What is Geostationary satellite ? State its uses.

The time period of an artificial satellite is equal to time period of rotation of earth then such
satellite is a geostationary satellite The time period of geostationary satellite is 24 hrs. Its
relative velocity with respect to earth is zero. 
Uses:
1) To study the size and shape of earth
2) To study the upper layers of atmosphere
3) To study the forecast changes in atmosphere
4)To detect the minerals and naturals
resources inside and on surface of earth
5) To undertake space research