Spring in Space: 3 Questions Answered

[chazemz]

I would like to ask some questions. I am in a spacecraft (I have grip on the floor) and at one end a spring is attached to the wall. I hold the spring and begin to walk backwards, extending the spring.
1) What will happen to the spacecraft as I walk backwards?
2) What will happen to the spacecraft when I let go of the spring?
3) What will happen to the spacecraft when the spring has returned to its original state?

 

[Drakkith]

1. The spacecraft moves in the opposite direction.
2. The spring and the spacecraft oscillate in opposite directions for a bit (assuming the spring can oscillate in both directions and isn't fully compressed in its resting state).
3. The spacecraft will have moved backwards slightly relative to yourself.

 

[gianeshwar]

I think all due to conservation of linear momentum as there is no external force.
Will the same happen if spacecraft is falling vertically down in gas friction free space i.e in gravity field(conservative force field).

 

[jbriggs444]

I think all due to conservation of linear momentum as there is no external force.
Will the same happen if spacecraft is falling vertically down in gas friction free space i.e in gravity field(conservative force field).

Is the gravitational field uniform? If so then adopt a coordinate system in which the spacecraft is at rest and use the previous answer.

 

[chazemz]

Changing the spring to a magnetic field. If I have a horseshoe magnet and distort the magnetic field between the poles. If I suddenly remove the distorting force, since the magnetic flux lines contain elastic potential energy, will the flux lines behave like a slinky, ie move backwards and forwards (oscillate) across the original steady state line until coming to rest?

 

[Drakkith]

Changing the spring to a magnetic field. If I have a horseshoe magnet and distort the magnetic field between the poles. If I suddenly remove the distorting force, since the magnetic flux lines contain elastic potential energy, will the flux lines behave like a slinky, ie move backwards and forwards (oscillate) across the original steady state line until coming to rest?

I think they'll just return to their original position without an oscillation, but I'm not sure. I also think this will set up an EM wave that propagates outwards from the spacecraft .

 

[sophiecentaur]

Changing the spring to a magnetic field. If I have a horseshoe magnet and distort the magnetic field between the poles. If I suddenly remove the distorting force, since the magnetic flux lines contain elastic potential energy, will the flux lines behave like a slinky, ie move backwards and forwards (oscillate) across the original steady state line until coming to rest?

It all depends on the details of the mechanical arrangement. I am not sure exactly what you had in mind but 'in principle'. If there is some restraint on the magnet and the magnetic object it is attracting then you could either have the situation of a spring in which the coils are all in contact when it's unloaded, in which case the load will just hit the end stop, the ship will move back to its original position. If the rest position for the magnetic arrangement will allow the magnet to move both sides of it (as with a spring where the coils are not touching when relaxed) then you could have some harmonic motion but EM radiation causes it to decay (slowly) The ship would also move but, of course, the displacement would be inversely proportional to the relative masses of sprung mass and ship. The position of the CM will not ever change as a result of these activities.

 

[chazemz]

It all depends on the details of the mechanical arrangement. I am not sure exactly what you had in mind but 'in principle'. If there is some restraint on the magnet and the magnetic object it is attracting then you could either have the situation of a spring in which the coils are all in contact when it's unloaded, in which case the load will just hit the end stop, the ship will move back to its original position. If the rest position for the magnetic arrangement will allow the magnet to move both sides of it (as with a spring where the coils are not touching when relaxed) then you could have some harmonic motion but EM radiation causes it to decay (slowly) The ship would also move but, of course, the displacement would be inversely proportional to the relative masses of sprung mass and ship. The position of the CM will not ever change as a result of these activities.

Sorry, I have started this all wrong. Please ignore the spacecraft . What I am trying to understand is what will happen to the field flux lines between the stator poles of a dc motor when the load is suddenly withdrawn.
When load is applied to the motor, armature reaction means that the stator flux lines will distort. If this load is suddenly taken away, will the flux lines simply return to the no load position or will they distort slightly on the other side? If they just shorten, will they cause an effect on the stator (apply a force) since there must be a release of energy?