Re: [Phys-L] ?conservation of _internal_ energy

[Herbert Schulz <herbs@wideopenwest.com>]

> On Jan 14, 2016, at 9:23 AM, Herbert Schulz <herbs@wideopenwest.com> wrote:
>
> > On Jan 14, 2016, at 8:57 AM, John Denker <jsd@av8n.com> wrote:
> >
> >
> > Therefore it may be helpful to look at a non-gravitational
> > example.  Consider the situation shown here:
> > https://www.av8n.com/physics/img48/internal-energy-noncon.png
>
> Howdy,
>
> Yes, imagine a gas instead of the spring. As the gas expands it pushes the piston and does work. The Temperature of the gas will go down and the Internal energy of the gas will go down. So yes, the Internal energy is not constant. What is your argument that the Internal energy SHOULD be constant?
>
> Good Luck,
>
> Herb Schulz
> (herbs at wideopenwest dot com)

Howdy,

Since you want to concentrate on the `blue' body let's make it really simple. Just have the `blue' body against an infinitely massive solid wall. When Spring/Gas expands the Internal energy (either the Potential energy stored in the spring or the Internal energy stored in the molecules of gas) of the `blue' body goes down (the Potential energy of the spring or Internal energy of the molecules of gas [i.e., the Temperature of the gas] goes down) while the Kinetic energy of the CM of the `blue' body goes up.

Good Luck,

Herb Schulz
(herbs at wideopenwest dot com)