction of the sun based on its position relative to us ~8 minutes ago. How does this ...
0
votes
2answers
76 views
How to calculate time for ball to reach plane while considering mass, gravity and wind resistance?
The scenario that I'm having is such that a ball of radius $15mm$ is thrown from a location point $\vec{p}=(2, 5, 2)$ in a direction of $\vec{d}=(3, 0, 4)$. The initial velocity is $30m/s$. There were ...
1
vote
5answers
137 views
How universal gravitation falls short
As a non physicist I can understand how Newtonian mechanics falls short in cases of high velocity etc. and is properly generalized by the special theory of relativity.
What is not clear to me is how ...
-1
votes
2answers
81 views
How to determine Center of Gravity? [closed]
I came across this question while having conversation with one person.
We know that Center of Gravity of a solid cube is at the intersection of connecting the opposite vertex of the cube.
Suppose, you ...
2
votes
2answers
83 views
Parabolic motion (experiment)
We performed a laboratory, performing six releases of a sphere with angles $15^\circ,30^\circ,45^\circ,60^\circ,75^\circ,40^\circ$ a parabolic movement, took five distances for each angle, the initial ...
3
votes
2answers
58 views
Two-body problem questions
I am self studying the two body problem and I'm stuck on the following:
I have given $$\ddot{\vec{x}}_1= - G m_2 \frac{\vec{x}_1-\vec{x}_2}{|\vec{x}_1-\vec{x}_2|^3}$$ and $$\ddot{\vec{x}}_2= - G ...
3
votes
2answers
141 views
Theoretical need for Newtonian Gravity
I've been wondering:
Are there, still, some advantages, for current research, to study Newtonian gravity? I mean, not experimentally, where Newton gravity is a very good approximation to everyday ...
8
votes
3answers
311 views
Is it possible that 5 planets can revolve around a single star in a single orbit?
I'm writing a novel and I'm quite confused if this system could be possible in the real universe. Is it possible that a system exist, where 5 identical planets which could be of same characteristics ...
1
vote
2answers
144 views
Semi-major axis and ellipticity of a binary system?
In the image below (source at bottom), it seems to be suggesting that
\begin{equation}
a = a_{1} + a_{2}, \hspace{8cm}(1)
\end{equation}
where $a_{1}$ and $a_{2}$ are the semi-major axis of the ...
3
votes
1answer
75 views
How do I calculate how something should stay in position under gravity?
Excuse me if this too simple a question - I'm not a regular (consciously) user of physics.
I have a ship in space and it is under the effect of three moons. The ship can rotate and thrust to move ...
0
votes
1answer
79 views
Has anyone on Earth ever seen the dark side of the moon and if so where are the pictures? [duplicate]
If the Moon rotates then we should see the dark side right? But as far as I know the Moon only shows one side to Earth, how can this be if it is rotating?
3
votes
1answer
78 views
Units for physical constants
Someone told me that units for $G$ and $\epsilon_0$ (gravitational constant and Coulomb's constant) are placed there simply to make equations work dimensionally and that there is no real physical ...
0
votes
1answer
102 views
Earth's rotation isn't that orbit?
If the earth is rotating at some $465~\text{m}/\text{s}$ at the equator and that's really fast.
Shouldn't we in that case be in orbit with the earth just not fast enough?
How fast do we need to ...
4
votes
2answers
116 views
If the moon was rapid enough would it be able to orbit the earth from a close distance?
If the moon was close in orbit that it's surface was like 100 km away from the earth's surface. And it had a large enough angular velocity will it be able to hold orbit?
If this was possible, is ...
2
votes
3answers
137 views
Is Newtonian gravity consistent with an infinite universe? [duplicate]
Let us assume that we have have an infinite Newtonian space-time and the universe is uniformly filled with matter of constant density (no fluctuations whatsoever), all of it at rest. By symmetry, the ...
0
votes
2answers
54 views
Saturn ring stabilization
The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System.
I'm wondering, what power is primarily responsible for that stability?
© Public Image by NASA ...
7
votes
4answers
482 views
What causes a soccer ball to follow a curved path?
Soccer players kick the ball in a linear kick, though you find it to turn sideways, not even in one direction. Just mid air it changes that curve's direction. Any physical explanation?
Maybe this ...
0
votes
3answers
99 views
Solve for Initial Velocity of a projectile given Angle, Gravity, and Initial and Final positions?
I've found equations http://www.physicsclassroom.com/Class/1DKin/U1L6a.cfm for solving everything (and rearranged to solve everything) to do with projectile motion EXCEPT this, even though it should ...
1
vote
3answers
111 views
Projectiles and escape velocity
Q: The escape velocity for a body projected vertically upwards from the surface of earth is 11 km/s. If the body is projected at an angle of $45^\circ$ with vertical, the escape velocity will be?
...
5
votes
2answers
80 views
Gravitational potential outside Lagrangian points or Lagrange points
The diagram in Why are L4 and L5 lagrangian points stable? shows that the gravitational potential decreases outside the ring of Lagrange points — this image shows it even more clearly:
If I ...
1
vote
1answer
77 views
Gravitational field v.s. Physical variable?
I went to a talk on Newtonian mechanics some time earlier and the speaker said, and I quote,
Newton's equations of motion admit a larger symmetry group than the Galilean group alone. Therefore, ...
0
votes
1answer
64 views
What Speed Would an object need to leave the earth at to reach L1? [closed]
Let's say the Earth is an airless sphere. What speed would an object weighing 1 kg need to leave the surface at in order to get to and be motionless at L1, where the Moon's gravity becomes stronger ...
0
votes
0answers
57 views
How much energy would it take to move the asteroid that has been implicated in the dinosaur extinction by a few centimeters? [closed]
One of the greatest mass extinctions occurred about 65 million years ago, when, along with many other life-forms, the dinosaurs went extinct. Most geologists and paleontologists agree that this event ...
10
votes
4answers
571 views
Is Feynman's explanation of how the moon stays in orbit wrong?
Yesterday, I understood what it means to say that the moon is constantly falling (from a lecture by Richard Feynman). In the picture below there is the moon in green which is orbiting the earth in ...
1
vote
4answers
248 views
Why do objects accelerate as they fall?
Most importantly, what must change in order for the falling object to change its speed? Is it the distance to the centre of the planet? If you pull the earth away from the object as the object falls, ...
1
vote
1answer
52 views
Simulating an orbit, primary is not at focus
I've been toying around with some -very- simple orbital simulators, mostly using preexisting physics libraries (I took a layman's stab at doing it with vectors too). The thing that is confusing me is ...
1
vote
2answers
134 views
So gravity turns things round
It makes sense, since gravity tends to push the surface of a body towards it's center. Unless I'm mistaken, everything with mass has it's own gravity, every atom and for instance, our own bodies ...
0
votes
2answers
69 views
Kinetic energy with no velocity
When a body is displaced against the gravitational field of force it gains potential energy. When we drop the body it begins to move downward with a certain amount of acceleration, and the potential ...
