Let's take a look!
What type of experiment is this?
Experimental procedure and explanation:
- Build a boat out of a thin styrofoam board. Float the boat on water and then pour a small amount of a neutral detergent behind the boat. When the neutral detergent spreads in the water, the boat will move forward. The same can be achieved using a solid soap or camphor (an insect repellent used for clothing) rather than a neutral detergent. In the past, camphor was used to create what is known as a camphor boat.
- This movement of the boat is due to the action of the surface tension of water. This surface tension is due to a mutually attractive force (cohesive force) between the molecules of water and other liquids. When water is spilled in the air in the space station, the water forms spheres. This is also because of the surface tension. Through the cohesive force, the molecules try to gather together to form a single mass.
- This type of cohesive force works in the same manner as the film tension (tensile force) that occurs when the rubber membrane of a balloon or the film of a soap bubble is stretched. Therefore, it may be easier to understand this concept if you think of it as a thin rubber film being spread out over the water surface. This is why the force is known as surface tension.
- Neutral detergents, soap, camphor, and the like are referred to as surfactants, because they reduce the surface tension.
- In the experiment shown in the video, when neutral detergent flows behind the boat, the surface tension of the water in that location is weakened. Conversely, water in locations that are not contacted by the neutral detergent maintains a surface tension that is larger than the surface where contact is made. As a result, a large surface tension is maintained at the front and sides of the boat, whereas the surface tension near the rear is weakened. A phenomenon that is like a tug of war then occurs with the surface tension, and the boat is pulled in the forward direction toward the region with strong surface tension.
|[Related items]||Three One-Yen Coins|
|[Reference]||Logergist “Physics Promenade (1964) (Zoku Butsuri no Sanpochimi),” Iwanami Shoten, pp. 58–66.
(Logergist is a name given to a group of seven physicists including Professor Isao Imai, and in the five volumes of “Physics Promenade” various physical phenomenon and daily events are considered.)
The Japan Society of Mechanical Engineers, “The Wonders of Flow (Nagare no Fushigi),” Kodansha Blue Backs, pp. 62–67.
Ryozo Ishiwata, “Illustrated Fluid Dynamics Trivia
(Zukai Zatsugaku Ryutai Rikigaku),” Natsume Publishing, pp. 48–49.