Can Angular Momentum Create Forward Movement?

[Xilus]

OK so a trust can produce a torque,
But two torques can't produce a thrust?

There is no way to convert angular momentum into forward momentum.

 

[mfb]

There is no way to convert angular momentum into forward momentum.

Correct.
It is symmetric: There is also no way to convert forward momentum to angular momentum.

External forces (like thrusters on a spacecraft ) can change both forward and angular momentum at the same time.

 

[A.T.]

OK so a trust can produce a torque,
But two torques can't produce a thrust?

You can have a net force, without a net torque.
You can have a net torque, without a net force.

There is no way to convert angular momentum into forward momentum.

You need a net force, to change linear momentum.
You need a net torque, to change angular momentum.

 

[sophiecentaur]

Google Eric Laithwaite's name and see what happened to a perfectly capable Engineer when he got involved in this topic. The Establishment treated him as a Pariah, despite his being a giant in the field of MagLev. Reactionless drive ranks with Astrology and Homeopathy, unfortunately.

 

[A.T.]

Reactionless drive ranks with Astrology and Homeopathy, unfortunately.

There were some recent efforts by NASA to verify some tiny effects. But that has northing do with Laithwaite's misunderstandings of gyroscopes.

 

[anorlunda]

There is no way to convert angular momentum into forward momentum.

Not true. No mysteries here, just ordinary life. The ball throwing machine converts angular to linear. A bullet hitting the tail of the rooster converts linear to angular.

 

[sophiecentaur]

There were some recent efforts by NASA to verify some tiny effects. But that has northing do with Laithwaite's misunderstandings of gyroscopes.

But there is the same feel about the topic and I am waiting for NASA to say that the effects were due to experimental error. But who knows what the finer effects of GR could produce under extremes of gravity?

 

[sophiecentaur]

Not true. No mysteries here, just ordinary life. The ball throwing machine converts angular to linear. A bullet hitting the tail of the rooster converts linear to angular.

View attachment 114789

Do you happen to have any ball park figures on that experiment?
(But linear and angular momentum are both conserved in both cases.)

 

[A.T.]

The ball throwing machine converts angular to linear. A bullet hitting the tail of the rooster converts linear to angular.

Energy can be transferred between linear KE a angular KE, because it is the same physical quantity.

Linear momentum and angular momentum are different quantities, that aren't converted into each other. Each is conserved on it's own.

 

[mfb]

Not true. No mysteries here, just ordinary life. The ball throwing machine converts angular to linear. A bullet hitting the tail of the rooster converts linear to angular.

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Total linear and total angular momentum are conserved in both cases.

Google Eric Laithwaite's name and see what happened to a perfectly capable Engineer when he got involved in this topic. The Establishment treated him as a Pariah, despite his being a giant in the field of MagLev. Reactionless drive ranks with Astrology and Homeopathy, unfortunately.

And all those are against the forum rules.

 

[anorlunda]

Total linear and total angular momentum are conserved in both cases.

I stand corrected. Brain not working this morning.

 

[Xilus]

Do you guys think atomic physics like the LHC could lead to advanced propulsion?
How could something on the atomic scale relate to propulsion of large scale objects?

 

[mfb]

The LHC does not do atomic physics. The experiments there do nuclear and particle physics.

Atomic physics is important for ion thrusters, nuclear physics is important for radioisotope power sources and can become important for nuclear reactors in space (only prototypes so far).

 

[Xilus]

Slingshoting around a planet leads to acceleration (right?)
If you sling shot around two, would you end up with net acceleration in the same direction?

 

[sophiecentaur]

Slingshoting around a planet leads to acceleration (right?)
If you sling shot around two, would you end up with net acceleration in the same direction?

It works when the first sling shot sends the craft to catch up with the second planet. Each close encounter gives the craft extra momentum - but the detail of the trajectory is fairly critical. The gain in speed will be comparable with the 'forward' speed of the target planet; the orbit round the planet has to be hyperbolic so that the craft is not captured. Google "Slingshot Orbit" Images and see loads of pictures.

 

[Xilus]

gravity assist does leave with a net acceleration though right?
I think it imparts momentum on the planet in the opposite direction right?

 

[sophiecentaur]

gravity assist does leave with a net acceleration though right?
I think it imparts momentum on the planet in the opposite direction right?

You mean a net gain in momentum.
Momentum is conserved always.

 

[mfb]

I think it imparts momentum on the planet in the opposite direction right?

Sure, total momentum is conserved.
Please keep the discussion on topic, or start new threads for different questions.

The gain in speed will be comparable with the 'forward' speed of the target planet

Only in very rare circumstances. You can only gain velocity if the outgoing trajectory is closer to the orbital direction than the incoming trajectory. But every spacecraft motion we can get with current propulsion methods is close to circular orbits. The change in the angle cannot be large, which means the increase in speed cannot be large either, especially for the inner planets.

For the inner planets, you cannot gain their orbital speed even with arbitrary initial motion - their escape velocity is too low.

 

[Buckleymanor]

OK so a trust can produce a torque,
But two torques can't produce a thrust?

There is no way to convert angular momentum into forward momentum.

If you stood on a low friction platform which had the ability to rotate and held out an operating giro the platform and yourself would rotate.
You could connect the platform to geared wheels and the whole caboodle would move forward.

 

[sophiecentaur]

For the inner planets, you cannot gain their orbital speed even with arbitrary initial motion - their escape velocity is too low.

I don't understand that bit. Escape velocity refers to getting off the surface, doesn't it? The craft doesn't get that near does it and it is very small in proportion to any of the planet's mass.

 

[mfb]

I don't understand that bit. Escape velocity refers to getting off the surface, doesn't it? The craft doesn't get that near does it and it is very small in proportion to any of the planet's mass.

Imagine a tiny asteroid. How do you want to use it to change the spacecraft velocity by any significant amount?

The trajectory that changes the speed the most is just grazing the surface of the object, and a larger escape velocity means you can have a larger deflection at higher approach speeds.

 

[sophiecentaur]

Right. It's the gravitational potential that counts, of course.