This is some cool science in a video that explains how you can take advantage of something known as “The Magnus Effect” with the application of just a bit of angular momentum, something baseball pitchers have known about for years
From the video comments: The biggest misconception about the Magnus Effect is that it is just a consequence of Bernoulli’s principle. It’s not. This can be demonstrated by varying the surface roughness of the ball. Smooth balls can actually curve in the opposite direction due to the ‘reverse Magnus effect’ because flow over one side is laminar while the other is turbulent. This is a great reference on the shortcomings of Bernoulli’s principle explanations: http://math.mit.edu/~bush/wordpress/wp-content/uploads/2013/11/Beautiful-Game-2013.pdf
Watch:
h/t to Harold Ambler
When I studied the Bernoulli Principle in Physical Chemistry class, I was impressed by the *assumptions* inherent in the derivation of the equation: (1) the gas is assumed to be confined to a tube of finite cross-section, (2) the flow of the gas is always laminar, (3) the gas has negligible viscosity, and (4) the texture of the surface is irrelevant. These assumptions are (1) mutually incompatible, and (2) only approximately realized at low pressure and low flow rates for ideal gases.
I realized immediately that the application of Bernoulli’s Principle to airfoils violates *all* of the assumptions, and therefore amounts to ‘smoke-and-mirrors’. I looked around and the only phenomenon I could find that made sense in context is the Coanda Effect. The Coanda Effect and the Magnus Effect seems to be closely related.
They both involve separation/attachment of boundary layers so the effects are related. The reverse Magnus effect is observed under laminar flow conditions. The Coanda effect is caused by the attachment of a fluid jet to a curved surface and consequent deflection downstream. Surface effects due to the surface roughness involve the difference between the laminar and turbulent boundary layers.
Any thoughts on Bush’s experiment with the smooth beach-type ball, reverse Magnus effect, and everyman’s observation of the behavior of smooth ping-pong balls?
Depends what you want to know, in the case of smooth balls it’s possible to get the case where the boundary layer on one side of the ball is laminar and on the other is turbulent. As a result the normal differential separation of the boundary layers is changed giving rise to the reverse Magnus effect. Interesting effects arise when the ball is accelerating or decelerating as the trajectory can start with a normal Magnus effect due to both sides being turbulent (or laminar), passing through a transitional phase when one side changes and so the reverse Magnus effect occurs, and then reverting to both sides being laminar (or turbulent) when the normal Magnus effect occurs. Light balls such as ping-pong balls deviate much more noticeably. Surface roughness can induce a variety of effects e.g. the effects of seams on the trajectory of cricket balls and baseballs.