What is physical weathering and chemical weathering?

Physical weathering:

Physical weathering is the disintegration of rock by mechanical processes and therefore depends on the application of force. The applied forces could be: 

• Gravitational forces such as overburden pressure, load and shearing stress; 
• Expansion forces due to temperature changes, crystal growth or animal activity; 
• Water pressures controlled by wetting and drying cycles.

Chemical weathering:

Chemical weathering is the weakening and subsequent breakdown of rocks by chemical reactions. A group of weathering processes viz; solution, carbonation, hydration, oxidation and reduction act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids. 

Further Reading:

• Chemical Weathering 
• Physical Weathering