AERODYNAMICS

 

A very simple wind tunnel using a plastic sheet rolled into

a cone. It blows air at 4 m/s onto a polystyrene ball supported

by two cotton threads (to reduce sideways motion). The angle

from the vertical measures the drag force.

 

 

Measuring the drag force on a balloon.

The forces on the balloon include gravity,

the buoyant force and the drag force.

 

 

Magnus force on a spinning balloon.

Clockwise spin     Counter CW spin     At 300 fps

 

Magnus force on a paper cylinder

 

 

 

Magnus force on two plastic cups taped end to end and launched with

backspin using two rubber bands. The result is a typical baseball “pop-up”.

Here is the method and here is a backspin “golf shot” at lower spin.

 

 

 

Slow motion 300 fps movie showing a 10 gram polystyrene

ball thrown with a home-made Lacrosse type launcher at

23 m/s with backspin at 2000 rpm. Defies gravity !

 

 

The same 10 gram ball launched with sidespin shows an equally dramatic

effect in the horizontal direction due to the horizontal Magnus force.

The spin axis is slightly tilted. The small vertical component of the Magnus

force counters gravity, so the ball moves in a horizontal plane.

 

Another example.     Even more surprising is Negative Magnus on a smooth ball.

 

 

 

 

 

 

Reverse swing of a cricket ball occurs at ball speeds around 90 mph,

provided the seam is aligned at around 20-30 degrees to the path of

the ball.  It can be easily demonstrated with a balloon at 1 mph.