Respuesta :

When a solid is heated, the particles are given more energy and start to vibrate faster. ... The temperature at which this change from solid to liquid happens is called the melting point. Each solid has a set melting point at normal air pressure. At lower air pressure, such as up a mountain, the melting point lowers.
mathssydney
When solid object changes into liquid, it's energy increases. Saying more scientifically, an energy is added into system from external source.