Re: Give Me A Break. Could It Be More Obvious?
Generally, I agree with everything quoted below but I figured I'd clear up a few things.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Rapidly bend a piece of copper back and forth until it breaks, or hammer flat a piece of copper on an anvil, and the molecular friction created will cause the copper to get hot, sometimes hot enough to burn skin.</div></div>
It's true that bending a piece of metal will create heat (see: work/strain hardening) and the heat affects the energy state of the e- in Cu (in this case) but that's the only thing happening at the molecular level. The heat you would be feeling in this scenario is created by friction at the crystal level which is the difference between a single piece of sand vs. the planet Jupiter in the chemistry world.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Copper will burn. The easiest way to see this, and in the form of "sparks", is add energy by shorting out copper wires with an electrical impulse the wires can't handle. The sparks you see are not some magical form of eletrical mystery, they are hot, burning pieces of copper flying in all directions. </div></div>
Cu won't burn but it will melt and as it cools down some of the heat energy is given off in the form of light which is what you're seeing in any spark. Cu sparks loose energy too fast to be considered 'hot' this is also why Cu is such a great conductor and why Cu is used in 'sparkless' tools. It's helpful to think of Cu's cold sparks more as sworf/grindings than sparks. This is also why Cu sparks for all intents and purposes don't really exist which is also why it is accepted that Cu doesn't spark and there are a lot of other metals that don't spark.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Copper is a major component in welding processes, the mig wire I use at work contains copper, if you've ever mig welded then you know all about welding sparks. My plant is full of robotic spot welders. Spot welder tips are copper, need to be "dressed" every so often to clean off the oxidation, and are consumable to the point of being replaced several times during a day's production. Sparks launching from the robots on nearly every weld they make is a common scene all across the floor of the shop. The composition of these sparks certainly contains some of the steel base metal being welded, but even with simple common sense knowledge that the copper electrodes degrade rapidly, it's evident that the sparks would also contain copper.</div></div>
The Cu tips your talking about are being melted away and are no doubt flying off as a small portion but mixed with some other sparking metal and may not even be considered sparks in some cases. The steel sparks would be hot sparks but the Cu looses its energy too fast to be considered hot. In terms of sparks, oxides of Cu are immaterial.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The root of this discussion is energy; electrical energy wih the welding and the over loaded extention cord creating heat, mechanical energy creating friction heat in the rapidly bent copper, and kinetic energy creating heat in the hammered flat copper. Kinetic energy is what we have with a bullet striking something hard enough to make a "spark". </div></div>
Agreed, but bear in mind it's not the Cu from the bullet creating the spark that's capable of starting a fire, it's the target material.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The faster the energy is <span style="color: #FF0000">created, </span>the more concentrated the heat is, the more visable the reation is....as in "spark".</div></div>
Energy is transferred from the bullet to the target, not created.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">As with anything though, you would need the right combination of conditions and events to get a "spark" from a bullet. <span style="color: #FF0000">Since it is actually the combustion of the bullet/target</span> it stands to reason you would need a high enough velocity to initiate enough heat, and you would need dry enough conditions to allow the burn to take place. Obviously a low velocity hit under damp conditions likely wont produce any "sparks". </div></div>
Cu doesn't burn so we're not talking about burning or combustion. The only combustion going on is of oxides and that's immaterial in terms of this discussion. Damp, dry, hot, or cold conditions are immaterial as no matter the circumstances, Cu cools off too fast to be a fire hazard (unless it's ~1900F at your shooting range).
