ITWire

U.S. physicist Alan Nathan and U.S. engineer Terry Bahill modeled the trajectories of baseballs. Their results appear in the April 2008 issue of the American Journal of Physics.

Baseballs that are popped up have large amount of backspin due to the ball hitting the top of the baseball bat, which causes them to move in unpredictable ways.

A normally hit baseball takes a pretty-straightforward parabolic path, say from the player’s swinging bat inside the batter’s box and up and out to the glove of the center fielder.

However, a pop-up hit almost straight up into the air, say, to the catcher contains a lot of backspin as it spins under the influence of air resistance.

Nathan and Bahill used computer simulations to model the various forces on the baseball and to model how a baseball player reacts when attempting to catch a pop-up.

They found that there is a distinct reason why players have difficulties catching popped up baseballs.

In fact, they showed why many players move back and forth many times (sometimes called a “to-and-fro dance”) while attempting to catch the ball. The path of the pop-up is influenced by the huge amount of topspin generated when the ball hits the top of the bat. Then, a “rotating sheath of air” is generated around the ball, which causes the ball to take almost unpredictable movements in the air.

According to the New Scientist article “Why pop-ups are hard to catch”:

“In the worst case for the fielder, a backspinning ball begins by flying forwards at a steep angle, before the backspin forces its path to vertical, and then eventually sends it looping back on itself. Once it reaches its apex and begins to drop, the spin will cause the ball to cross back over its upward path.” [New Scientist, April 12-18, 2008, page 16; also online “Why a baseball 'pop-up' is tricky to catch,” subscription required]

Whew! No wonder fielders have difficulties in catching pop-ups!

Find out a bit more about the results from spinning soccer balls and footballs on the next page.