the spin ……

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The basics

Before you brace yourself for the science, let’s get just one vital term straight.
Imagine that the Earth is a cricket ball, and that the seam is the Equator.
Then imagine a line straight through the ball going in at the north pole and out at the south pole. When the ball is spun around its seam by a spinner, this line through the ball is the axis around which the ball rotates, and has a rather unoriginal name: theAxis of Rotation.

I’ll mainly deal with the axis of rotation in terms of what it means for the aerodynamic forces on the ball, but there’s one important thing I ought to make clear:
When a body is spinning it is subject to gyroscopic effects that require a large force to change it’s rotational axis.
The practical upshot of this is that the axis of rotation of a spinning ball as it leaves the hand will remain virtually unchanged until the ball pitches.
I have sometimes observed that on TV a spinner’s delivery appears to change its axis of rotation in flight, and after much head-scratching I’m pretty sure this is an optical illusion caused by the strobe effect of the camera, as I’ve never observed this effect with my own eyes.

imagine a golf ball contentedly sat on its tee.
Golfers have learnt over the years that they need to slice underneath the poor defenceless little ball as they tee off, so that the ball travels towards the hole with the underside moving towards the hole and the top side moving away.
They do this because when a ball travels trough the air and spins around an axis of rotation that is
a) horizontal, and
b) perpendicular to its direction of motion, the air around the ball will push it upwards.
This means the ball will take off as it leaves the tee, allowing the golfer to hit the ball further.
a golfer hitting a backspin intends to use the force of the Magnus effect in one direction – upwards.

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