0
$\begingroup$

I watched a video of a toy car moving with 2 magnets, one bigger than the other. The answer I received was that the video was real, the toy car indeed moves.

So, I was wondering, if an object with 2 magnets or electromagnets (eg opposite charge facing each other) is in space, without friction, would the object move provided the magnets never touch, never move from their position, and they don't demagnetize?

If, on the contrary, a friction surface (eg. track) would need to exist for the objet to move in space, why is that? I have a hard time to understand it.

I'm aware similar questions have been addeed to Stackexchange, but I haven't seen any question referring to two superconducting magnets or electromagnets of different size/intensity in outer space.

Also, according to wikipedia:

In Maxwell electrodynamics, Newton's third law does not hold for particles. Instead, particles exert forces on electromagnetic fields, and fields exert forces on particles, but particles do not directly exert forces on other particles. Therefore, two nearby particles do not always experience equal and opposite forces.

Improve this question
$\endgroup$
4
  • 6
    $\begingroup$ From time to time there are questions here about propulsion involving special arrangements of magnets, but the answer is always the same; momentum and energy are conserved, there's no free lunch, etc. If the video appeared to violate those or to provide "free energy" or "perpetual motion" then there's something else going on that's not shown or mentioned. The video could be real, and the car might have moved, but that doesn't mean all the information is there to understand what moved it. $\endgroup$
    – uhoh
    Commented Nov 5, 2020 at 6:38
  • 2
    $\begingroup$ the car could have been propelled by the magnets through the earth's magnetic field. if so a spacecraft could do this too, provided it was within the earth's magnetosphere $\endgroup$
    – R. Hall
    Commented Nov 5, 2020 at 6:49
  • 3
    $\begingroup$ It is hard to explain why the video might work, without seeing it or without a good explaination what is seen. (Basically everything beside someone push/pulls magnet A and magnet B is following should be considered as fake: you have been fooled). I once saw a youtube video of someone who tried do get free movement with magnets. It doesn't work at first, he changed stepwise the arrangement. In the end, he was so proud he made it, that he did not realise, he reinvented an DC-motor and needed electrical power to run it. $\endgroup$
    – CallMeTom
    Commented Nov 5, 2020 at 6:49
  • 2
    $\begingroup$ @ReubenFarley-Hall There's a similar idea to this: en.wikipedia.org/wiki/Electrodynamic_tether. This uses conductive tethers rather than magnets, but it does involve interacting with a planetary magnetic field. $\endgroup$
    – Pitto
    Commented Nov 5, 2020 at 11:03

1 Answer 1

Reset to default
7
$\begingroup$

Any method of propelling a spacecraft needs two things:

  • Something to push against, which is usually propellant ("reaction mass") that is expelled, but also can be matter existing in space such as solar wind, tenuous interstellar gas, or even light.

  • A source of power. This can be either inside the spacecraft or outside of it.

If you don't have both of those, the spacecraft will not accelerate.

There is a method of using a magnet to propel a spacecraft: a Magnetic Sail. These consist of only one magnet in most configurations, and that magnet has to be very lightweight, but absolutely huge -- basically a ring of electromagnet wire. The solar wind flowing out from the sun is made of charged particles, so it is deflected by the magnetic field and pushes it, providing both something to push against and a source of power.

This is a very slow method of propulsion and it only works to push you, very gently, away from the sun. Surprisingly, it's actually possible to navigate through much of the solar system this way (and it's faster than a solar sail) but very, very slow.

Other than that... if there's not something to push against, and no source of power... no spaceship.

Improve this answer
$\endgroup$
1
  • 2
    $\begingroup$ The car in that video is just using the magnets to make a magnetic spring. It would work just as well with a rubber band...and be as useful for satellite propulsion as a rubber band. $\endgroup$
    – Christopher James Huff
    Commented Nov 5, 2020 at 15:33

Not the answer you're looking for? Browse other questions tagged or ask your own question.