Forces from sparks and Newton laws...

[Externet]

Hi.

Another video 😉 but short and no need to see it all;  just time stamp 0:30 shows the spheres shaking.  How is the spark producing forces ?  I could imagine if they where suspended, the motion would show greater.

----> https://www.youtube.com/watch?v=s8704VbBKbw

[Bufofrog]

Here that crack noise from the spark?  I assume that pressure wave is what is making the spheres move.

[Externet]

Thanks. 

Seems then the sudden heating of air from the spark expands the air and the 'crack' sound wave produces the shaking of the spheres.  Acoustic motor 🙄 like windows in  thunder.