Food coloring in glycerine is mixed by turning a drum, then unmixed by reversing. Has entropy decreased?
What it shows:
Ink is squirted into a fluid and mixed in until it disappears. By precisely undoing the motions in the reverse direction, the ink becomes unmixed! The demonstration seems to defy thermodynamics in that it appears that entropy decreases, but in actuality the reversible mixing is made possible by insuring that the mixing/unmixing is done without turbulence.
How it works:
The space between two, transparent and concentric...
Sodium 'D' line absorption showing up as a black line in the yellow of a continuous spectrum. Good as a simulation of the sodium portion of the Fraunhoffer absorption spectrum caused by atoms in the solar atmosphere; it does not however, resolve the 5890/5896Å doublet.
How it works:
As in the Sun, which is a black body source surrounded by an atmosphere of cooler gas containing many heavy atoms including sodium, we can set up a black body spectrum using a slide projector, and provide a hot sodium 'atmosphere' using...
As shown in the drawing, the Mercator projection is a cylindrical map projection of the spherical globe. The meridians and parallels of latitude on the globe end up appearing as lines crossing at right angles in the projection. Areas on the globe far from the equator appear to be much larger on the projection. It's not trivial to visualize this projection and the intention of this demonstration is to shed some light on it (literally).
Hydrogen peroxide 30% in a large round flask decomposes to boiling water and oxygen when postassium iodide is added.
The 12L Round Bottom Flask is set on white C-Fold towels covering a large cork ring on the lab bench. 100-150 ml of 30% hydrogen peroxide is carefully poured in. The liquid should be visible against the white towels from the perspective of the class, and any camera, if used.
The catalyst is 5 g of potassium iodide in a small plastic weighing boat labeled KI.
Safety goggles and gloves. Raise the projection screen and make sure the flask is...
An egg size piece of clear ice is dropped into a hot frying pan, with hissing and melting and steaming from solid to liquid to gas . An egg is carefully dropped into another hot frying pan, and it transforms from liquid to solid.
A small water bottle in the freezer overnight will freeze solid. Cutting off the plastic and breaking the ice with a hammer will generate the egg size piece of ice.
For a body to reach terminal velocity when falling through a fluid, the drag force (given by Stoke's Law) coupled with the buoyant force (from Archimedes' principle) need to balance the falling object's weight. Leaving derivations to other great texts you end up with