The other day, I was reading in some old science book about flight. I came
across an example I was a little confused with. The example was how a spinning
ball was able to generate "lift" by giving it a backspin, in which I have
observed while playing volleyball or basketball. They authors gave an
explanation that it was due to the relative velocity of the top of the ball in
respect to the bottom of the ball.
I understand that as the velocity of air increases, the pressure decreases,
which ultimately leads to "lift". If a ball is thrown with no spin, the
relative velocity of the air on top of the ball is the same as the bottom of the
ball (Right now, I'm neglecting vortexes that form around the ball). If a ball
has a backspin, isn't the bottom of the ball have a higher relative velocity to
the air? The way I picture it, it would be like someone in a car traveling
50mph and throwing a ball 30mph ahead of him (with respect to the driver). The
relative velocity of the ball to a "stationary" person would be 80mph.
Since the bottom of the ball is spinning into the wind, wouldn't it have a
higher relative velocity in comparison to the top of the ball? I'm just curious
how does a backspinning ball "float" while a forward spinning ball "dives".