Physics Help Forum Given this doesn't work; why?

 General Physics General Physics Help Forum

 Oct 17th 2018, 05:50 PM #1 Junior Member   Join Date: Oct 2018 Posts: 25 Given this doesn't work; why? I'm only trying to see if two magnets with differnt mass and strength can be made to move in space structured together. I thought newton's third law would explain it. I got side tracked. I'm sure the answer is no. I would think I should know what the law is That says the answer is no. Sent from my LG-M210 using Tapatalk
 Oct 18th 2018, 01:16 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,080 Is this the answer you were looking for? Perhaps we could re-phrase your question, could two magnets be made to orbit each other? I am guessing that if you arranged for the magnets to rotate such that their opposing poles were always aligned at the same time as they orbited their common centre of mass at the perfect speed such that the centripetal acceleration matched the force of magnetic attraction... It might be theoretically feasible, but it would be a hugely finely balanced arrangement, which would collapse given the slightest nudge. __________________ ~\o/~
 Oct 18th 2018, 01:31 AM #3 Junior Member   Join Date: Oct 2018 Posts: 25 Sorry. What I was thinking was: Take a magnet of X mass, aligned with another magnet with the similar pole, repulsion force between the two. Second electromagnet force is dialed up or down with a mass of y. Bolted a distance apart. The electricity is stored to turn the second mass y- into a more less magnetic force. You would need to structure the rest of the arrangements to make motion possible, with the greater mass perhaps being pushed away carrying the lesser part with. If any kind of structure can be arranged to take advantage of motion. Then what would the values of x y and the strength involvment. I suppose it would reach a stationary balance if bolted together with matter... What were you thinking that u said might be feasible? Sent from my LG-M210 using Tapatalk
 Oct 18th 2018, 01:50 AM #4 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,080 Magnetic Propulsion Its action and reaction again. To get something to move, something else has to change. So in the case of your magnets, what is it that they are changing to cause their movement? In space there are charged particles (cosmic rays, the solar wind, etc...) these charged particles do react to magnetic fields. It might be (theoretically) possible to use the magnetic fields to move these charged particles, and thus produce motion of the magnets in reaction. However the practical engineering difficulties would be significant... __________________ ~\o/~ Last edited by Woody; Oct 18th 2018 at 05:30 AM.
 Oct 19th 2018, 02:38 AM #5 Junior Member   Join Date: Oct 2018 Posts: 25 i thought a force was a source of causing a change, like the magnetic feild that exsist was simply a constant force surrounding the magnets suppling change in a feild around in. so the magnetic feild is a static force...of what though? maybe if we start off slow with the electricty supplied, and kept a consistant increace in supply, then the magnetic feild would conintuscly increase, and as the static feild is constantly expanding, it would need to somehow much a smaller mass away that is attached to carrying the source with...? thought it might work if the smaller mass had less force or some combination. . Sent from my LG-M210 using Tapatalk
 Oct 19th 2018, 11:33 AM #6 Senior Member   Join Date: Aug 2010 Posts: 434 I read the question as this: you have two magnets such that the mutual magnetic fields cause force F between them. One has mass m1, the other has greater mass m2. If they were sitting in open space one would move away with acceleration F/m1, the other with acceleration F/m2. But in this case, they are attached to a frame so neither can move away from the other. NO, they and the frame do NOT move, in the direction of the lighter with acceleration F/m1- F/m2. What does happen is that each applies force F to the frame, in opposite directions. There is no external force so the system, magnets and frame, does not move.
 Oct 22nd 2018, 06:40 AM #7 Junior Member   Join Date: Oct 2018 Posts: 25 I'm sure I knew already they wouldn't move move cuz they are bolted together in a frame. I'm trying to learn why exactly.. Or which law comes into play first. There doesn't need to be an external force to cause things to move obviously. Just space to move. That there is space to move is a given for the reason to achieve something to move If you don't know which law to refer me to or for me to learn Can u tell me what you meant by eternal force is needed to move something? Sent from my LG-M210 using Tapatalk
 Oct 22nd 2018, 01:52 PM #8 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,354 I think what you're looking for is this: what law states that two objects do not move relative to each other if they are bolted to a rigid frame with a fixed distance between them, even though they have a repelling force acting between them. The answer is Newton's second law of motion, which for this example can be stated as: $\sum {\vec F} = m\vec a$ Here the sum of forces acting on each magnet is the magnetic repulsive force F_m, which is acting in a particular direction, plus the restraining force from the frame, which is of the same magnitude as F_m and is acting in the opposite direction. Thus the sum of forces acting on each magnet is $\sum \vec F = \vec F_m - \vec F_m = 0$ Hence from Newton's second law the acceleration $\vec a$ for each magnet must be zero, which means each magnet maintains its original velocity , which is 0 measured relative to each other.