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A comment on Twisted graphene has become the big thing in physics. Parent comment

Re:Twisted graphene has become the big thing in physics by Arbalest on Friday May 03, 2019 @02:12AM (#19815980)
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.

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Re:Twisted graphene has become the big thing in physics by mrpgraae on Friday May 03, 2019 @03:14AM (#19816230)
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.

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Re:Twisted graphene has become the big thing in physics by ouid on Friday May 03, 2019 @02:55AM (#19816165)
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.
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Re:Twisted graphene has become the big thing in physics by soulofmischief on Friday May 03, 2019 @05:43AM (#19816884)
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.
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Re:Twisted graphene has become the big thing in physics by garmaine on Friday May 03, 2019 @06:02AM (#19816961)
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.
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Re:Twisted graphene has become the big thing in physics by Arbalest on Friday May 03, 2019 @06:43AM (#19817146)
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.
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