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Curve Ball Pitch Interactive

With this simulation you can investigate how a big league pitcher throws a curveball by changing the values of the factors that affect the aerodynamic forces on the ball. These are the same forces that generate the lift of an aircraft wing.

General Instructions

This program is designed to be interactive. There are a variety of choices that you must make regarding the analysis and the display of results by using a choice box. A choice box has a descriptive word displayed and an arrow at the right of the box. To make a choice, click on the arrow, hold down and drag to make your selection. The current values of the design variables are presented to you in boxes. By convention, a light box with dark numbers is an input box and you can change the value of the number. A dark box with light numbers is an output box and the value is computed by the program. To change the value in an input box, select the box by moving the cursor into the box and clicking the mouse, then backspace over the old number, enter a new number, then hit the Enter key on your keyboard. You must hit Enter to send the new value to the program. For most input variables you can also use a slider located next to the input box. Click on the slider bar, hold down and drag the slider bar to change values, or you can click on the arrows at either end of the slider. At any time, to return to the original default conditions, click the red Reset button at the upper right of the program.

If you experience difficulties when using the sliders to change variables, simply click away from the slider and then back to it. If the arrows on the end of the sliders disappear, click in the areas where the left and right arrow images should appear, and they should reappear.

Screen Layout

The program screen is divided into three main parts:

  1. At the top of the screen are input choices concerned with the type of pitcher, the stadium location and the weather. You can use the choice button next to the word “Ball” to select a baseball, slow pitch softball, fast pitch softball, or to input the ball information. For the first three selections, the black and yellow boxes will show the weight and diameter of the ball. For the input case, the boxes change to black on white and you enter the value of weight (in ounces) and diameter (in inches). You can be a right hander or a lefty by clicking on the round buttons on the left. If you push the blue button marked Set Up Next Pitch you will not see where the ball will go until you push the red Throw the Pitch button. Otherwise, as you change inputs, you will see the pitch trajectory in the graphics window. On the right, you can vary the stadium location and the atmospheric conditions at that location. You select the stadium location by using the choice button. The default weather conditions are an Average Day at the selected stadium. The average is based on an NASA model of the atmosphere and how the pressure and temperature change with altitude. For the average day, we have the temperature set to 59 degrees at each stadium. A Hot Day sets the temperature to 89 degrees, and a Cold Day sets the temperature to 35 degrees. You can change all of the atmospheric conditions by using the Specify option on the choice button. You can change the temperature, the atmospheric pressure, and the relative humidity of the air; the program will calculate the air density that affects the side force. Try setting up a pitch and changing the location. What happens to the trajectory?
  2. In the middle of the screen are the graphics windows. The top graphics window shows the pitch trajectory while the lower graphics window shows the flow of air around the ball. In both cases you are looking down onto the ball or the infield. The simulation is two dimensional with the ball spinning about an axis pointing into the Earth (or Mars). The force occurs side to side; we have not modeled the ball falling towards the surface. On the upper trajectory graphics window your pitch is judged as a ball or a strike. This window also tells you how far from the center of the plate the pitch first crossed the front of the plate. On the lower graphics window, you are moving with the ball, so the air appears to move by you from left to right. There is an aerodynamic probe which can be used to study the flow around the ball.
  3. At the bottom of the screen are control inputs for the aerodynamic probe and input choices concerned with throwing a pitch. On the left, a choice box is used to select what variable is being computed by the probe. The value of the variable is shown on the gage at the right. You move the probe by using the sliders located around the gage. A black output box also shows the magnitude of the side force on the baseball. On the right are inputs to set up and throw the pitch. To set up a pitch, you must specify the speed and the spin on the ball, the point on the pitcher’s mound from which you release the ball, and the angle at which you release the ball. A small arrow on the ball in the graphics window will help you determine these values. And the red stitches on the ball shows the direction and rate of spin.

Have fun!

Play Ball!

Please note: the simulation below is best viewed on a desktop computer. It may take a few minutes for the simulation to load.

Learn more about the aerodynamics of baseball.

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