Query 7

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course Phy 122

2/11 2305hrs

Question: query introset How do we find the change in pressure due to diameter change given the original velocity of the flow and pipe diameter and final diameter?

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Your Solution:

I am assuming that the geight or depth remains the same, just like the last query question, you can take any cross section of the pipe, in that length your dealing with and figure the change in pressure, given the velocity and diameter (initial and final). The area of your specific cross section (like a cut through the specific section you are looking to measure) will be proportional to the velocity of the water in that section.

confidence rating #$&*:

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Given Solution:

** The ratio of velocities is the inverse ratio of cross-sectional areas.

Cross-sectional area is proportional to square of diameter. So velocity is inversely proportional to cross-sectional area:

v2 / v1 = (A1 / A2) = (d1 / d2)^2 so

v2 = (d1/d2)^2 * v1.

Since h presumably remains constant we have

P1 + .5 rho v1^2 = P2 + .5 rho v2^2 so

(P2 - P1) = 0.5 *rho (v1^2 - v2^2) . **

Your Self-Critique: I should have stated inversely proportional, but I think that is what I meant.

Your Self-Critique Rating:3

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I do believe that is what you intended.

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Question: query video experiment terminal velocity of sphere in fluid. What is the evidence from this experiment that the drag force increases with velocity?

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Your Solution:

The sphere accelerates with the addition of paper clips however, there is a definite drop in the value it accelerates starting at paper clip # 4 through 8. I expected it to pick up again once two paperclips were added at the same time but the acceleration seem to remain relatively the same. As questioned, I believe that the threshold of drag affecting acceleration was met. Now, I believe that with the addition of a lot more weight, the velocity will increase to a point where the balance mass would completely overtake the any resistance caused by the drag and it would simply be a matter of the counter weights mass and the acceleration of gravity. The slowing of the acceleration process is evidence that the drag force acting as resistance was having a big effect on the velocity.

confidence rating #$&*:

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Given Solution:

** When weights were repetitively added the velocity of the sphere repetitively increased. As the velocities started to aproach 0.1254 m/sec the added weights had less and less effect on increasing the velocity. We conclude that as the velocity increased so did the drag force of the water. **

Your Self-Critique:2

Your Self-Critique Rating: it took a few times reading and picturing this in order to wrap my head around it. I believe that I was trying to explain the same thing, just not as clearly.

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Question: `q001. If you know the pressure drop of a moving liquid between two points in a narrowing round pipe, with both points at the same altitude, and you know the speed and pipe diameter in the section of pipe with the greater diameter, how could you determine the pipe diameter at the other point?

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Your Solution:

At a constant altitude, gravitational acceleration remains the same so the change in the fluids velocity between two points in a flow can be correlated to the pressure change using Bernoulli’s equation. The pressure anywhere within the flow can be found using the nondimensional pressure coefficient C_p =p-p_e/1/2pV^2_e.

If you know the pipe diameter and you have the fluids velocity, the acceleration (and resulting drop in pressure is proportional to the pipe diameter. Even a mid section value could be examined like the question above and the values evaluated to see the change in diameter and resulting decrease in pressure and increase in velocity.

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&#Good responses. See my notes and let me know if you have questions. &#