How do you think we are going to propel this boat has no motor or no sailing?

Difficulty: Low

Materials :

  • Eva rubber of the color you want. You can find it in the Chinese bazaars.
  • Scissors
  • Pencil
  • Elongated and transparent container if possible. But you can use the aluminum trays that are used for cooking, they are the ones we have taken.
  • Soap cleaning dishes
  • Stick of the ears
  • Stick to move the ship

Steps to follow:

1.Draw a boat shaped arrow in the rubber eva and make a hole in the back so that it looks like this:



2.Cut the boat and put it in a bowl of water.

3.Put soap on a stick and touch the hole of the boat with the soap

You will see how the ship advances without engine or sail !!!

For the boat to work well, you must change the water often.


Create your own designs:

Now that you’ve seen how it works, I propose that you create your own designs and prove what shape and size works best.

For example, you can make a ship that does not have an arrow shape, or a very large one and a very small one, which one sails better? See if the shape of the ship is important.



Why does this happen?

The molecules of water attract each other with enough force.

By placing an object in the water, such as the little boat, the object is attracted by the water molecules that pull in all directions. This causes the ship to not move.



Soap serves to reduce the force with which the molecules attract .

If we put the soap in the container, all the molecules of the water lose strength but do not advance the boat. However, if we only put soap in the back, through the hole, the water molecules in the back lose strength but the rest will remain strong.

In this way, the front molecules have more strength than the rear ones and the ship advances.



Another way to explain it is through the Marangoni Effect

Marangoni Effect:

The Marangoni effect defines that a fluid will want to flow from areas of lower surface tension to areas of higher surface tension. Let us first explain what is and how surface tension.

Surface tension is a term that applies to liquids and measures how molecules interact with each other and attract. It is said that a liquid has more or less surface tension, depending on whether its molecules are more or less attracted to each other.

¿ What happens when two liquids of different surface tension (high/low) are?

In our experiment, we used soap and water, two liquids of different surface tension. Water has a high surface tension , while soap has a low surface tension . For each liquid there is a contractile force on the surface. But since water has a higher surface tension than soap, the contractile force on the surface is greater for water than for soap. The surface tension of the water will pull harder than the surface tension of the soap. Liquids with lower surface tension are attracted to liquids with higher surface tension.

Applied to our experiment, we see that when two liquids of different surface tension (water / soap) come into contact, a force is generated that produces movement from areas of lower surface tension to those of higher surface tension, and for this reason our ship Move on water.

The Marangoni effect shows us that a liquid with a low surface tension will tend to flow towards another with a higher surface tension, provided that both liquids are in contact. Thus, our BARC or advances because soap (less surface tension) is “pulled” from the water front (with higher surface tension).

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