If the Earth stopped spinning? (orbiting the Sun)

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Discussion Overview

The discussion revolves around the question of why the Earth does not fall into the Sun, exploring concepts of angular momentum and orbital motion. Participants examine the relationship between the Earth's motion, its angular momentum, and gravitational forces, while also referencing the Moon's behavior in relation to the Earth.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the Earth has angular momentum due to its orbital motion around the Sun, which prevents it from falling into the Sun.
  • Others argue that the Earth's spin around its own axis is unrelated to its orbital motion, suggesting that only orbital angular momentum is relevant.
  • A participant presents an analogy involving a rubber band and a tennis ball to illustrate their view on the Moon's motion and its relationship with Earth, emphasizing orbital motion over angular momentum.
  • Another participant challenges the analogy, stating that gravity behaves differently than a rubber band, as gravitational force decreases with distance.
  • Some participants discuss the Moon's tidal locking and its implications for angular momentum, asserting that the Moon does possess angular momentum due to its rotation.
  • There is mention of the coupling of angular momentum between the Earth and Moon due to tidal effects, which affects the Moon's orbit over time.
  • One participant suggests that if the Earth were to become locked in its orbit, it could eventually fall into the Sun, raising questions about the nature of orbital dynamics.
  • A later reply introduces the idea that the Earth is continuously falling towards the Sun but follows a curved path due to the curvature of space, preventing it from actually reaching the Sun.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the roles of angular momentum and orbital motion in preventing the Earth from falling into the Sun. The discussion remains unresolved, with no consensus reached on the nature of these forces and their implications.

Contextual Notes

Some statements reflect assumptions about the nature of gravity and angular momentum that may not be universally accepted. The discussion includes various analogies and models that may not fully capture the complexities of gravitational interactions.

avito009
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Why does the Earth not fall into the sun? Is it because Earth has angular momentum? or is it because the Earth has orbital momentum?
 
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Both. It has angular momentum about an axis passing through the Sun due to its orbital motion. You could call this orbital angular momentum. It also spins around its own axis, but that is unrelated to its orbital motion.
 
Drakkith said:
Both. It has angular momentum about an axis passing through the Sun due to its orbital motion. You could call this orbital angular momentum. It also spins around its own axis, but that is unrelated to its orbital motion.
why angular momentum.The moon is tidal locked so no angular momentum is applied. I believe that the moon get pulled in and swings out to the other side and get further away and repeats. Picture this, a cut rubber band attached to a tennis ball and swing it over your head. The rubber band acts like the gravity while the tennis is the moon and the hand is the earth.You see, the moon did not get pulled in by the rubber band but as it pulls in, it moves forward and continue to fall away from the Earth but the Earth grab it and so on and so on.Orbital motion i think is the reason. Correct me if i am wrong as it is my observation.
 
Neon said:
why angular momentum.The moon is tidal locked so no angular momentum is applied. I believe that the moon get pulled in and swings out to the other side and get further away and repeats. Picture this, a cut rubber band attached to a tennis ball and swing it over your head. The rubber band acts like the gravity while the tennis is the moon and the hand is the earth.You see, the moon did not get pulled in by the rubber band but as it pulls in, it moves forward and continue to fall away from the Earth but the Earth grab it and so on and so on.Orbital motion i think is the reason. Correct me if i am wrong as it is my observation.
Interesting, but a few small details could be refined.

Angular momentum is not a torque.

The rubber band does have a tension force when stretched, and the force will increase with more of the more the stretch.
Gravity on the other hand decreases with distance. Gravity is entirely not like a rubber band.
 
Neon said:
why angular momentum.The moon is tidal locked so no angular momentum is applied.

Angular momentum is not applied. It is like linear momentum in that it is a conserved quantity associated with movement.
 
Neon said:
why angular momentum.The moon is tidal locked so no angular momentum is applied.
The moon rotates around its axis. Anything that rotates around its center of mass has angular momentum
 
256bits said:
The rubber band does have a tension force when stretched, and the force will increase with more of the more the stretch.
Gravity on the other hand decreases with distance. Gravity is entirely not like a rubber band.
Nothing else acts like gravity.
 
Hello? Any more comments?
 
Neon said:
Nothing else acts like gravity.

OK I will bite ... in what way do you think nothing else act like gravity ?
how about expanding on your comment and we can see if you are correct or if you just misunderstandD
 
  • #10
string does not act like gravity because well you should know.Basically nothing that is elastic and the tension gets weaker the more it gets pulled.
 
  • #11
Neon said:
string does not act like gravity because well you should know.Basically nothing that is elastic and the tension gets weaker the more it gets pulled.
There is no reason why you couldn't make a device that would follow ISL for force / extension. It would be very possible if the device had 'active' control (power supplied from the central pivot) . Of course, it would not be 'elastic' but that wouldn't matter if you just wanted to produce an elliptical orbit with it. Come to think of it. I'm surprised I haven't seen this at some Science Exhibition; they all seem to make do with the conventional tapered bowl with balls orbiting round.
To hard for a School Demo piece of equipment, though.
 
  • #12
phinds said:
The moon rotates around its axis. Anything that rotates around its center of mass has angular momentum
Let us suppose the moon did not rotate around it's own axis even though from Earth it would look like it does.This property would not cause the moon to fall into the Earth any more than the Earth would fall into the sun if it behaved in a similar manner.
It is the orbital rotation of the Earth around the sun irrespective of it's angular momentum about it's own axis which stops it falling into the sun.
 
  • #13
Buckleymanor said:
Let us suppose the moon did not rotate around it's own axis even though from Earth it would look like it does.This property would not cause the moon to fall into the Earth any more than the Earth would fall into the sun if it behaved in a similar manner.
It is the orbital rotation of the Earth around the sun irrespective of it's angular momentum about it's own axis which stops it falling into the sun.
The fact that the Moon and Earth are not homogenious spheres means that the angular momentum of each of them becomes relevant. The tidal effects between the two is causing the angular momentum of their individual rotations to be coupled to the angular orbital momentum. The effect is that the Moon's orbit around the Earth is very slowly increasing in radius. So you cannot completely separate the rotational and orbital momenta.
 
  • #14
sophiecentaur said:
The fact that the Moon and Earth are not homogenious spheres means that the angular momentum of each of them becomes relevant. The tidal effects between the two is causing the angular momentum of their individual rotations to be coupled to the angular orbital momentum. The effect is that the Moon's orbit around the Earth is very slowly increasing in radius. So you cannot completely separate the rotational and orbital momenta.
I agree but as far as the op is concerned it's about a decrease in radius rather than an increase.:smile:
Would the Earth eventualy fall into the sun if it became locked in it's orbit.
 
  • #15
Buckleymanor said:
Let us suppose the moon did not rotate around it's own axis even though from Earth it would look like it does.This property would not cause the moon to fall into the Earth any more than the Earth would fall into the sun if it behaved in a similar manner.
It is the orbital rotation of the Earth around the sun irrespective of it's angular momentum about it's own axis which stops it falling into the sun.
I was simply responding to the issue of whether or not the moon has angular momentum. Do you argue that it does not? I was not addressing anything about orbits.
 
  • #16
avito009 said:
Why does the Earth not fall into the sun? Is it because Earth has angular momentum? or is it because the Earth has orbital momentum?
Ask your self this: How could it?
It is moving at 60,000mph perpendicular to the direction of the sun. How would you cancel this momentum?
 
  • #17
phinds said:
I was simply responding to the issue of whether or not the moon has angular momentum. Do you argue that it does not? I was not addressing anything about orbits.
Obviously from my reply I regard it does have angular momentum .Mt reply was just an attempt to bring the thread back on topic as far as all the op questions.
 
  • #18
avito009 said:
Why does the Earth not fall into the sun? Is it because Earth has angular momentum? or is it because the Earth has orbital momentum?
the Earth is falling into the sun - but it is falling in a straight line in curved space so it never gets there - try imaging it from the side you would see a corkscrew path
 

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