Naked Science Forum

General Science => General Science => Topic started by: peppercorn on 06/08/2008 17:43:48

Title: If I hit some custard with a hammer, whre does the energy go?
Post by: peppercorn on 06/08/2008 17:43:48

Dilatant liquids, like custard, become highly viscous under shearing forces.

Does the custard act like a solid under these circumstances?

- Hence, would there be a audible 'crack' and heat released?

Title: If I hit some custard with a hammer, whre does the energy go?
Post by: graham.d on 07/08/2008 12:09:55

Custard can vary hugely. My guess is the energy goes in spreading the custard all around the room and over the holder of the hammer. A fair bit of energy would be dissipated when the hammer hits the custard container unless the custard is very deep, the hammer wielder was very weak, or the custard was extremely viscous indeed.

Title: If I hit some custard with a hammer, whre does the energy go?
Post by: RD on 07/08/2008 12:17:15

Brainiac Video: Walking on custard (http://www.youtube.com/watch?v=BN2D5y-AxIY).

Title: If I hit some custard with a hammer, whre does the energy go?
Post by: DonBrown on 16/08/2008 12:37:02

Since they didn't boil the mixture, that isn't like the custard you eat. It is just the mixture of cornflour and water. It is also made with a very much higher proportion of flour to liquid: to make custard, I think you'd add at least 10x more liquid.
What did puzzle me was the insistence on cornflour. If this is just starch, why would not wheat flour, rice flour, potato flour, etc. do just as well?  Is the starch the significant factor or is it the shape and size of the grains or something like that?
What other substances behave like this? What do they call this?
Why is this different from a very viscous liquid?

I have also seen cornflour/water mixtures subjected to strong vibrations, when they form interesting 3D patterns of standing waves.

Title: If I hit some custard with a hammer, whre does the energy go?
Post by: lyner on 17/08/2008 00:47:24

The difference is the way that its response changes depending on the 'time profile' of the impressed force. Corn starch is incredibly rigid to impulsive shocks but has low viscosity to slowly applied loads.
Best to try the experiment yourself. Put a tablespoonfull of cornstarch on a saucer with several drops of water and hit it / mix it with a spoon. You can play for hours.