Science Buddies: "Ask an Expert"

Hi, on Mythbusters on TV they showed how if you put your hand slowly into a bucket of custard it will easily go up to your elbow but if you slap it with your hand the surface tension increases and it wont go in. you can even run across a pool of custard slapping your feet and not sink but if you stop still you will sink. Also on TV i saw a new material like placticine. you can squash it flat slowly but if you hit it with a hamer fast it stays the same shape and does not deform. what is this quality called, what causes it and how many polymers with these type of physical qualities are known and what are their names?
how can something lioquid or plastic have a quality of a solid when energy is applied. are the laws of thermodynamics in play here where if you add energy to a system the amount of entrophy decreases or is it something else.is there any resourse on the net i can read up on this that can help ?

Hi tristan512!

A clarification only, not a response, does your post have the following four questions:

• What is this quality of being able to squish a bucket of custard flat slowly, but if you hit it with a hammer fast it stays the same shape and does not deform. What is this quality called, what causes it and how many polymers with these type of physical qualities are known and what are their names?
  
  How can something liquid or plastic have a quality of a solid when energy is applied?
  
  Do the laws of thermodynamics apply if you add energy to a system and entropy decreases?
  
  Is there a course on the net I can read up on thermodynamics

tristan512 wrote:Hi, on Mythbusters on TV they showed how if you put your hand slowly into a bucket of custard it will easily go up to your elbow but if you slap it with your hand the surface tension increases and it wont go in. you can even run across a pool of custard slapping your feet and not sink but if you stop still you will sink. Also on TV i saw a new material like placticine. you can squash it flat slowly but if you hit it with a hamer fast it stays the same shape and does not deform. what is this quality called, what causes it and how many polymers with these type of physical qualities are known and what are their names?
how can something lioquid or plastic have a quality of a solid when energy is applied. are the laws of thermodynamics in play here where if you add energy to a system the amount of entrophy decreases or is it something else.is there any resourse on the net i can read up on this that can help ?

My search turned up nothing, but a buddy of mine has lent a hand. According to him, you may be referring to something called a non-newtonian fluid. I found this link after searching again:

http://en.wikipedia.org/wiki/Non-Newtonian_fluid

The page there talks about custard as a generalized non-newtonian fluid.

Within that page, you'll see a link to this one:
http://en.wikipedia.org/wiki/Dilatant
which describes the specific fluid property that interests you.

http://www.military.com/NewsContent/0,1 ... 04.00.html

Here's the link to the military armor fluid currently under research. The mixture is of polyethylene glycol and amorphous nano-sized silica. The mixture is absorbed into clothing and kevlar as the armor.