What is the difference between intrusive and extrusive rock

The major visible difference between the two are crystal size, intrusive rocks have a larger crystal/grain texture due to the slow cooling of magma below the earth surface which encourages the growth of larger crystals, while extrusive rocks, because of the rapid cooling at/above the earth's surface does the opposite.

Explanation:

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it also supports my hypothesis. if you rest first you can squeeze the clothespin more times. from the data i collected the average of the eight people concluded exercise makes your muscles more fatigued and less able to squeeze the clothespin compared to resting before squeezing.