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Hit Modeler Interactive Simulator

Aerodynamic Forces

With this simulator you can investigate how a baseball flies through the air by changing the values of the factors that affect the aerodynamic forces on the ball. These are the same forces that generate the drag of an aircraft wing. The flight trajectory is determined by the initial velocity and the relative size of the drag and weight of the ball. We provide a page of results which you can use to check your calculations.

You can select a baseball, a softball, or any ball that you describe by giving the diameter, weight and drag coefficient. The motion is two dimensional and you can study the trajectory of the ball at the ballpark of your choice, and with selected weather conditions. This page contains detailed instructions on the use of the sliders and buttons in the program.

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.

General Instructions

This program is designed to be interactive, so you have to work with the program. There are a variety of choices which 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 white box with black numbers is an input box and you can change the value of the number. A black box with yellow 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 orange Reset button at the lower left 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 is the graphics window. The graphics window shows the trajectory of the hit ball. The simulation is two dimensional and you are looking parallel to the ground. Weight and aerodynamic drag are the only forces acting on the ball. Along the top of the window, the height and distance from the plate are updated during the flight. There is a wall set at 350 feet from home plate.
  2. At the lower left of the screen are input choices concerned with the stadium location and the weather. 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 drag on the ball. At any time you can return to the default conditions by pushing the orange Reset button.
  3. At the lower right of the screen are input choices concerned with hitting the ball. There is a menu to choose a baseball, softball, or input a ball design. To set up for a hit, you must specify the speed and the angle at which the ball leaves the bat. The angle is measured relative to vertical; 0 degrees is straight up, 90 degrees is along the ground. A small arrow on the ball in the graphics window will help you determine these values. If you select baseball or softball, then the drag coefficient, weight, and diameter of the ball are set by the program. If you select “input Ball”, you can vary the drag coefficient, weight and diameter of the ball by using the appropriate box and slider. The default value of drag coefficient is .3, which has been determined experimentally for a major league baseball at about 100 mph. By setting the value to 0.0, you can remove drag from the calculations and see the large effect that drag has on the flight of a baseball. You can also vary the strength and direction of the wind. When you have your conditions set, click on the red SWING button to launch the ball into the air. You can save your flight trajectory to compare with a new set of conditions by pushing the blue Save button. And you can clear all of the graphics by pushing the white Clear button.

Have fun!

Learn more about the aerodynamics of baseball.

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