3 ms·

I'm definitely not an expert, but just because you need force to go around corners doesn't mean you need work. An unchanging magnetic field in fact exactly acco

by ouid 8y ago

I'm definitely not an expert, but just because you need force to go around corners doesn't mean you need work. An unchanging magnetic field in fact exactly accomplishes this, as it always accelerates an electron perpendicular to its motion, thereby leaving the energy of the electron unchanged.

Arbalest 8y ago
That sounds a lot like a slingshot maneuver around a planet to get more momentum. Strictly speaking you're taking energy from the planet/sun to do so. An unchanging magnetic field still exists in the real universe, and I find it difficult to believe that it would be completely unaffected by the interaction. fwiw I'm also no expert edit: I'm taking unchanging to be a practical implementation of say a permanent magnet here, rather than a theoretical construct.
- ouid 8y ago
  no, what I'm talking about is more like a perfectly circular orbit around the sun, where the direction of the acceleration is always exactly perpendicular to the motion.
  - soulofmischief 8y ago
    But there is no perfectly circular orbit around the sun. The mass of the two bodies causes the center of mass to be slightly off center from the sun, and both the sun and earth orbit around this center of mass in a fashion that AFAIK loses energy.
    - garmaine 8y ago
      If the two objects were either perfect spheres or tidally locked, then a circular orbit would continue forever. There are no losses due to pure motion in a vacuum.
      - Arbalest 8y ago
        I thought the theme of my reply is that we're not talking about theoretical constructs, but instead reality... Space is not a vacuum, just much lower pressure than on earth.
- mrpgraae 8y ago
  It is clearly possible to change the direction of an objects movement without doing work on it, if you consider forces perpendicular to the direction of movement. In other words, you can change the direction of the velocity vector without doing work, as long as the magnitude stays the same (ignoring potential energy here). In fact, a magnetic field is unable to do work, since it always acts perpendicular to the direction of movement of the charge that it acts upon.

by ouid 8y ago

Arbalest 8y ago

That sounds a lot like a slingshot maneuver around a planet to get more momentum. Strictly speaking you're taking energy from the planet/sun to do so. An unchanging magnetic field still exists in the real universe, and I find it difficult to believe that it would be completely unaffected by the interaction. fwiw I'm also no expert edit: I'm taking unchanging to be a practical implementation of say a permanent magnet here, rather than a theoretical construct.

ouid 8y ago
no, what I'm talking about is more like a perfectly circular orbit around the sun, where the direction of the acceleration is always exactly perpendicular to the motion.
- soulofmischief 8y ago
  But there is no perfectly circular orbit around the sun. The mass of the two bodies causes the center of mass to be slightly off center from the sun, and both the sun and earth orbit around this center of mass in a fashion that AFAIK loses energy.
  - garmaine 8y ago
    If the two objects were either perfect spheres or tidally locked, then a circular orbit would continue forever. There are no losses due to pure motion in a vacuum.
    - Arbalest 8y ago
      I thought the theme of my reply is that we're not talking about theoretical constructs, but instead reality... Space is not a vacuum, just much lower pressure than on earth.
mrpgraae 8y ago
It is clearly possible to change the direction of an objects movement without doing work on it, if you consider forces perpendicular to the direction of movement. In other words, you can change the direction of the velocity vector without doing work, as long as the magnitude stays the same (ignoring potential energy here). In fact, a magnetic field is unable to do work, since it always acts perpendicular to the direction of movement of the charge that it acts upon.