Question

Even when no heat is exchanged by the contents of a thermos flask,the contents of a thermos flask get heated up by constant shaking. Why?

Answer 1

Because of the collisions of its molecules.....and also whatever the heat is generated by it ....it is not lost to the surrounding so it gets heated up.....

Answer 2

as we know that friction produces heat.

when we shake the thermos flask the molecules of content mainly liquid collide each other .as a result kinetic energy produced and hence friction comes into play. hence content gets heated