Did You Know?
Does the ball really travel further in hot, humid air?
Does the ball really travel further in hot, humid air?
Yes, a baseball actually does travel farther in hot, humid weather. When the air feels “heavy” with moisture, it is actually “lighter”.
Hot, humid air is less dense than cold, dry air, so a baseball that might not make it out of the park when hit on a cool day may have just enough “legs” on a hot, humid one to clear the fence.
Ref: Rainbows, Curveballs, and Other Wonders of the Natural World Explained, pg 91. Ira Flatow
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Does a Curveball Really Curve?
A fast ball is not the most difficult pitch to hit. Lots of players make a living hitting a good, major league fastball. The pitches that give most batters a problem are breaking pitching: curves, sliders, and split-fingered fast balls. Baseball veterans often say they knew they had to retire from the game when they couldn’t hit the curve ball anymore. These baseballs don’t overpower batters like blazing fast balls; they hamstring players who helplessly watch them dance across the plate—hooking, tailing, dropping, and twisting in such unbelievable ways that some batters are convinced the sharp drop of a curve ball is really an optical illusion or the result of the illegal use of sandpaper to scuff up the ball. Batters would like to believe that no human being could be talented enough to cause a leather-covered, five-ounce sphere to follow such an erratic course. “It just isn’t natural”.
The curve-ball controversy has been debated so intensely that in 1941, Life and Look magazines took stop-action photographs of curve balls to determine if the baseballs really did curve. Life concluded: “evidence fails to show the existence of a curve,” while Look discovered the opposite: the ball does curve.
Even as recently as 1982, Science magazine commissioned scientists at General Motors and MIT to conduct a modern scientific investigation into the question. Once again stop-action photography was employed to show that a curve ball’s curve is not an optical illusion but is based upon sound laws of physics.
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Snapping Your Fingers
The secret of the curve all is not its velocity (important to the fast ball), but its spin. Throwing a curve ball is a lot like twisting a doorknob or snapping your fingers. A sharp twist of the wrist puts a fast, forward spin on the ball. Like the dimples on a golf ball, the stitches on the baseball (all 216 of them), drag a thin layer of air around the ball.
Topspin of a curve ball causes air pressure on the bottom of the ball to be less than air pressure on top, so the ball sinks. This topspin causes air to flow faster along the bottom of the ball than along the top. The faster-flowing bottom air is stretched thin, causing greater air pressure at the top of the ball and forcing the ball down. The curving force can move the ball down a foot or more in flight. If there were no gravity, the curve ball would form a circle two thousand feet in diameter. But, after all, the ball is moving on our planet and not in outer space. So gravity affects the path of the ball, too, pulling the ball toward the ground.
The force of gravity is a continuously accelerating force. It makes objects move faster and faster over time. So the effect of gravity is most pronounced in the second half of the ball’s half-second flight to home plate. Combined with the curving force, gravity makes an overhand curve ball appear to drop suddenly, as if it had “rolled off a table” when in actuality the ball has followed a smooth arc during its entire flight. So when batters say it appears that the ball makes a sharp break right in front of the plate, they are partially right. And when scientists say the ball follows a smooth, circular path all the while, they’re correct, too. A pitch that takes less than half a second to reach the batter drops only half a foot due to gravity in the first half of flight, but in the second half it drops more than two feet. It that a sharp break? If you’re a batter, you think so. If you’re a scientist, heck, no, but you’ve never had a face former curve-ball ace Sandy Koufax.
Trivia:
Bottom (reverse) spin causes a fast ball to rise or “hop”. Because the ball is spinning toward the pitcher, a fast ball’s lower surface will be moving against the wind, creating greater pressure underneath the ball than above it, so the ball rises.
A “perfect” curve ball travels about a hundred feet per second, spinning at thirty revolutions per second.
Ref: Rainbows Curve Balls. An Other Wonders of the Natural World Explained, by Ira Flatow
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What Makes a Curveball Curve?
The speed of the air moving past the ball's surface is the trick to a curveball. As the ball spins, its top surface moves in the same direction in which the air moves. At the bottom of the ball, the ball's surface and the air move in opposite directions. So the velocity of the air relative to that of the ball's surface is larger on the bottom of the ball.
The higher velocity difference puts more stress on the air flowing around the bottom of the ball. That stress makes air flowing around the ball break away from the ball's surface sooner. The air then travels at the top of the spinning ball, subject to less stress due to the lower velocity difference, can hang onto the ball's surface longer before breaking away.
When a pitcher releases a curveball, the pitchers grip will put a spin on the ball. As the ball moves through the air it experiences a force called drag or air resistance.
If the ball isn’t rotating the drag will only make it go slower. For a baseball, when it is rotating, the force of the drag is different at different points of its path. The air friction is less on one side of the ball and because of that the ball tends to curve.
Something else that helps a baseball to rotate or spin is the roughness of the ball. If the stitches on the baseball weren’t on the ball the ball would be really smooth. If that were the case any of the special pitches such as the curveball wouldn’t be possible. For every action there is an equal and opposite reaction. So, as the spinning ball throws the air down, the air pushes the ball up in response. A ball thrown with backspin will get a little bit of lift.
"A major league curveball can veer as much as 171/2 inches from a straight line by the time it crosses the plate. Over the course of a pitch, the deflection from a straight line increases with distance from the pitcher. So curveballs do most of their curving in the last quarter of their trip. Considering that it takes less time for the ball to travel those last 15 feet (about 1/6 of a second) than it takes for the batter to swing the bat (about 1/5 of a second), hitters must begin their swings before the ball has started to show much curve. No wonder curveballs are so hard to hit."
Ref: (The Science of Baseball )
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