Principles Of Friction Loss Flashcards
First Principle of Friction Loss
Friction loss increases or decreases directly with the length of the hose or pipe, assuming all other conditions are the same.
How does the length of a hose affect friction loss if other conditions remain constant?
If the hose length doubles, friction loss doubles; if the length triples, friction loss triples. This is because friction loss is directly proportional to the length of the hose or pipe, meaning longer hoses result in greater resistance to water flow.
Why does the First Principle specify “all other conditions are the same”?
The phrase ensures that factors like hose diameter, flow velocity, or pressure do not change. If any of these vary, they could affect friction loss, making it impossible to isolate the effect of length alone on friction loss.
What practical implication does the First Principle have for selecting hose length?
To minimize friction loss, use the shortest hose possible for a given task, as a longer hose will increase friction loss proportionally, reducing the efficiency of water delivery.
Second Principle of Friction Loss
Friction loss increases approximately with the square of the flow velocity when hoses are the same size, and velocity is proportional to flow.
How does doubling the flow velocity affect friction loss according to the Second Principle?
If the flow velocity doubles, friction loss increases by approximately four times (2² = 4), because friction loss is proportional to the square of the velocity. This shows that small increases in velocity lead to large increases in friction loss.
Why does the Second Principle apply only when hoses are the same size?
The principle assumes the hose diameter remains constant, as changes in diameter would affect friction loss (per the Third Principle). By keeping the hose size the same, the principle isolates the effect of velocity on friction loss.
How does the relationship between velocity and flow impact the Second Principle?
Since velocity is proportional to flow, increasing the flow rate increases velocity. Thus, if the flow rate doubles, the velocity doubles, and friction loss increases by approximately the square of that increase (four times), highlighting the significant impact of flow rate on friction loss.
Third Principle of Friction Loss
For the same discharge, friction loss decreases as the hose diameter increases, inversely proportional to the 5th power of the diameter.
What happens to friction loss if the hose diameter is doubled, assuming the same discharge?
If the diameter doubles, friction loss decreases by a factor of 32 (2⁵ = 32), because friction loss is inversely proportional to the 5th power of the diameter. This shows that larger diameters significantly reduce friction loss.
Why does the Third Principle specify “for the same discharge”?
The same discharge means the flow rate (volume of water per unit time) remains constant. This ensures that any change in friction loss is due to the change in diameter, not a change in the amount of water flowing through the hose.
What is the practical significance of the 5th power relationship in the Third Principle?
Small increases in hose diameter lead to dramatic reductions in friction loss. For example, a slight increase in diameter can make a hose much more efficient, as the 5th power relationship amplifies the effect of diameter changes on friction loss.
Fourth Principle of Friction Loss
For a constant flow velocity, friction loss remains approximately the same, regardless of the water pressure in the hose.
How does water pressure affect friction loss according to the Fourth Principle?
Water pressure has little to no effect on friction loss if the flow velocity remains constant. This means that whether the pressure is high or low, the friction loss depends primarily on the velocity of the water, not the pressure pushing it.
Why is velocity the key factor in the Fourth Principle, rather than pressure?
Friction loss is caused by the resistance of water moving against the hose walls, which is determined by how fast the water moves (velocity). Since velocity is fixed in this principle, friction loss remains consistent, even if pressure varies.
What does the term “approximately” imply in the Fourth Principle?
The term “approximately” suggests that while pressure has a minimal effect on friction loss at a given velocity, there may be slight variations due to real-world factors (e.g., hose material or minor turbulence), but these are not significant enough to change the principle’s core idea.
