The change of state from solid to liquid is called melting and from liquid to solid is called fusion.
It is observed that the temperature remains constant until the entire aount of the solid substance melts.
Both the solid and liquid states of the substance coexist in thermal equilibrium during the change of states from solid to liquid.
The temperature at which the solid and the liquid states of the substance is in thermal equilibrium with each other is called its melting point.
It is characteristic of the substance. It also depends on pressure.
The melting point of a substance at standard atmospheric pressure is called its normal melting point.
An activity to explain the process of melting of ice :
Take a slab of ice.
Take a metallic wire and fix two blocks, say 5 kg each, at its ends.
Put the wire over the slab as shown in Fig. You will observe that the wire passes through the ice slab.
This happens due to the fact that just below the wire, ice melts at lower temperature due to increase in pressure.
When the wire has passed, water above the wire freezes again. Thus the wire passes through the slab and the slab does not split. This phenomenon of refreezing is called regelation.
Skating is possible on snow due to the formation of water below the skates. Water is formed due to the increase of pressure and it acts as a lubricant.
