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Step 2.

Using a ruler, measure the distance between the red ball of the probe and the center of the ball. How fast is the airstream moving around the ball at this distance?

Distance will vary depending on screen resolution - typical = 1/2 inch .
Speed of the airstream depends on speed of pitch - typical = 190 mph

Step 3.

By moving only the slider to the left of the Probe Gage move the probe above the ball and take five readings of distance and speed. Record these in the chart below. Repeat this for five readings below the ball.

Answers will vary. Samples are shown below:

Upper Distance (X)
Upper Speed (Y)

Lower Distance (X)

Lower Speed (Y)

5/8 in
161.0 mph
5/8 in
157.2 mph
3/4 in
132.9 mph
3/4 in
127.0 mph
7/8 in
118.5 mph
7/8 in
109.2 mph
1 in
103.6 mph
1 in
102.4 mph
1 1/8 in
79.9 mph
1 1/8 in
76.0 mph

Step 4.

Using two different colored pens, graph the information from the chart on the graph provided. Graph #1 will be above the ball, and graph #2 will be below the ball. Answers will vary, depending on the answers in Step 3.

Conclusions:

1. What happens to the airstream as the probe is moved farther from the center of the ball? The airspeed slows as the distance from the center of the ball increases.

2. Why do you think this happens? The ball disturbs the air locally, but it must return to free stream conditions far from the ball.

3. What happens if you change the speed of the ball? The local airspeed magnitude will change, but still decreases as the distance from the ball increases.

4. Does this change what you discovered in Question 1? No.

5. Does your result change if you put Spin on the ball? The local magnitudes will change top to bottom, but the airspeed still decreases with distance from the ball.

6. Examine your graphs. What kind of a relationship exists between an airstream's distance from the ball and the speed of the airstream? An air stream's distance from the ball and the speed of the air stream are an indirect variation. As the distance from the center of the ball increases, the airspeed increases.

7. Write an equation for one of your graphs. The graph represents a quadratic relationship. Therefore, the equation will be in the form ax2 + bx + c. Several methods can be used to develop the equation. Using a graphing calculator, the regression equation can be easily found. It will be similar to 1.25x2 - 43.48x + 549.36, allowing for differences in recording data.

8. Why is this the correct equation? It is a quadratic equation that best fits the experimental data.

Related Pages:
Standards
Activity
Worksheet
Lesson Index
Aerodynamics Index

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