text: An empirical approximation for this force includes a term for one hundred over the Hazen-Williams constant, all raised to the 1.85 power.
full_question: An empirical approximation for this force includes a term for one hundred over the Hazen-Williams constant, all raised to the 1.85 power. The magnitude of this force is often expressed as a factor K times v squared over two g, as seen in the full Colebrook equation. A factor measuring this force exactly equals 16 over the Reynolds number if the Reynolds number is small. The nondimensional "epsilon over diameter" is plotted against Reynolds number on a Moody plot to estimate Fanning's factor to measure this force. It usually provides the error between both sides of the Bernoulli equation. Long, straight, rough pipelines require pumps to counteract head losses due to it. For 10 points, name this force that opposes the motion of fluids in pipes.
first_sentence: An empirical approximation for this force includes a term for one hundred over the Hazen-Williams constant, all raised to the 1.85 power.
raw_answer: pipe friction [prompt on pressure head losses or pipe roughness]