Heat

• The most obvious reason for ice melting is the presence of heat. If you point a hair dryer at some ice, or leave ice out in a room-temperature area for while, it will melt. This is because the temperature of the ice is rising, thus turning it into liquid water. The more heat you put on the ice, the quicker it melts, as higher heat will raise the ice's temperature quicker. This is why ice in a pan on the stove melts faster than ice left on top of the refrigerator.
  
  

Movement

• Movement also melts ice, for the same reason that heat does. When you move something, heat is created as a product of the energy transfer. Try rubbing your desk vigorously--your hand will start to feel warm. So, if you put ice in a container and shake it, it will start to melt, even though you have not applied any external heat.
  
  

Pressure

• Ice melts when you apply pressure to it, too. Pressure, like rapid movement, is a transfer of energy from one place to another. Energy transfers are never 100 percent efficient, and waste is always created. In the case of pressure, this waste is in the form of heat. So, you can melt ice by stacking things on top of it. The heat generated by the pressure melts the ice and turns it into water.
  
  

Salt

• Ice melts because the water molecules move faster when heat is applied to them. Conversely, water freezes because the water molecules slow down. If ice and water are mixed together, the ice will slow down some of the water molecules while the water will speed up some of the ice molecules. To freeze water, ice needs to bind with a moving water molecule and slow it down.
  
  Salt stops this process by making the binding process more difficult. A salt molecule is like a square peg while the ice molecules are round holes. The process of binding to liquid water molecules is made more difficult, and the ice starts to melt, regardless of temperature.
  
  Of course, the lower the temperature, the stronger the ice molecules will be and the more salt necessary to melt the ice.