What exactly are sparks scientifically?

[Pengwuino]

So what exactly are sparks in theri scientific sense? Are they really hot pieces of metal flying off or large amounts of light coming off or what?

 

[cepheid]

I think that the sparks you see when a train suddenly hits the breaks or whatever (steel wheels on steel rails) are little glowing bits of metal heated to high temps by friction and thrown in all directions.

Spark, if I remember right, also has another connotation. What you see in a darkened room if you get a shock from static electricity. Or, the spark plug in a car. Basically I think it refers to whenever you make electrons "jump the gap", and that produces visible results. I'm open to corrections though.

 

[Danger]

I'm open to corrections though.

Any mechanical spark, as in the train scenario you mentioned, or a bench grinder, is indeed a piece of material heated to incandescence and ejected from the point of origin. An electrical spark consists of plasma which has been created from the atmosphere by the heat involved in the electric current. It's like a little neon bulb, but since the air is primarily nitrogen, it glows purplish rather than red.