There are a bunch of different ways to demonstrate shear thickening fluids (eg. Cornstarch in a paddling pool). However, some of these are a little messy. A tidier method is to use some silly putty. I can’t remember when I first saw this demonstration. I think it was in a chemistry class at UNSW when I was an undergraduate.
- A ball (or 2) of silly putty
- A tennis or squash racquet.
- Something to support the racquet so that you can see below it (for example, a glass tank).
The demonstration has 2 parts. In the first part you see the high viscosity behavior; in the second part the low viscosity behavior is shown.
Part 1: Roll the silly putty into a ball and bounce it on the racquet. This can be a bit of a challenge as it is hard to get the silly putty round enough to get it to bounce in a regular manner. You can also throw it at the wall and have it bounce back (though, again, it is hard to get a regular bounce. You may see it go off at an odd angle, so be careful not to hit anyone).
Part 2: Once you have finished various bouncing demonstrations mount the racquet with the strings facing up and place the silly putty ball on the strings. This part takes some patience. If you wait long enough, the silly putty will flow through the strings. It is best to do this at the start of class so that there has been some flowing by the end of the class.
Below are the before and after photos are shown below. The time gap between these two photos is several hours.
An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (firstname.lastname@example.org). I also welcome comments (through the comments section or via email) on improving the demonstrations.