A fluid is a substance that continually deforms (flows) under an applied stress. In science, a fluid can be either a liquid or a gas; however, in common usage, the term "fluid" is most often used synonymously with "liquid." Liquids are differentiated from gasses in that they have a boundary between the substance and the surrounding air caused by surface tension, a property unique to liquids. The term fluid can also be used to describe movement "in a smooth and graceful way that seems relaxed."
Your challenge is to convey the concept of fluid in your images. I've included a few example images that I thought successfully conveyed fluid. Do you see anything in common between the images? Almost all of them effectively use soft light to provide modeling and convey the three-dimensional, rounded forms of a flowing liquid. Most of the images also use motion, or soft blur caused by motion, to convey the movement or flow of the liquid. Several of the images also convey a sense of "smooth and graceful rhythm" to the movement of the liquid.
(http://spiritofphotography.com/coppermine/albums/userpics/10001/20091009_094728_v3.jpg)
Autumn Stream
Photographed by Keith
(http://spiritofphotography.com/coppermine/albums/userpics/10126/3865-2.jpg)
Fog Over the Falls
Photographed by Todd Obiedo
(http://spiritofphotography.com/coppermine/albums/userpics/10126/6813-2.jpg)
Sunset Reflection
Photographed by Todd Obiedo
(http://spiritofphotography.com/coppermine/albums/userpics/10001/DSC_2986_Cereal___Milk_sharpened.jpg)
Cereal and Milk
Photographed by Rick Pepin (trvlrick)
Your assignment for the week of 6 - 12 September 2010 is "Fluid." Please upload your images to the "Fluid" album in the Weekly Assignment category of the Gallery no-later-than midnight Mountain Time (GMT -07:00) on Sunday, 12 September 2010.
I'll look forward to seeing your images.
Keith