Aluminum and acrylic rods are mounted on a Braun electroscope to illustrate the difference between conductors and insulators. When a charged rod is brought close to the aluminum rod, the electroscope shows a significant deflection due to the aluminum conducting the charge, allowing the electrons to move freely. In contrast, when the charged rod is brought near the acrylic rod, there is minimal deflection on the electroscope, indicating that the acrylic does not conduct the charge as it is an insulator. This demonstrates how conductors allow the free movement of charge, while insulators do not.