2

When a current-carrying rectangular loop is placed in a magnetic field, the forces acting on either side of the loop which is perpendicular to the field provides a torque which rotates the loop. enter image description here

However, according to Newton's 3rd Law, there should be some equal and opposite force acting on the object exerting the force. But in fields, it is the field that exerts forces on objects. Does that mean that the loop exerts an equal and opposite force on the magnet or on the magnet's field? How do these forces play out and what effect do they have on the magnet?

Mauricio
  • 5,273
latin333
  • 97
  • Interesting! As far as I know, Newton's laws were never meant for force-fields - they define force itself and acceleration as its consequence. Hail Oersted, for he unleashed the tormenting truth of fields (magnetic fields, though it was later generalized to all kinds of forces). – Awe Kumar Jha Feb 20 '21 at 05:51
  • I would rather suggest to read Faraday's or Maxwell's on the idea of lines of force. – Awe Kumar Jha Feb 20 '21 at 05:53
  • This is a great answer https://physics.stackexchange.com/questions/114466/apparent-violation-of-newtons-3-textrd-law-and-the-conservation-of-momen – xXx_69_SWAG_69_xXx Feb 20 '21 at 06:07
  • this wikipedia is pretty good as well https://en.wikipedia.org/wiki/Momentum#Electromagnetic – xXx_69_SWAG_69_xXx Feb 20 '21 at 06:21
  • Fleming's right hand rule described that flow of electrical current in the loop (flipping the bird sign) will induce a magnetic field acting on the magnetic field from the permanent magnet (reprimanding sign) which then result in a magnetic force (compliment sign) so it is 2 magnetic fields battle royale ;D – user6760 Feb 20 '21 at 06:34
  • Try operating a generator or motor without bolting it to the floor. Make sure you are nowhere close when you turn that contraption on. We don't want you to get injured or worse. Of course the fields transfer the torque and momenta. This, by the way, was already obvious in Newtonian gravity. It is expressed in the symmetry of the force law. Whatever force the sun exerts on Earth, Earth exerts on the sun. – FlatterMann Apr 19 '23 at 21:14

1 Answers1

1

Newton's third law does cause magnets to have equal and opposite effects on each other, whether electromagnets or permanent magnets. The equal and opposite forces are transferred by the magnetic field. In an electric motor or generator, just as the field magnets are pushing /pulling on the armature via their magnetic fields, the armature is also pushing / pulling the field magnets. If you hold a small electric motor in your hand when it is started you can feel the anti spin ward torque of the motor housing as it applies spinward torque on the armature.

Adrian Howard
  • 8,513