The process that causes a material to change its state from gas to liquid is called condensation. Condensation occurs when a gas cools down and loses energy, causing its particles to slow down and come closer together. As the particles get closer, they start to attract each other more strongly and eventually form a liquid. The temperature at which a gas condenses is called its dew point. Condensation is the opposite process of evaporation, which is the process by which a liquid turns into a gas.