Wegener also noted that the continents move up and down to maintain equilibrium in a process called isostasy. As an example he cited the sinking of Northern Hemisphere lands under the weight of continental ice sheets in the last ice age, and their rise since the ice melted some 10,000 years ago.
Drill bits are cutting tools used to create cylindrical holes, almost always of circular cross-section. Drill bits come in many sizes and have many uses. Bits are usually connected to a mechanism, often simply referred to as a drill, which rotates them and provides torque and axial force to create the hole.
What is the primary purpose of drill (drill and ceremony)? The purpose of drill is to enable a commander or non-commissioned officer to move his unit from one place to another in an orderly manner; to aid in disciplinary training by instilling habits of precision and response to the leader's orders;and to provide for the development of all soldiers in the practice of commanding troops.