 Let me answer. I am your partner in this video. The answer is very simple. Transfer of heat from hot place to cold place. Heat flows from hot to cold objects. When hot and a cold body are in thermal contact they exchange heat energy until they reach thermal equilibrium as shown in the graph on my left with the hot body cooling down and the cold body warming up. This is a natural phenomenon we experience all the time. Metals are good conductors of heat. The outer electrons of metal atoms are not attached to any particular atom. They are free to move between the atoms. When a metal is heated, the free electrons gain kinetic energy. This means that the free electrons move faster and transfer the energy through the metal. This makes heat transfer in metals very efficient. When one end of a metal bar is heated, molecules at this end begin to vibrate faster and faster. These particles at the hot end have a greater kinetic energy of vibration in comparison to the particles that are not directly under heat exposure. The electrons in a piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now positively charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by free electron. This heat transfer take place by conduction. The atoms in the glass radar held together by chemical bonds. The atoms are fixed in place but are free to vibrate. When part of a solid absorbs heat energy, the atoms vibrate faster and with bigger amplitude, these vibrations pass from atom to atom transferring heat energy as they do so. This process happens in all solids when heated but is a slow process since in solids molecules are closely packed and the mean free path of molecules is very very less than the overall dimensions heat transfer occurs due to diffusion. Basically, conduction is a diffusion process. Conduction is more common to solids but in principle it can and does happen in liquids and gases just not very well because the molecules of fluids have a greater freedom of motion than in solids. There is less of a chance that vibrating molecules will collide with another and transfer energy throughout the fluid. In fact, air is such a poor conductor that it is used to help insulate homes. Some energy efficient windows have air spaces between them that create a pocket of air between the inside of the home and the cold outside air because air does not conduct heat very well. More heat stays inside the home since the air makes it difficult for this thermal energy to make its way outside. I hope you enjoyed the video please don't forget to subscribe physics partner channel and like the video thank you