What are similarities and differences of the 1st, 2nd, and 3rd class levers?

Similarities:
-- All three classes have a fulcrum (pivot).
-- All three classes have a point where the effort force is applied.
-- All three classes have a point where the load or resistance force is applied.
-- If you can find a place to stand and a lever that's long enough,
then you can move the Earth with a 1st or 2nd Class lever.

Differences:
-- The mechanical advantage of a 1st Class lever
can be greater than 1, equal to 1, or less than 1.
-- The mechanical advantage of a 2nd Class lever is always more than 1 .
-- The mechanical advantage of a 3rd Class lever is always less than 1 .

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