This evening I was digging a hole for a post. Deep in the hole it was very dark. The digging bar I was using would send off large orange/red sparks when it hit a rock. Being the amateur physicist that I am. I thought, wow, those are about 650 nanometer waves. But, I knew no magnetic lines of flux were cut. I also knew that when an electron is moved to a higher orbit and then falls back down EM waves are generated. So was my bar actually stripping electrons away. What was going on?


It is the same as the way flint lighters work, steel hitting "rock" .

Iron, whether man-made objects or naturally occurring in rocks, will rust upon exposure to oxygen in the air. The act of rusting is actually an exothermic reaction called “oxidation”, which is a fancy way of saying when iron touches the oxygen in the air a reaction occurs; the iron rusts (turns into iron oxide) and gives off heat. In other words, it burns. The simplified chemical reaction can be expressed as:

Fe2 + O2 = Fe2O3 + heat

Or in simple English: Iron + Oxygen = Rust + Heat


Small Particles Have Larger Surface Area – As can be seen in this illustration, the total surface area of the smaller cubes greatly exceeds the surface are of the cube taken as a whole.When a tiny particle of fresh iron is broken off from the main mass, the surface area of the particle is very large in comparison to its total size.Upon contact with oxygen in the air, the tiny iron spontaneously ignites (also known as rusts or oxidizes) and glows red hot.

On the atomic level of the broken off cubes, black body radiation mechanisms are involved, transitions in vibrational and rotational levels of the molecules and at the tail of the black body distribution electron excitations and deexcitations.The initial energy is supplied by the chemical proccess: iron oxide is at a lower energy level than pure iron +O2.

  • $\begingroup$ Hmmm.... electron excitations and deexcitations .... hmm... so I am I correct in saying that all EM waves are generated by the electron moving. There maybe different ways to move the electrons, but it's their movement that is the source of all EM radiation. I hope you say yes because that would say something beautiful about the universe. $\endgroup$ – Lambda Oct 5 '16 at 5:07
  • $\begingroup$ Is the equation "Iron + Oxygen + Heat = Rust + Much more heat and the reaction is rapid due to the elevated temperature created by friction? Also does the rock have to contain iron to get a spark? $\endgroup$ – Farcher Oct 5 '16 at 5:32
  • $\begingroup$ It has to be a hard rock in order to break off the iron crystals. There will be some heat energy on the tiny blocks from the energy of the motion of the digging bar, but most of the energy goes into breakin off the small block from the large lattice. At the microscopic level friction of small blocks is ignorable, as it is the energy difference between free iron and bound into an oxide that is large. $\endgroup$ – anna v Oct 5 '16 at 5:44
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    $\begingroup$ @Farcher If you read the article you will see that iron catches fire, that is what exothermic means . It just has to meet oxygen. On large surfaces it just turns iron to rust. The surface to area of the small block of the lattice reacts on all sides, the heat takes the small block to visible black body temperatures and light is emitted by that process by the tail of the distribution. All fires are fast. $\endgroup$ – anna v Oct 5 '16 at 6:51
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    $\begingroup$ @annav Thank you for being so patient with me. I now understand the process. $\endgroup$ – Farcher Oct 5 '16 at 6:57

These are probably the same sparks

a small fiery particle thrown off from a fire, alight in ashes, or produced by striking together two hard surfaces such as stone or metal

produced when sharpening a steel tool on a grinding wheel. The metal particles are so hot from the impact that they oxidise. You can see this effect by sprinkling iron filings into a flame. They could also be particles of pyrite (FeS2)

late Middle English (denoting a mineral used for kindling fire): via Latin from Greek puritēs ‘of fire,’ from pur ‘fire.’

which can oxidise. Robert Hooke investigated this.


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