04.26.2017
Written By: Catherine Clark
The viscosity of fluids was the topic of study today at AIMs! First, we learned about why viscosity is important in our daily lives, and how the magnitude of viscosity can change by several orders of magnitude across substances we deal with every day (e.g. air and honey). Then we discussed the famous “resin drop experiment” in which a substance with a viscosity ~230 billion times higher than water has only released 9 drops since 1930. This raised the question of how one can actually distinguish between a solid and a liquid – something that still intrigues materials scientists today. We also learned the difference between a netwonian and a non-newtonian fluid, with “oobleck” as a classic example of a non-newtonian fluid. This made the students further question the distinction between solids and liquids.
To test what we learned, the students performed three experiments/activities. The first was a laminar flow experiment, where they put colored drops of soap in between two glasses, and turned the inner glass slowly. While the colors appeared to mix together, if the inner glass was carefully turned backwards, they would separate into their original colors. Students could explore how different viscosities impacted how easy it was to regain the original colors. In addition to this experiment, we also made lava lamps using oil, water + food coloring, and alka-seltzer tablets! This demonstrated the idea that viscosity and density are not the same thing, as oil is more viscous but less dense than water. Finally, we made oobleck out of corn starch and water, and the students had a ton of fun pushing on it at different rates to see how it would respond. This was a great activity that allowed us to explore how some materials can have viscosity responses that are qualitatively very different than common fluids like water and air.