[amp_mcq option1=”sudden enlargement” option2=”sudden contraction” option3=”gradual contraction or enlargement” option4=”friction” correct=”option4″]
The correct answer is D. friction.
Friction is the force that opposes the relative motion of two surfaces in contact. It is caused by the roughness of the surfaces, which interlock and catch on each other. The amount of friction depends on the materials of the surfaces, the force pressing them together, and the roughness of the surfaces.
In a long pipe, friction occurs between the fluid and the walls of the pipe. The fluid molecules rub against the wall of the pipe, and this friction causes the fluid to lose energy. The more friction there is, the more energy the fluid loses.
Sudden enlargement and sudden contraction of a pipe can also cause a loss of energy. When the fluid flows through a sudden enlargement, it has to accelerate to fill the larger space. This acceleration causes the fluid to lose energy. When the fluid flows through a sudden contraction, it has to decelerate to fit into the smaller space. This deceleration also causes the fluid to lose energy.
However, the loss of energy due to friction is much greater than the loss of energy due to sudden enlargement or sudden contraction. Therefore, the major loss of energy in long pipes is due to friction.