# Work transfer to the contents of an ideal thermos flask

Assuming the thermos to be ideal and the fluid stored inside it also ideal and non-viscous. For a cold fluid, is it possible to increase the fluid's temperature by shaking the thermos flask? Can the kinetic energy provided by the motion be used to increase the energy of the fluid and thereby its temperature? How efficient will the process be?

• Sorry only saw ideally insulated thermos. See my edited answer – Bob D May 3 at 17:04
• By the way I believe no such fluid exists – Bob D May 3 at 17:08
• Check out Joule, Rumford and cannon barrels with a publication in 1798 about heat. – Solar Mike May 3 at 17:56

Assuming the thermos to be ideal and the fluid stored inside it also ideal. For a cold fluid, is it possible to increase the fluid's temperature by shaking the thermos flask?

Yes, but only if it were a real and not ideal fluid. The rest of my answer assumes a real fluid.

Can the kinetic energy provided by the motion be used to increase the energy of the fluid and thereby its temperature?

Shaking the contents can raise the temperature of the fluid. This causes viscous friction within the fluid due to your shaking. It's the viscous friction within the fluid that causes the temperature rise. When you shake the contents it is similar to what is called "stirrer work"- i.e. as if there were a paddle wheel inside the chamber that is rotated by a shaft extending outward. This was the basis of the famous Joule stirrer experiment where he demonstrated the equivalence of mechanical work and heat. You can look it up on the internet.

How efficient will the process be?

Not very. I believe the temperature rise was very little in the Joule experiment

Heating 1 kg of water 1°C requires 4182 J. Dropping 1 kg of water from a height of 1 m imparts 9.81 J of kinetic energy to the water, which ultimately turns into heat energy when the water slams into the ground. This raises the temperature by $$9.81/4182 = 0.0023$$ °C, so the effect is quite small.