Lab 13 (Fluid Drag) PDF

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Physics 151L Spring 2019: Lab #13: Fluid drag...

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Fluid Drag Objective: To measure the fluid drag coefficient of drag force and test if the drag coefficient is dependent upon the size of an object. Theory: Experimental setup:

Diagram 1: The experimental setup of the tube containing EP 68 oil used to measure the drag coefficient based off the velocities of various nylon balls.

Diagram 2: The free-body diagram of the forces acting upon the ball when dropped into the tube of oil. The objective of this experiment is to determine the fluid drag coefficient of drag force (Cd) and the corresponging Reynold’s number of the configuration. We also look to see if the drag coefficient depends on the size of an object. To do so we need to find the experimental viscosity of the oil (ηoil), the radius of the nylon balls, and the terminal speed (v). The ηoil is determined from the temperature of the experiment environment, which causes the oil to resist flowing. The speed of the ball (v) is calculated from the times recorded from dropping nylon balls of different diameters into a tube filled with EP 68 oil. The average time obtained from five

8 rg pball −1) . The ( 2 3 v poil experimental data obtained is also used to calculate Reynold’s number (R ) using the equation: pVd R= . The R values obtained will further be used to determine if the drag force acting η upon the ball; Interstitial drag if the R>1, and viscous drag if the R1.0). For the second ball R2, The R value determined that inertial drag was present in the system (19.85>1.0). For the third ball R3, The R value determined that inertial drag was present in the system (7.79>1.0). For the fourth ball R4, The R value determined that inertial drag was present in the system (2.28>1.0). For the first ball R5, The R value determined that inertial drag was present in the system (2.20>1.0). From our experiment the average terminal speed obtained was 8.85±δ1.26

Conclusion: We successfully fulfilled the objective of this experiment which was to determine the fluid drag coefficient of drag force (Cd) and the corresponding Reynold’s number of the configuration. We also look to see if the drag coefficient depends on the size of an object. From our calculations we are able to determine that the drag coefficient does depend on size, as the size of the ball decreased, the drag coefficient increased. Potential sources of systematic error are Instrumental. Instrumental error occurs when you drop the nylon balls into the oil, the oil coats the surface which causes it to stick to your hands when releasing it. This causes a delay when timing the later periods (3T, 4T, 5T). Another source of instrumental error potentially occurs occurs for the smaller nylon balls (R3, R4, R5) the oil coating the ball causes the ball to be

dropped at an angle which would increase the period since it is not travelling straight down. The source of error that is most likely occurring is the error occuring from the ball and the oil. Questions: 1. How well did your data agree with the experimental curve in Fig. 16.4? The data fit the experimental curve since the data points followed the linear curve between 1-102 R (see figure 1) 2. None of the measurements were in the region of viscous drag. 3. All of the measurements were in were in the region of inertial drag....