# Tag Info

### Can perfectly stable orbits exist in GR?

In the literature, the orbits you are looking for a called “floating orbits”. Floating orbits are not possible in plain GR (See e.g. 1302.1016).
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### Can perfectly stable orbits exist in GR?

As you say, GR implies that all orbits lose energy (very slowly) over time, due to gravitational waves. Also the vacuum of space is not true vacuum and there is some drag from the intergalactic medium ...
• 6,596

### Can perfectly stable orbits exist in GR?

In the 1979 paper "Time without end", Freeman Dyson calculates a time in the order of 1020 years until the earth would fall into the sun due to gravitational decay alone, based on the ...
• 365
Accepted

### How accurate does the ISS's velocity and altitude need to be to maintain orbit?

For a particular orbital period and altitude (or altitude and eccentricity, or eccentricity and period), there is exactly one velocity that produces the correct orbit. Of course the ISS doesn't have ...
• 782
Accepted

### How to calculate jerk in uniform circular motion?

Consider the trajectory $$\vec{r} = r \begin{pmatrix} \sin(\omega t) \\ \cos(\omega t) \end{pmatrix}$$ Differentiate once \vec{v} = \omega r\begin{pmatrix} \cos(\omega t) \\ -\sin(\omega t) \end{...

### What would happen to the moon's orbit if we reduce (instantaneously) its mass?

Mass is a conserved quantity. Having it simply disappear violates the known laws of physics. Once you have violated the laws of physics you can no longer ask what the laws of physics predict, since ...
• 104k
Accepted

### Doubt on conservation of angular momentum for Kepler's laws

The definition of a plane can be written as $\vec{a}\cdot \vec{r} = 0$, where $\vec{a}$ is any vector perpendicular to the plane. In this case, you have a vector quantity $\vec{L}$, which is from its ...
• 133k

### Doubt on conservation of angular momentum for Kepler's laws

The angular momentum ${\bf L}$ of a point-like particle is proportional to the vector product of position ${\bf r}$ and velocity ${\bf v}$. It is a vector orthogonal to the plane containing ${\bf r}$ ...
Accepted

### Is any planets angular speed roughly constant?

Depends on how close "roughly constant" is. Yes other bodies can influence the earth's rotation. The moon has the biggest long-term effect as the oceanic tides it raises helps to couple ...
• 41.3k

### Tilting due to Earth's rotation at a distance

If you stand on a high tower, the velocity on the top is greater, than at the bottom, since the angular velocity is the same. So if you drop a stone it has compared to the bottom a relativ velocity ...
• 6,440

### Why particle is certain to escape the conservative field when the mechanical energy is positive?

From the comments: By @naturallyInconsistent For convenience, we chose to put the conventional dividing line for this thing so that zero is the limiting case. i.e. it is a choice, a very natural ...
1 vote

### The Circular Orbital Velocity Relative to a Stationary Observer in Schwarzschild Geometry

A sketch of the full proof is as follows: Take the effective potential in terms of the specific angular momentum $L/m$ and differentiate it with respect to $r$. Equate this to zero to find that the ...
• 133k
1 vote

### Which type of trajectory would an object take in the below stated case?

If the sun is the only mass attracting the object, and it isn't moving in your reference frame, and then you release the small object "from rest" the object will follow a linear trajectory ...
• 121
1 vote

### When does electrostatic effect failed and needs quantum mechanics?

Accelerated charges radiate energy, and a circular orbit implies constant acceleration and constant energy. Thus, a stable circular orbit for a charged particle is incompatible with classical physics....
• 46.5k

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