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Forgive me in advance for not being 100% accurate in my explanation. I am not an electrical engineer, nor have I academically studied physics, algebra, or anything of the sort.

So without further ado:

Let's say if I have a saucer made out of a light ferromagnetic metal sheet...If I put a device in it that creates an electromagnetic pulse aimed below and around the saucer, wouldn't the electromagnetic pulse (EMP) repel against the ferromagnetic material and push it up like a coil gun? https://en.wikipedia.org/wiki/Electromagnetic_pulse

"When a current flows through a conductor in a magnetic field, an electromagnetic force known as the Lorentz force, pushes the conductor in a direction perpendicular to the conductor and the magnetic field." https://en.wikipedia.org/wiki/Electromagnetic_propulsion

The EMP created below and around the craft acts as a coil gun, propelling its ferromagnetic body like going through a copper coil. https://en.wikipedia.org/wiki/Coilgun

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  • $\begingroup$ en.wikipedia.org/wiki/Solar_sail “Light has momentum and thus can exert pressure on objects.” $\endgroup$
    – G. Smith
    Commented Sep 28, 2020 at 0:02
  • $\begingroup$ Like poles of magnets repel each other, but they can only lift one by increasing the weight of the other equally per action and reaction. $\endgroup$
    – Adrian Howard
    Commented Sep 28, 2020 at 2:42
  • $\begingroup$ G.Smith, I think you're referring to ionic propulsion, using the ionic wind and radio frequencies to ionize particles as a form of thrust. That is not the case with my question. This radiates electromagnetism around itself, acting as as a pulsed coil to magnetically shoot it's ferromagnetic body through it. $\endgroup$
    – user6579
    Commented Sep 28, 2020 at 12:11

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As long as the electromagnetic device you put into the saucer is attached to the saucer, the recoil it will generate in response to emitting the pulse will cancel any force which the pulse might exert on the saucer, and no propulsion will result.

This is akin to trying to propel a boat by blowing wind into its sail using a fan that is attached to the boat's deck.

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  • $\begingroup$ Actually, you can propel a boat that way. It's not as efficient as turning the fan around and blowing it out the back of the boat, but it works, as long as the sail can reflect the wind backwards. I've built such a sail board as a demo. $\endgroup$
    – pwf
    Commented Sep 28, 2020 at 5:31
  • $\begingroup$ Do you have any documentation you could share? Surely the fan pushes the sailboat back at least as much as the reflected wind pushes it forwards. Where is the extra energy coming from? $\endgroup$
    – iCodeSometime
    Commented Sep 28, 2020 at 11:59
  • $\begingroup$ Ah, maybe depending on the angle? If the fan is blowing up more towards the sail, much of it's force would be downward, so if the sail was reflecting more directly rearward, I suppose that makes sense $\endgroup$
    – iCodeSometime
    Commented Sep 28, 2020 at 12:01
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    $\begingroup$ @iCodeSometime Mythbusters did it in Blow Your Own Sail. The physics is counterintuitive, but makes a whole lot more sense if you replace the sail with a U shaped tube that captures all of the air. This basically turns the fan into a ducted fan that's pointing backwads, and obviously will cause forward motion. As long as the net movement of the air is backwards, conservation of momentum will drive you forward. $\endgroup$
    – Cort Ammon
    Commented Sep 28, 2020 at 22:03
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    $\begingroup$ The reason it ends up being counterintuitive is that our brain isn't very good at keeping track of the air after it's hit the sail, so we sort of forget about the second half of the system (the air leaving the sail and entering the airstream). But if we collect all of the numbers and equations carefully, there's no violations of laws here. $\endgroup$
    – Cort Ammon
    Commented Sep 28, 2020 at 22:04

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