To keep you amused over the Christmas and New Year break, we've compiled a short list of fun materials - stuff that behaves a little bit outside the norm. Here's what we came up with. 字串9
1. Dilatants - fluids that get more solid when stressed. The classic example is a mixture of cornflour and water - it's runny until you hit it when it becomes solid.
This video shows how that it possible to run across an apparently liquid pool of the stuff because your footfalls solidify it. If you stop, you sink.
I like this video better though - it shows how sound waves from a subwoofer produce interesting shapes in a dilatant. If you want to have a go yourself, try this recipe.
2. Auxetic materials - materials that get thicker when stretched. Pull them in one direction and they expand in another.
This video (.mov format) from Bolton University, UK, shows an auxetic foam in action. I like these because they are totally counter-intuitive - you just expect things to get thinner when stretched. Read more about them in a feature here or on this research page.
3. Superfluids - liquids that flow without friction. They can effortlessly flow through the tiniest of cracks and will even flow up the walls of a beaker and out the top. It's possible because all the atoms in a superfluid are in the same quantum state, so they all have the same momentum and move together. To make a superfluid you must cool helium down to a couple of a degrees below zero - not one to try at home. They can be used to make super-sensitive gyroscopes to test theories about gravity.
Sadly I couldn't find any spectacular videos of supefluids in action. Here's a not-too-exciting one of superfluid helium drops (mpg format). Read more here.
4. Ferrofluids - magnetic fluids that can look spectacular. They're made from nanoscale magnetic particles suspended in a liquid. The spectacular sculpture in the video below is made using a ferrofluid and electromagnets.
Ferrofluids can be used to drive speakers or make shock absorbers that vary their stiffness in milliseconds. This guide shows you how to make your own ferrofluid at home. 字串6
5. Dry ice. Carbon dioxide freezes at -78.5 °C and it's fun and versatile stuff. These videos show how it can produce massive amounts of bubbles when mixed with soap and water, drive a simple cannon , transform your swimming pool, produce pretty patterns when dropped onto water in small chunks and spice up the all-too-familiar Diet Coke and Mentoes reaction. You can even freeze soap bubbles hard and pick them up, if you follow this guide. A block of dry ic过敏性鼻炎用什么药治