# Questions tagged [orbital-motion]

The path a body takes while moving through space under the influence of the gravitational forces of other bodies

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### Isn't the velocity in an orbit always tangential, not radial and tangential?

In this video the person resolves the momentum vector into two components, tangential and radial. But isn't the velocity at every point on the orbit tangential?
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### Rotational mechanics $u$-substitution

In classical physics, when we try to get the force as a function of $r$; Why do we substitue $$r=\frac{1}{u}?$$ I don't get it, what is the point of it? Is the substitution arbitrary? I am looking ...
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### What is the distance from the Earth where the centripetal force would equal the gravitational force?

I've been trying to find the length of an unbendable and unbreakable tether of zero mass extending off the surface of the Earth with a mass at its end, where the centripetal force would equal the ...
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### Where does the energy from tidal power plants come from? [duplicate]

Tidal power plants taps into the energy in the motion of the oceans due to the gravitational interaction between the earth and the moon, so much is clear to me. This question is about where would this ...
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### How does the shape of a planetary body affect the orbit of its moon?

More specifically, would the distortion from a sphere of the planetary body lead to shifts in angular momentum for the moon.
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### Reason for inertia of motion of Earth orbiting the Sun [duplicate]

We all know the following universal truth since childhood. Earth (and other planets) orbits around the Sun. And, while I was reading this post, I found that the reason behind Earth revolution is ...
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### Orbits within orbits

Do galaxy clusters have structured orbits (e.g. ellipticals)? If not, why not? Moons orbit planets, planets orbit stars, and stars orbit galactic centres. Is there something different about the ...
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### Can we ever calculate the exact period and semi-major axis for an orbit with strong perihelion precession?

To calculate the period of an orbit with strong perihelion precession we could just pick an arbitrary point in the sky, and time how long it takes for it to pass it again. But wouldn't we get ...
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### Schwarschild Metric from Kepler law

Can we redrive Schwarschild metric from Kepler's law without assuming General Relativity?
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### Centripetal Acceleration to find Orbital Velocity

When presented with a problem asking for the orbital velocity of an object $1,000 km$ above the Earth's surface, the formula I know you can use is $$v=\sqrt{\frac{G*m}{r}}$$ However, I was thinking ...
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### Since astronomers are adding 'leap seconds' to our years nowadays, does that mean Earth's orbital period is getting longer?

How long was an Earth year several billion years ago? (I'm assuming constant days, even though I know days were much shorter back then).
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### Is spacetime in an ellipse around a massive object, or does it just slope down towards the massive object?

In some discussions, people seem to imply that spacetime is in an actual ellipse around a massive object so that, for example, the planet orbiting a star is actually traveling in a straight line in ...
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### Can a single electron have an orbital angular momentum in the direction of propagation in free space?

I trying to understand the article about quantized orbital angular momentum in electron vortex beams. The article is not important per se, as there are many others. But I'm reading it as if an ...
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### What would happen to the Moon if the Earth stopped providing it with a centripetal force owing to its force of gravity?

Would the Moon really only travel in a straight line then? What about the other planets and their forces of gravity? Wouldn't they prevent this rectilinear and undisturbed motion of the Moon?
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### How do astronauts and spacecrafts float away into space if they're always under the influence of the Earth's gravity? [duplicate]

I understand that as the distance between the planet and the body increases, the gravity decreases, but how can they still just 'float away'?
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### How to prove Kepler's 3rd law? [duplicate]

How to prove Kepler's 3rd law? How did Kepler proved it? Is it possible to prove the third law without applying Newton's universal law of gravitation?