What machine converts mechanical energy into electrical energy?

A generator is the correct answer because it operates on the principle of electromagnetic induction, where mechanical energy is converted into electrical energy. When a generator's rotor spins, it creates a magnetic field that induces an electric current in the coils of wire, effectively transforming the kinetic energy from mechanical motion into usable electrical energy. This process is fundamental in various applications, from power generation in large power plants to smaller applications such as backup power systems.

The other options serve different functions: a motor transforms electrical energy into mechanical energy, enabling machines to perform work by converting electrical input into motion. A commutator is an essential component of some types of motors and generators, facilitating the conversion of current direction but does not perform energy conversion itself. A power supply provides electrical energy for devices but does not convert mechanical energy into electrical energy; it supplies the necessary power for operation.