Why is the sudden expansion or compression of a gas considered to be an adiabatic process ?

Can change in internal energy of an ideal gas be considered as an adiabatic process ?

Isothermal Expansion And Compression Process

In adiabatic process, the work involved during expansion or compression of an ideal gas is given by :

In adiabatic process, the work involved during expansion or compression of an ideal gas is given by :

In adiabatic process, the work involved during expansion or compression of an ideal gas is given by :

Assertion: In adiabatic expansion, temperature of gas always decreases. Reason: In adiabatic process exchange of heat is zero.

Assertion: In adiabatic expansion, temperature of gas always decreases. Reason: In adiabatic process exchange of heat is zero.

Is the free expansion of an ideal gas adiabatic ?