This post is part of a series of static electricity activities. Check out the whole series! For a brief discussion of static electricity basics, check out the first post.
Electrorheological is a fun word to say (here’s how to say it in a British accent) and a fun concept to play with! It describes liquids that change their viscosity – that’s how fast they flow – when they are in an electric field. Basically, electrorheological fluids stop flowing in the presence of static electricity.
To make an electrorheological fluid (have you said it yet? It’s fun!), just add 3-4 tablespoons of cornstarch to ¼ cup of vegetable oil. Stir it up well until the cornstarch is dissolved and you have a liquid the consistency of thin gravy.
Charge up the nearest balloon or Styrofoam cup by rubbing it on your hair (or the hair of the nearest child or pet).
Pour the cornstarch-oil gravy from one cup into another and then hold your charged cup near the flow of liquid. You liquid should stop flowing and you might even see solid looking chunks jump on to the cup just like in the video below.
How does it work?
When the cornstarch particles are in an electric field (caused by the charged up cup or balloon) they link up like a net that slows down the flow of the oil. As soon as you remove the electric field (balloon or cup), the oil flows as before.
Applications of electrorheological fluids can be found in electronics and your car. An electric field can be used to control the fluid in the clutch, brakes and even shock absorbers.
Questions to explore for fun or even for a science fair project
- Does it matter how much cornstarch you put in the oil? Try just 1 tablespoon or equal parts oil and cornstarch.
- Does it matter what type of oil you use? How about baby oil, mineral oil, olive oil, motor oil or anything else you might have.
- Do other liquids, like water, or other fine powders, like baking soda, do the same thing?