Let's imagine some very powerful dude with absolutely ridiculous strength/speed/durability. I'm not asking about the credibility of this, let's suppose it's magic. He's got some magical sword as durable as it need to be (probably way more than the hardest thing we can think of today. Here again, let's say it's magic). It would be 115 cm long.
Now the real question : If this guy strikes air with his sword at a very high speed, what would be the effects ? Sounds, shockwaves, light, sparks, fire, plasma ? In which amplitude ?
To clear up the ambiguity left by the "very high speed" expression, please give me your advice about these 3 orders of magnitude :
- Speed of sound (~300 m/s)
- 10 times the speed of sound (~3000 m/s)
- Half of the light speed (~150 000 000 m/s)
Let's say it's the instantaneous speed of the tip of the sword. We're on earth, same atmospheric pressure, same gravity, at sea level.
I'm looking for some cool effect without obliterating the entire world, so I'm looking for the best speed for that. I'm hungry for maths too, if possible.
Feel free to give me your advice about how to make things even funnier if possible. Keep in mind that I'm very well conscious of the ridiculousness of the situation.