Well, once the egg instantly comes out of the shell its a liquid. And once the liquid touches the heated pan, it starts to form a solid.
~But why is this? Its quite simple actualy... Well, all eggs contain protein (such as albumin) which consists of long chains of amino acids.
And when these proteins are heated, they denature. What is this you may ask? It simply means that while the amino acid chains remain intact, the weak bonds and attractions between different parts of the chain are forced apart and the protein loses its shape, becoming more-or-less just a straight chain.
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Also, think about it... When the liquid touches the pan, it starts a chemicle reaction which then links all the chemicals into a more or less solid material.
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~Hope this helped :)
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