is a beta 1.5c version of the CurveBall program, and you are invited
to participate in the beta testing. If you find errors in the program or
would like to suggest improvements, please send an e-mail to Thomas.J.Benson@nasa.gov.
CurveBall - Student
With this software 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. You can study aircraft wings with the
FoilSim III software available at this site.
There are several different versions of the CurveBall software that are now available, with
each succeeding version adding some additional factors that affect the flight of the ball.
This page contains the elementary student version and the only
acting on the ball is the aerodynamic
The motion is two dimensional and you can study the trajectory of the ball at the ballpark
and the flow of air around the ball in a wind tunnel at the same time.
This page contains detailed instructions on the use of the sliders and buttons in the program.
For experienced users, we have a
web page that contains only the software.
You can download the student version of the program to your computer
by clicking on this yellow button:
With the downloaded version, you can run the program off-line and do not
have to be connected to the Internet.
This version of the program includes the ability to change the size and weight of
the ball. Besides the default big league baseball, the code also includes
the characteristics of a fast pitch softball and a slow pitch softball.
Version 1.4b of the program is still available.
Version 1.4 only models a baseball.
After you have gained some experience with the student version of CurveBall, you
will want to try the
The expert version includes the effects of
on the flight of the ball. The resulting flight path is three dimensional, so you
must specify some additional parameters not found on the student version. You can
also view the results of the pitch from behind home plate.
There is a button on the page to download a copy of the expert version.
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
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 red Reset button at the upper right of the program.
If you see only a grey box at the top of this page, be sure that Java is
enabled in your browser. If Java is enabled, and you are using the Windows XP
operating system, you need to get a newer version of Java. Go to this link:
try the "Download It Now" button, and then select "Yes" when the download box from Sun
If you experience difficulties when using the sliders to change variables,
simply click away from the slider and then back to it.
the arrows on the end of the sliders disappear, click in the areas
where the left and right arrow images should appear, and they
The program screen is divided into three main parts:
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
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?
In the middle of the screen are the graphics windows.
The top graphics window shows the pitch
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.
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
The NASA Glenn Educational
Programs Office will continue to improve and update CurveBall based on user input.
Changes from previous versions of the program include:
On 9 May 12,
version 1.5c was released. This version includes the softball aerodynamics
and graphics, and the ability to input the ball weight and diameter. Versions
1.5a and 1.5b were development versions of the program and not released to the public.
The softball data used in the CurveBall computer program was
obtained by Peter Sherman, a high school student
from Seattle Washington, during a
shadowing session at NASA Glenn in 2012.
On 29 Oct 07,
version 1.4b was released. This version included the option to specify the
weather conditions and made some slight changes in the graphics.