1) It is easy to become confused by poor or incorrect choices of units of measur

Question

1) It is easy to become confused by poor or incorrect choices of units of measure. The following statements were found in the geological literature, suggesting that not all geologists use consistent units. For each statement point out the unitary inconsistency and rewrite the statement using SI units.

a) "The force of gravity at sea level is approximately 980 dynes per square centimeter."

b) "In practice, force is often expressed in terms of grams or grams per square centimeter or in pounds or pounds per square inch."

Explanation / Answer

a) "The force of gravity at sea level is approximately 980 dynes per square centimeter.

the unitary inconsistency is that the unit force should be in dynes not in dynes per square centimeter

force should be in dynes

SI unit of force is Netwon (N)

we know that

1 Newton (N) = 10^5 dynes

so

force = 980 dynes

force = 980 x 10-5 N

force = 9.8 x 10-3 N

so the force is 9.8 x 10-3 N

the final statement should be

"The force of gravity at sea level is approximately 9.8 x 10-3 Newton (N) .

b) "In practice, force is often expressed in terms of grams or grams per square centimeter or in pounds or pounds per square inch."

force is not expresses in grams or grams per square centimeter

force is also not expresses in pounds or pounds per square inch

the correct statement should be

"In practice, force is often expressed in terms of Newton (N)   or pound force (lbf) ."

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