Heat transfer. A copper bar is heated over a Bunsen burner next to a beaker of water. After heating up to a sufficient temperature, this bar will contain enough energy to heat the beaker of water almost to boiling point. This is because metals and water are good conductors of heat, but air is not. While the copper is heated in air it retains the heat, but when put in water the heat quickly flows out of the metal and into the surrounding water. See photograph 2K8424 for the same experiment after immersion of copper in the water.