I want to know why an induction heater and an induction ring launcher don't produce the same effect. Both seem to use AC voltage to power a solenoid(which induces a voltage in a pipe) so why doesn't the induction heater launch the pipe inside it, or the induction launcher just heat the "projectile" pipe.
Induction launcher https://www.youtube.com/watch?v=szPwPLNN4IM
Induction heater https://www.youtube.com/watch?v=_v5Hg2zfLjs
Both seem to use AC voltage to power a solenoid(which induces a voltage in a pipe) so why doesn't the induction heater launch the pipe inside it, or the induction launcher just heat the "projectile" pipe.
Both effects happen but, there's a vast swathe of middle ground that reduce one effect and enhance the other. To get a launcher you want losses in the target ring to be very low so that it's reactionary magnetic field is quite high. This causes a launch and very little heating.
In the induction heater, you want losses in the "material" to be quite high so that heating takes place and, accordingly, mechanical reaction is quite low.
Three substantial differences:
For a given amount of power delivered to the material (voltage * current induced in it), the flux density, in the magnetic field doing that induction, is inversely proportional to frequency (Faraday's law). Lorentz force (magnetic component) is in turn proportional to flux density: \$\vec{F} = \vec{v} \times \vec{B}\$. Thus, force is inversely proportional to frequency, at a given power level and for given material and geometry.
There are, of course, induction heaters operating at lower frequencies, and at such power levels, that they deliver significant forces, whether to cause material displacement (requiring clamping to constrain the work, or that causes stirring of a melt), or enough to overcome gravity and levitate or launch a workpiece wholesale.
Note that there is no threshold between cases, it is a continuum between low and high power levels, low and high resistivity materials, and low and high frequencies. Whether some combination of those variables is enough to cause some given effect, is another matter, but the underlying physics at work do not care about any such threshold.
As for pulsed operation, consider this: a typical implementation might use a capacitor discharge circuit into a coil of wire. The coil and workpiece are positioned such that there is an easy path for them to push apart (whereas a workpiece in the middle of a solenoid coil for example, won't go much of anywhere, if centered properly that is). A typical example is a pancake coil and a plate/ring; another is the cored solenoid in the video, with the ring positioned so that there is more flux density behind it. (Where this position lies, compared to the primary coil itself, depends on the shape and size of the core; it's not obvious from a glance at the video, how the core is shaped inside the base.)
A capacitor discharge circuit can produce massive currents, developing flux densities of several tesla peak even without the help of a magnetic core (indeed, no materials saturate above 2T, so a core is only of modest value at these levels anyway!). Equivalent frequencies can be in the 100s Hz to 10s kHz, which may be on the high side, but this is made up for by the sheer violence that is possible. When many kJ of energy is involved, the peak power level can be near gigawatts, and the forces can be enough to radially pinch a small disc -- a "quarter shrinker" machine for example.
Compare to a typical induction heater circuit: the available current is, at most, either what is available from the AC power supply directly (current-sourcing type), or from the resonant capacitors and Q factor (voltage-sourcing type).
The common ZVS circuit is of the voltage-sourcing type. The push-pull transistors act as a synchronous power mixer ("mixer" in the RF sense), converting supply voltage to AC output voltage. Conversely, this converts AC current flow into DC supply current, so that load resistance manifests as DC resistance at the inverter's supply; thus, DC power is drawn when AC power is dissipated into a workpiece (as must necessarily be the case).
Thus we can conclude, the Lorentz force available from such a circuit, is limited by supply voltage, capacitance, and coil geometry.
To be able to use such a circuit as a launcher, as much power must be drawn from the supply as is delivered to the load -- whether by resistive dissipation or mechanical work. Presumably, several kilowatts are desired, to have a satisfyingly impactful demonstration? This will require quite large transistors, and a power supply capable of at least as much peak power (a regular power supply unit won't do, but a battery perhaps could). The elephant in the room, however, is the capacitors required to reach low enough frequencies to be useful. Which have the effect of increasing the resonant current (the ratio of AC voltage to circulating current is given by \$Z_0 = \sqrt{L/C}\$), but also reducing the Q factor (because the coil has about the same resistance but proportionally less reactance). Eventually you're putting far more power into the coil's resistance, just to make a pitiful magnetic field, than you are into actually pushing the work (and needless to say, you want to avoid heating the work; use copper or aluminum). The coil resistance can be mitigated by adding a magnetic core to the system (which I believe is what the unit in the video clip uses), but at this point you're just making a transformer with extra steps, and you can just plug it into the wall (a ready source of 50/60Hz AC) briefly to do the job.
So, suffice it to say, there isn't much meaningful connection between a toy induction heater module, and something useful for propulsion. While the effects are identical, the circuit and geometry changes are substantial enough that a different engineering solution becomes apparent.
