is a beta 1.4c version of the SoccerNASA 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.
Many students enjoy playing and watching the game of soccer (which is known as
"football" in every country in the world except the United States).
With this software you can investigate how a kicked soccer ball
"bends" as it flies through the air.
A soccer ball encounters
as it flies and you can vary the
values of the factors
that affect the size of the forces on the ball.
These are the same forces that generate the lift
drag of an airplane wing and produce a
You can study aircraft wings with the
FoilSim III software and
the aerodynamics of baseball with the
CurveBall program available at this site.
The flight of a soccer ball is a fairly complex physics problem.
The flight path is described by integrating Netwon's
second law of motion.
The external forces on the ball are the
and the aerodynamic
The weight is constant, but the magnitude of the aerodynamic forces depend on the
which is a function of location and local weather conditions, and the
square of the
which changes during the flight.
The resulting flight path is three dimensional, so you
must specify several parameters to define the initial conditions when the ball is kicked.
This web page describes the variables required for the calculation
and how to set the values for the variables using the graphical user interface
for the computer program.
If you find that all of the input parameters are too confusing, we
recommend that you first try the
student version of the baseball curve ball simulation.
The student version only models the aerodynamic
side force acting on a ball.
The motion is two dimensional and the number of input parameters is
greatly reduced. After you acquire some experience, you can always return to this three
dimensional problem to study the kicked soccer ball.
This web page contains detailed instructions on the use of the sliders, boxes, and buttons
for the soccer ball program.
For very experienced users, we have a
web page that contains only the software and no instructions.
That web page loads a little faster than this one.
You can also download your own copy 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.
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
This program is designed to be interactive, so you have to work with the program.
There are a variety of input "widgets" that are used in the graphical user interface.
There are several colored buttons used by the program. To operate a button,
use the mouse to move the cursor over the button, and click the left mouse button.
At any time, to return to the original default conditions,
click the orange Reset button at the upper right of the program.
A choice box has a descriptive word displayed in a box with an arrow to
the right of the box. To make a choice, click on the arrow to display the choices,
move the cursor down the selection menu and click to
make your selection.
Some variable choices are made using round radio buttons. To make a choice,
move the cursor onto the round button and left click. A small black dot appears in the
chosen radio button.
Current values of the design variables are presented to you in text boxes .
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.
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
should reappear. These are known Java problems.
The program screen is divided into two main parts:
On the left side of the screen is the graphics window.
The graphics window has four possible displays: a downfield view, top view,
side view, and TV view. The TV view is a perspective view from the sidelines.
You choose your view by clicking on the appropriate box at the top of the graphic
and the current choice is by a yellow "light".
You can move the graphics side to side and up and down by moving your cursor
into the window, holding down the left button on the mouse and dragging
the graphic. You can "zoom" into the graphic by using the slider at the bottom
of the window. Click on the yellow vertical bar, hold down and drag the bar
from side to side. If you lose the picture, click on the "Find" button at the upper
right to restore the default graphics location and size.
Above the graphics window is a picture of a spinning soccer ball.
The spin axis of the ball is shown on the ball and you can adjust the
axis using the input devices described below.
By adjusting the spin axis, you can make the aerodynamic
cause the ball to bend, lift, or dive.
If the spin axis is vertical, the ball
curves from side to side, which soccer players call a "bend".
If the spin axis is horizontal, the ball lifts or dives depending on the
direction of the spin.
If the axis is between vertical and horizontal, you get a little bit of both effects.
You can see the effects of spin and gravity on the vertical flight path by choosing the
You can see the side to side effect on the horizontal side path by using the
You can see the combined effects of aerodynamics and weight in the
downfield view and the TV view. We have drawn the
goal and net in each of the view windows so that you can adjust the
input parameters to score a goal. For the corner kick, the objective is
not to score a goal, but to put the ball in front of the goal with sufficient height
so that a teammate can "head" the ball into the goal. So for the corner kick, a
blue target box will appear in front of the goal and your job is to get the ball into
the target box.
The input parameters for the kick are specified on the
right side of the screen.
Beginning at the top, we have four buttons that initiate the kick and control
The green "KICK" button begins the solution of Newton's equation
to determine the trajectory. When you click on the "KICK" button, the
boxes below the buttons display the time, speed, and magnitude of the
forces during the flight of the ball.
The blue "Save" button can be used to freeze the graphics of a completed kick for
comparison with a later kicks. The white "Clear" button erases all the graphics and
prepares you for the next kick. The orange "Reset" button can be used at any time to
return the program to its intial conditions.
Immediately below the colored buttons are some radio buttons to choose the type of
kick. For a penalty kick the ball is placed in the middle of the field,
36 feet from the goal line. You cannot change the location of the ball for a penalty kick.
You can change the angle at which the ball is kicked using the boxes and sliders at the
The vertical angle is the angle formed between the direction of the kick and the ground,
while the side angle is measured from the downstream (towards the goal line) direction.
For a free kick, the ball is initially placed 60 feet from the goal line and 30 feet
from the centerline of the goal. For a free kick, you can change the location using the input
boxes or sliders located at the bottom right. Y - side is measured from the centerline
of the goal, and X - distance is measured from the goal line.
For a corner kick the ball is placed in the corner formed by the sideline and the goal.
You can kick with either your right foot or your left foot
by clicking on the round radio buttons located below the type selection.
The direction of rotation is reversed between right foot and left foot.
The Spin Axis angle (degrees) and the Spin -rpm (revolutions per minute)
are set by using the input boxes and sliders at the lower right
listed under Kick Input.
As mentioned above, if the spin axis is
vertical (angle equals zero), the
is purely horizontal and the the ball moves left or right
depending on the direction of rotation. If the
axis is horizontal (angle equal to +/- 90 degrees),
the side force is vertical and lifts or dives the ball, depending on the
direction of rotation (+/- value of spin).
The amount of the force and flight trajectory also depend on the initial
speed of the ball. You set the speed using the box
and slider in the Kick Input.
Finally, the value of the side force depends on an efficiency factor called the
lift coefficient Cl. The default value for a spinning
soccer ball is .25. You can change the value of Cl as described below.
Besides the side force, there is an aerodyanmic
drag generated on the ball which opposes the motion.
The size of the force
depends on the square of the speed, the
density of the air and the value of the
drag coefficient - Cd. The default
of the drag coefficient for a soccer ball is about .25.
To allow you to study the effects of lift and drag
on the flight of the ball, you can select to input a lift and drag coefficient by
using the radio buttons at the upper right. Select "Input" and then
enter in the value in the input boxes
labeled Cd and Cl.
Below the flight data boxes are some choice buttons to select
the stadium location and the weather conditions.
Changing the stadium location changes the
atmospheric conditions because
the atmospheric conditions depend on altitude.
We have included all of the stadium locations used during the 2010 World Cup
so that you can study how altitude effects the flight of the ball.
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
and temperature change with
altitude. For the average day, we have the
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.
The Hot, Humid Day includes the effects of relative humidity.
The program calculates the air density
that corresponds to the temperature and pressure through the
equation of state.
The objective of the corner kick is to put the ball into the target box. The objective of the
penalty kick and free kick is to put the ball into the goal.
Try setting up a kick that scores a goal and then change the stadium location.
What happens to the trajectory? (In soccer, scoring is much harder than it looks!)
The NASA Glenn Educational
Programs Office will continue to improve and update SoccerNASA based on user input.
Changes from previous versions of the program include:
On 25 Aug 10,
version 1.4c was released. This version of SoccerNASA allows you to default
or input both lift and drag coefficients.
On 16 Aug 10,
version 1.4b was released. This is the first release version for SoccerNASA.
Earlier versions of SoccerNASA were developmental versions and not released to the public.