Heat transfer by conduction occurs when molecules vibrate and collide with each other. Here's a breakdown:

* Conduction: The transfer of heat through direct contact between substances.

* Molecular Vibration: All matter is made up of molecules, and these molecules are constantly vibrating.

* Collisions: When a warmer object comes into contact with a cooler object, the molecules of the warmer object vibrate more vigorously. These vibrations are transferred to the molecules of the cooler object through collisions.

In essence, the energy from the warmer object's vibrating molecules is passed on to the cooler object's molecules through a chain reaction of collisions. This is how heat is transferred by conduction.