This law holds for both linear motion and forces and for twisting motion and twisting forces. Twisting forces are called torques , or moments. The twisting motion must occur about some point called the pivot . An excellent way for students to gain a feel for the effects of forces is to fly a kite .
Kites can fly because of the forces acting on the parts of the kite.
Though kites come in many shapes and sizes, the forces which act on any kite are the same as the forces acting on an airliner in flight with the exception of thrust. The similarity in forces allowed the Wright brothers to test some of their theories of flight by using a kite in 1900. There are, however, some important differences in the response of a kite to external forces that do not occur in an airplane. An airplane in flight will rotate about its center of gravity . The center of gravity is the average location of the weight of all the parts of any object.