Glass is an insulator which can be charged by rubbing because charges remain static on its surface. Iron is conductor which cannot be charged by rubbing because charges instantly flow towards the earth by human body or flow towards the iron from earth to make it neutral. Therefore, iron cannot be charged by rubbing.

Charging by Rubbing
When charging objects through rubbing, the process involves transferring electrons from one material to another. This phenomenon is dependent on the materials' ability to gain or lose electrons.
Material Properties
- Insulators vs. Conductors:
- Glass is an insulator and does not allow free flow of electrons.
- Iron, being a conductor, allows electrons to move freely.
- Electron Affinity:
- Different materials have varying tendencies to gain or lose electrons.
- Glass has a higher affinity for electrons compared to iron.
Rubbing Mechanism
- Friction:
- Rubbing induces friction, which helps in the transfer of electrons.
- This friction can create a charge separation in insulators like glass.
- Electron Movement:
- In glass, when rubbed, electrons are displaced from one area to another, creating a net charge.
- In iron, the free electrons can easily redistribute throughout the material, preventing localized charge buildup.
Conclusion
- Charge Retention:
- Glass can retain the charge since it does not allow electrons to flow freely.
- Iron, however, quickly equalizes any charge due to its conductive nature.
- Practical Implications:
- This is why glass rods can hold a charge when rubbed, while iron rods cannot achieve the same effect.
Understanding these differences is essential for applications in electrostatics and materials science.