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Modified example:
Hailstorm (with your car outside in it)
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Threshold for damage to car set by size of
individual hailstones
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Below threshold hailstones cause no dents
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Above threshold they cause bigger dents
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Number of dents = number of hailstones bigger than threshold
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Very unlikely two small hailstones can hit exactly
together to cause dent
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Real life example:
Ultra-Violet light hitting your skin
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Threshold for chemical damage set by energy
(wavelength) of photons
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Below threshold (long wavelengths) energy too weak to break bonds
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Above threshold (short wavelength) energy photons break apart DNA
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Number of molecules damaged = number of photons above
threshold
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Very unlikely two photons can hit exactly together to
cause damage
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