Table of Contents:
Background Information Statement of the Problem Hypothesis Procedures Data Uncertainty Conclusion Table of Contents Summaries of Related Sources Return To Research
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Wind tunnels are used for transportation, such as planes and roadway traffic, and any experiment that uses wind as a variable, like hurricane simulations. A way to control a wind is through a funnel rather than a tunnel. This method is called the Venturi Effect, which is where the Bernoulli's principle is used in a funnel. Bernoulli's principle is that "the total energy in a steadily flowing fluid system is a constant along the flow path. An increase in the fluid's speed must therefore be matched by a decrease in its pressure" (Landis). Pressure is the amount of force inflicted on a certain area. This infers that the force of the wind should also decrease. The experiment also calls for a string and with that a centripetal force, I can determine that the force will equal the mass multiplied by the velocity squared divided by the length of the string.
Statement of the Problem: Table of Contents
The purpose of this experiment is to find how the width at the end of the wind funnel affects the velocity of the wind and the force it has on a ball when strung from a ceiling.
Review of Literature:
Hypothesis: Table of Contents
All of this information leads me to hypothesize that the force on the ball will decrease linearly. This is because the decrease in width of the funnel leads to an increase in velocity of the wind, which leads to a decrease in the pressure, that the wind will have on the ball. The equation for force is pressure multiplied by the area. Seeing as the area of the object stays the same and the pressure should decrease due to Bernoulli's effect, the force should also decrease.
Procedures: You need: a fan, something shaped like a funnel with one end wider than the fan; straws that fill the funnel (to make sure the air flows straight and consistently), felt or another material to cut different sized holes in
1. With the felt- cut at least four different sizes of holes that are all smaller than the original hole at the end funnel using separate pieces for each hole
2. Construct the wind tunnel by filling the funnel with straws that are all facing straight outwards and then attaching the funnel part to the fan
3. Tie a lightweight ball to a string (a small bouncy ball works great)
4. Place the fan so that (1) it is directly behind the hanging ball, (2) it can be easily plugged in if applicable, and (3) there is space in front of the ball and (4) a wall is on one side of the contraption
5. Either tape a meter stick perpendicular to the funnel and parallel to the ground or have a pencil to mark where the ball reaches
6. Without a hole modifier, turn the fan on- wait for about the fifth push to ensure proper air movement and measure how far away it is
7. Repeat step 6 at least two more times
8. Repeat steps 6 and 7 with all of the different sized holes
9. Graph and Compare the data!!
Data: Table of Contents
In the graph, the black x's are the actual data points and the purple dots are the average distance in centimeters that each radius (also in centimeters) obtained.
Radius of exit 1cm 1.625cm 3cm 3.95cm 6
Trial 1 11.75cm 11.43cm 17.15cm 15.88cm 9.84cm
Trial 2 9.84cm 12.38cm 16.51cm 13.97cm 7.62cm
Trial 3 8.41cm 12.7cm 17.46cm 15.24cm 6.99cm
Trial 4 9.53cm 11.75cm 16.83cm 14.92cm 6.99cm
Trial 5 9.21cm 12.07cm 17.15cm 15.88cm 8.26cm
Average distance 9.748cm 12.066cm 17.02cm 15.178cm 7.94cm
Conclusion: Table of Contents
Rather than a linear decrease, this experiment produced an exponential curve. The explanation for this is that as the hole gets larger more air is passed through and so there is more force on the ball but there is a brink point when more air would only be a deterrent. This probably occurs when the hole becomes larger than the ball because at that point the air would be both inflicting a force on the ball but also acting as friction against the ball because the excess air just goes around the ball and could not apply a positive force causing the possible distance to decrease. There were a few errors in this experiment. The most important error was accuracy in the data. Because the ball was tied to a string there would have been a slight vertical change in distance. However, the vertical change was so slight that it was not realistically calculatable. Also, the contraption was not in an enclosed location and so the ball was not ensured to go straight. Were I to do this experiment again, I would use a more portable wind funnel so that I could measure a rolling ball, which would decrease the number of uncertainties in the experiment.
Summaries of Related Sources:
This site looks at one of the earlier wind tunnel experimentation. The experiment was how the density of the air would affect the tunnel. This resulted in the Langley Laboratory's Variable Density Tunnel. Pictures of this are included in the site.
This site is a summary on the different types of wind tunnels referring to both the variables within the wind and variables with the tunnel
This site looks briefly at how wind tunnels work, a few types of wind tunnels, and a history of the wind tunnels.
This site tells one everything that they could wish to know about the Oran W. Nicks Low Speed Wind Tunnel including general information, information about the facilities, and some pictures of past uses of the wind tunnel.
This site is a more in depth history of the original wind tunnels.