Function of wind and rubber

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Let us conduct an experiment for verifying the “function of wind and rubber” that we learn in science in 3rd grade Elementary school.
• Rubber stretches when pulled strongly, and stretches slightly when pulled weakly. The greater the pulling force, the longer the rubber will stretch. Further, stretched rubber will attempt to return to its original form. This property of rubber can be used to move things.
• If you attach a rubber string to a model car, pull it and release it, the car will run as the rubber attempts to return to its original form.
• Wind can exert force on things or move things. A stylofoam square bar is attached to a model car tied with a rubber string. The wind is applied to this and experimented with the force of the wind. The thinner and longer the rubber string, the longer it stretches and the easier it becomes to understand the change. This time, for the rubber string of a model airplane, a thickness of about 1mm and a length of about 80 cm are used.
• When the wind is weak (weak wind), the rubber stretches to about 23 cm. When the wind is strong (strong wind), it stretches about 33 cm. You can see that the stronger the wind, the greater is the force it exerts on things.
• The force with which the wind pushes things backward is called “Air resistance,” and it works in the same way as when things move in the air.
• When the wind hits something, the pressure is high on the front side, and a vortex is created on the back side and the pressure becomes low. The force that pushes things backward (air resistance) works because of the difference in pressure between the front and back. The phenomenon of vortex forming on the rear side is called “separation,” which is the biggest cause of air resistance.
• Even with the flow of water, the force that pushes things backward acts, and it is said to be the resistance of water.

[Development]	The magnitude of force attributed to the wind has the property of being approximately proportional to the square of the wind speed. If you double the wind speed, the air resistance will be about 4 times (22 times), and if you triple the wind speed, the air resistance will be about 9 times (32 times). Resistance due to flow, such as air resistance and water resistance, is called “drag” and can be expressed by the formula. (Drag FD)＝(Drag coefficient CD )×(Fluid density ρ)×(Speed U)2×(Frontal projected area S)÷２ Here, the drag coefficient CDis determined by the shape of the object. The frontal projected area S represents the area of the figure when the object is viewed from the front.
[Keywords]	Air resistance, Drag
[Related items]	Yacht Car 1 (Tailwind)
[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 and P58-63.

Next　▶