Thermodynamics

Mixing and Unmixing

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...

Read more about Mixing and Unmixing
Adiabatic Heating

Compression of gas within bicycle pump heats gas; alternatively, syringe PV=nRT (w/ Mac TC read-out).

What it shows:

An adiabatic process is one where no heat enters or leaves a system. Here we compress a gas adiabatically inside a bicycle pump. The work done on the gas increases its internal energy, so increasing its temperature in accordance with the first law of thermodynamics.

Increase in internal energy dU = dW the work done on the system

How it works:

Instead of allowing the air out of a bicycle pump we've...

Read more about Adiabatic Heating
Bag of Lead Shot

Dropping bag containing lead turns gravitational potential energy to heat.

What it shows: 

A demonstration of the conversion of gravitational potential energy to heat energy. A bag of lead shot, repeatedly dropped to the ground, will heat up.

How it works: 

Lead has a sufficiently low specific heat capacity (128 J/kg/K) that a 5kg bag dropped five times from a height of 1.0m onto a rigid floor should increase in temperature by about 2K. The shot is contained in a bank deposit bag with reinforced...

Read more about Bag of Lead Shot
Vortex Tube

What it shows:

James Clerk Maxwell postulated that since heat involves the movement of molecules, it might be possible to separate hot and cold air in a device with the help of a "friendly demon" who would sort out and separate the fast and slow moving molecules of air. The vortex tube is such a device and does exactly that — using compressed air as a power source, it has no mechanical moving parts and produces hot air at one end and cold air at the other.

How it works:

Room temperature compressed air is supplied to the vortex tube...

Read more about Vortex Tube