What sound would a giant ball of weaponized plasma make when it flies through the air at high speed?

Yeah... topic. I tried a Google search and got a bunch of stuff about the speed of sound.

On that note, what would it sound like when it hit and melted a large area of ground, buildings, machines, and people half a kilometer away? I didn't have to worry about this earlier because of the lack of sound in space.

If the weaponised glob of plasma was contained (which it has to be) it would sound no different to any other projectile shell as it passed.

Plasma melting a large area wouldn't be acid and screaming. Depending on how quickly the energy was released, it'll be a massive explosion due to sudden release or a great fizzing like a plasma cutter. The screaming starts later, when people are blinded and burned on the outskirts of the initiation.

I never faced combat myself, but one of my sergeants who fought in Vietnam once said he could hear the difference between different types of bullets as they flew by and that twenty years later he still remembered each one.

Assuming the target is advanced enough to have radar or better, the authorities will try to warn the public to run for shelter. So the first sound would be what? Sirens? A chorus of cell phones? Follow this with the sounds of footsteps and panic. I imagine the weapon would ignite high in the air with an eerie silent flash. As it approaches, a sonic boom would echo around the target area drowning out the previous sounds, followed quickly by flames crackling like an enormous campfire. Only this one roasts people instead of marshmallows. The impact would be about the same as any other explosion. The funny thing is that buildings and debris don’t fall at the same time. If you’ve seen footage of a controlled skyscraper demolition you know what I mean. Multiply that sound by however big your target and your weapon is. Finally, add the sound of frightened, injured, confused and angry survivors if any.

If only there were some terrestrial phenomenon that we could compare it to ... something like a massive electrical discharge with energies on the order of 500,000 megajoules, something that turns the air through which it passes to plasma ... something like ...

Lightning.

I don't know what the moving plasma ball itself would sound like, but I'd be willing to bet that it would be accompanied by a pretty hellacious thunderclap, and for the same reasons.

Thanks, all. This will be quite helpful.

I feature a plasma weapon in my story. I had it contained in an artillery shell that causes impact damage and cracks open, causing crackling arcs of electrical discharge which kill humans and disrupt circuitry etc.
Trying to hurl plasma through the air and still have it remain as a ball just won't work, because it will interact with the air and disperse or try to attain electical equilibrium with its surroundings. You need some sort of containment device or field.

Good point. Later on I changed it to be contained within a metal sphere. I might change it again.

In the void of space, would that effect be increased or decreased?

Take a paper bag, inflate it with air, and then twist it shut. Now throw it in a campfire. There will be a "whoomph" sound when the inside of the back catches fire. That is sort of what I imagine it to be like.

I would think that the original sound you were asking about would be similar to what's fired from a roman candle, although much louder and greater Doppler effect from it's speed.

it would probably ound like a plasma cutter

http://science.discovery.com/videos/deconstructed-plasma-cutter.html

"Lightning.

I don't know what the moving plasma ball itself would sound like, but I'd be willing to bet that it would be accompanied by a pretty hellacious thunderclap, and for the same reasons."

if lightning is crossing your path you get BANGas it turns water vapor into steam instantly.

if it's coming straight at you it sounds like shoook - shooook SHOOOOK!

It may not be scientifically accurate, but I imagine it not having a sound at all. You just hear the incredibly loud mechanicals of the weapon. Clack-Chick, something like that.

I would imagine it as loud. Like sonic boom loud.

I'm doing a scifi adventure right now and one of the characters is a cyborg shock trooper who uses a "ball lightning gun", which is basically a shotgun that fires plasma orbs instead of shot or slugs. Upon impact with anything with significant mass (or after a few milliseconds) the magnetic field containing the plasma pops and the energy is released. This includes heat and a miniature shockwave. It's basically the equivalent of a thermite charge AND breaching charge hitting you. Even armored opponents get melted quite horrifically. The heat is enough that the water in people can vaporize instantly, making them explode. Such weaponry is banned on many worlds as they are considered "uncivilized". And because the guns are incredibly dangerous to use. The soldier can only use it as her body was literally redesigned for attrition combat. An unshielded human firing it would melt their own skin off if they fired it at someone too close.

I describe the sound of the orbs blowing as being more or less identical to the thunder another character heard as a kid on her homeworld. The blast also releases a blinding light (the cyborg's eyes screen it) that further disorients the next poor bastard while she lines up his blast. It's actually possible to muffle the shots of the weapons in this universe, but the character doesn't bother with hers. She was designed to instill terror in enemies, and feels the thundering sound is appropriate. This becomes a problem at one point when she is in a cramped alleyway with an ordinary human nearby. Firing her main weapon would shatter the girl's eardrums.

"phewm!"?

1) Plasma is physical material and thus has mass (unlike a laser), which, given the speeds at which it is fired to maintain such a high energy state, will have enormous kinetic impact.
2) To maintain a "ball" of plasma is impractical without some containment. A "ball" means that particles are travelling in all directions within a sphere, but are also being redirected back towards the center of the mass, thus necessitating a magnetic or physical "containment"
3) A plasma weapon would send a projectile much like a very long bullet or laser beam out of its barrel. the "ball" would look much like a bullet, if you could even see it at it's enormous velocities, and might sound like lightning (silent, followed by a concussive re-collapse of the atmosphere) along it's entire trajectory.
4) The sound of such an impact might be an enormous concussive strike, like an artillery shell of incredible energy, combined with the destructive force of explosive expansion from contact with super-heated materials.