Streamline shaped with low air resistance

Let's take a look!

Let us experiment with a shape that reduces the force when the wind hits an object. Attach a pointed shape to the front side of a square bar and a round shape to the back side. First attempt to blow the wind in the direction of the pointed side in the front and then to the pointed side in the back.
When the wind is directed toward the pointed side in the front, the elongation of the rubber string is about 11 cm. Since it is about 32 cm when only the square bar is used (Force received from wind 2 (Effect of shape)), the force caused by the wind (air resistance) becomes small.
Next, if you put the pointed side to the back, the elongation of the rubber string is about 8 cm. The force caused by the wind (air resistance) becomes even smaller than that when the pointed side is in the front because vortex formation is prevented on the back side by the sharpening of the back. Such a shape with a round front side and a pointed back side is an ideal shape with low air resistance and is called a “streamlined shape.” The streamlined shape often used in practice is thinner than the shape used in this experiment, and therefore, the air resistance becomes even smaller.

[Development]	Drag F_D(such as air resistance, water resistance) can be expressed by the formula (Drag F_D) ＝ (Drag coefficient C_D) × (Fluid density ρ) × (Speed U )² × (Frontal projected area S) ÷ ２ Here, drag coefficient C_D is determined by the shape of the object. The drag coefficient of the wing (streamlined) used in airplanes, etc. is C_D= 0.04–0.1, and the drag is very small, which is ideal compared to that of other shapes.
[Keywords]	Air resistance, Drag
[Related items]	Function of wind and rubber, Force received from wind 2 (Effect of shape), Dolphin Jump
[Reference]	“The Wonders of Flow”, Japan Society of Mechanical Engineering, Kodansha Blue Backs, P148-155. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P54-55, P70-71, and P98.

Last Update：3.3.2023