BRAINCAKEEstimation and Orders of Magnitude
The order of magnitude of a quantity is its size given to the nearest power of ten. For example, 2 × 105 J has an order of magnitude of 105 J. Orders of magnitude let you compare very different sizes quickly: an atom is about 10−10 m across and a nucleus about 10−15 m, so an atom is about 105 times wider than its nucleus.
An estimate is an approximate value found using sensible, rounded values for the quantities involved. Estimates are usually worked to one significant figure. They let you check whether a calculated answer is sensible and answer questions where exact data are not available.
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All 12 lessons in Measurements and Errors · All AQA AS-level Physics topics