Find two identical drinking straws.Fill two glasses with some fresh water. Mix a squirt of dish soap into one of the glasses.
- Using both hands, lower the two straws into the two glasses at the same time.
- Next, covering the top openings with your thumbs, lift the two straws out of the glass and watch what happens.
- You will notice that the straw that was placed in the soapy water has smaller droplets of water that drip off of it while the straw in the plain water makes larger drops.
Scientific Principle at Work
Dynamic surface tension measures the attraction or “strength” between molecules in the liquid. The surface tension governs how much weight a drop of water can hold before it is too heavy and falls off the straw. Reducing the surface tension by adding soap means only smaller drops of water can form before falling off.