Conduction, convection and radiation are ways energy can move between different objects or materials. In conduction, if there is a temperature gradient, due to collisions and diffusion, heat will move from the hotter to the cooler object. An example is when a pot is on the stove. The metal is heated by conduction and this in turn, heats the water molecules in the pot. Convection occurs in liquids and gases. Hotter air for example rises as the atoms move apart and get more excited. Then, as these molecules cool off, they become more dense and sink again. Convection currents are important ways heat energy is transferred in the ocean conveyor belt and in the atmosphere. Radiation is when energetic waves or particles travel through a vaccumm and do not need a medium to act as a conductor. An example is infrared radiation, Xrays and other electromagnetic waves. When sunlight, a form of radiation, passes through the vaccum of space and enters Earth's atmosphere, it is traveling as radiation.