# The Naked Scientists Forum

### Author Topic: Acceleration and magnetism  (Read 2069 times)

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3756
• Thanked: 46 times
• The graviton sucks
##### Acceleration and magnetism
« on: 31/12/2014 21:11:57 »
If two bar magnets were held together south pole to south pole or visa versa in the absence of any other fields and then released would they start moving away by accelerating and then reach an equilibrium velocity or continue accelerating to infinity.

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4490
• Thanked: 137 times
• life is too short to drink instant coffee
##### Re: Acceleration and magnetism
« Reply #1 on: 31/12/2014 23:57:51 »
F = Ma

If F > 0 then a > 0

F = B1B2/r2 > 0 for all r

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3756
• Thanked: 46 times
• The graviton sucks
##### Re: Acceleration and magnetism
« Reply #2 on: 01/01/2015 00:33:38 »
F = Ma

If F > 0 then a > 0

F = B1B2/r2 > 0 for all r

Thanks

#### evan_au

• Neilep Level Member
• Posts: 3934
• Thanked: 224 times
##### Re: Acceleration and magnetism
« Reply #3 on: 01/01/2015 10:41:40 »
If the magnets were in space, but fixed in alignment via a hypothetical taut string of infinite length and zero friction, then they would continue accelerating forever. With an acceleration force which declines with the square of distance, if they start off with a non-zero initial separation (determined by the physical size of the magnets), then I expect they will asymptotically approach a finite separation velocity.

However, in practice, if the magnets were in space with no alignment mechanism and released, they would flip around so they are facing North to South poles, and clamp together, reaching zero acceleration and zero velocity immediately.

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3756
• Thanked: 46 times
• The graviton sucks
##### Re: Acceleration and magnetism
« Reply #4 on: 01/01/2015 16:43:18 »
If the magnets were in space, but fixed in alignment via a hypothetical taut string of infinite length and zero friction, then they would continue accelerating forever. With an acceleration force which declines with the square of distance, if they start off with a non-zero initial separation (determined by the physical size of the magnets), then I expect they will asymptotically approach a finite separation velocity.

However, in practice, if the magnets were in space with no alignment mechanism and released, they would flip around so they are facing North to South poles, and clamp together, reaching zero acceleration and zero velocity immediately.

That's an interesting conclusion.

#### The Naked Scientists Forum

##### Re: Acceleration and magnetism
« Reply #4 on: 01/01/2015 16:43:18 »