Seem to "jump". What I mean by this, is the( illusion ?) that makes the ball accelerate the last few feet ?
I heard in today's YES telecast that the Yankees have worked very hard to increase Aroldis Chapman's "spin rate" on his 100+ fastball. Is this related to the "jump" phenomenon ?
Jump refers to "rise" in a fastball. Which also doesn't happen. Two forces are interacting with a 4 seam fastball on the way to the plate: gravity is pulling it to the ground, and backspin creates air turbulence that counteracts its drop.
In theory, with enough spin and velocity you could get a ball to rise. But it would require velocity and spin well beyond what any pitcher has achieved.
So when hitters say a fastball jumps, what they're seeing is the ball dropping less than their mind expects.
Reduction in velocity and the spin rate can cause a pressure differential on the ball's surface which will provide an upward force. This is what makes airplanes fly.