what is the temperature at which a solid changes into a liquid
Heat is probably the easiest energy you can use to change your physical state. The atoms in a liquid have more energy than the atoms in a solid. There is a special temperature for every substance called the melting point. When a solid reaches the temperature of its melting point, it can become a liquid. For water, the temperature needs to be a little over zero degrees Celsius (0 o C) for you to melt.