Let's examine how the speed at which a baseball is thrown relates to the speed of the air flowing around the surface of the ball. To begin, choose Speed at Surface on the Plotter Control Panel and choose Cleveland (sea level) on the Baseball Input Panel.
Now we need to set the conditions for our first pitch. We want to start by throwing a FASTBALL. This should already be set with the SPIN slider centered on Fastball and the SPIN value reading 0. If not, click on the word Fastball.
Since we have the ability to throw some serious heat, begin moving the Speed slider slowly to the right toward 100 mph. On the view of the ball (which is a top view), notice that the green airstream to the right of the ball and the yellow airstream to the left of the ball start moving faster as the ball speeds up.
One change that is very obvious is that the curve on the Plotter View Panel grows higher and higher as you move the Speed slider. This shows that the ball is pitched faster. The air at the surface of the ball moves around the ball faster relative to the air that is a little farther from the ball that is going in the same direction.
Also, a less obvious thing to note is that there is only a yellow curve in the Plotter View Panel which shows the speed of the air going around the left side of the ball. What about the air going around the right side of the ball? Where is the green curve for the green air? Why only one curve? The answer is that the green curve is there, but it is exactly under the yellow curve! In other words, the speeds of the airstreams on both sides of the ball are identical. This is an important point for later in our discussion.
Now move the Speed slider all the way to the left (very slowly!). At the bottom of the Baseball Input Panel is a readout for the SIDE FORCE, a force that would act to push the baseball left or right (curve). Write down the value when the speed is 35 mph. Now move the Speed slider to a position near 50 mph and again record the SIDE FORCE reading. Finally move to 100 mph and again record the SIDE FORCE on the ball.
For all speeds the side force is zero. The speed was identical on both sides of the ball.
To verify your prediction, click on the Ballpark button on the Plotter Control Panel. Now click back to Speed at Surface.
With the Speed slider at 100 mph, look again at the graph in the Plotter View Panel.
The air moves faster the farther its path is changed. The air stream exactly in front of the ball slows down as it approaches the ball and stagnates as it hits the front of the ball. As it is deflected out of its path by the shape of the ball, it moves faster and faster, reaching a maximum midway around the ball at the point of its farthest deflection. Then it starts to slow again until it reaches the rear of the ball, where it is back to its original path and back to the same speed as the rest of the nearby air.
It's time for the next Lesson -
Pressure and the Curveball
Or
go back to Baseball Lessons