Shulou(Shulou.com)11/24 Report--

Original title: "Ink drop + boat = forever?" | serious play "

Is it the legendary curvature engine?

Is it an unknown mysterious magic force?

Or "perpetual motion machine"?

Wrong! Neither!

Today, the editor will show you.

Ink engine version of the boat is who is sacred.

Laboratory equipment ink refill (several), a piece of hard paper jam

The first step of the experiment is to cut the cardboard into the shape of a boat. (the shape of the cut can exert everyone's imagination, such as small boats, airplanes, robots, etc.)

Step 2: drop the ink on the tail of the boat so that the ink can touch the surface of the water for a while.

Tips: if everyone blows it out, be careful not to suck it into your mouth.

Step 3: slowly and vertically put the boat into the water and observe the movement of the boat.

Step 4: take out the refill and put it on top of the water.

Step 5: drop the ink inside the refill into the water and observe the change of the ink.

Is it like setting off fireworks?

It was originally understood that the ink is insoluble in water and will spread as soon as it comes into contact with water. The diffusion of ink will lead to an increase in the area of the water surface, as shown in the following figure. The expansion of the surface will bring a certain force to the ship, resulting in the movement of the ship.

Schematic diagram of surface force action

So where does the energy come from?

It's actually the energy of surface tension. Surface tension energy is the change brought about by each increase of unit area of the surface. When the ink area increases, the surface energy will be reduced into the kinetic energy of the boat.

So it's not some rumors on the Internet that there is a "perpetual motion machine" that doesn't need energy.

Reference:

Https://mp.weixin.qq.com/s/EupPvjhVDYHrl2q0QgHVaA

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Ah Yi & Xiao Pa & iu

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