Today I wanted to bring you a new experiment that we usually do at home, this time with water because that is what the arrival of the spring heat has: we don't care so much for soaking a little. But do not worry because there is little risk to form puddles in the kitchen or to get your clothes wet, therefore you have few excuses not to try it.
I have to tell you that The surface of the water when it is still forms a film because the molecules stick together forming a surface tension. And this activity consists in demonstrating first of all how this kind of "skin" acts, and then how an external agent (dishwasher) modifies this property. It's very easy, you only need a transparent glass bowl wider than deep (for example a baking tray or a bowl of salad), a little tap water, a handful of toothpicks and two drops of soap.
Procedure: First we fill the container and leave it on a stable surface until the water stops showing signs of movement. Then we take a number between five and seven toothpicks that we will leave very carefully on top of the water (we can help each other with these sticks) so that the tips are joined in the center.
With a little skill you will get to form a kind of star. When you have succeeded (do not worry because although the toothpicks are soaked it can work), you can use a thick empty syringe to take some detergent and you will pour one or two droplets in the center of the star.
The result is visible in a matter of seconds: quickly chopsticks separate and move towards the edges of the container, and it happens because as I said this external agent modifies the functioning of the surface molecules of water and it loses the "film" that covers it.
The kids love it, that's for sure, and you'll be surprised.
Images | Nikhil Verma on Flickr, screenshot of the video "Experiments with water" on the Expociencia channel. In Peques and More | Experiment to demonstrate the properties of hot and cold air
