(Hopefully) simple thermodynamics question

[AxiomOfChoice]

Suppose you have a piston of ideal gas that's thermally isolated from its surroundings. You compress the gas by pushing down on the piston. Question: Does the temperature of the gas change, and why?

My answer: YES, it changes. Since $\Delta U = Q + W$, and work was done ON the gas (by compressing it), $\Delta U > 0$. Since the energy of an ideal gas is only dependent on the temperature of the gas, this implies $\Delta T > 0$.

 

[vlado_skopsko]

Yes, it is increasing because with the piston you increase the momentum of the molecules that are bouncing of it, increasing their speed and with that their kinetic energy, that is like hitting a tennis ball with a racket.
You see the equation in the right way.