Newton's second law F-
Newton’s second law F ma =
Dynamics is to study the forces and their effects on the motions of obiects Ford 1913 In this chapter, we shall see that the cause of acceleration is a force exerted (使于) by some external(外部的) agent(力量) or environment(环境)
Dynamics is to study the forces and their effects on the motions of objects. In this chapter, we shall see that the cause of acceleration is a force exerted （使于） by some external（外部的） agent(力量） or environment（环境）
s2-1 Newton's Laws Force Inertial(惯性) Reference frame 1 Newton’ first law( The law of inertia惯性) A body at rest remains (te 持) rest and a body in motion continues to move at constant(但定) velocity unless acted upon by an external force(外力)
§2-1 Newton’s Laws Force Inertial（惯性）Reference Frame 1.Newton’ First Law （The Law of Inertia惯性） A body at rest remains（保 持 ） rest and a body in motion continues to move at constant（恒定） velocity unless acted upon by an external force（外力）
It should be noted: (1)An important property of all bodies- Inertia, the tendency(趋势) of bodies to maintain their original(原来的) state of motion. The force,not being the cause of motion of body, is the cause of change of motion of a body. D
⑴ An important property of all bodies — Inertia, the tendency（趋势） of bodies to maintain their original（原来的） state of motion. The force, not being the cause of motion of body, , is the cause of change of motion of a body. It should be noted:
(2)A qualitative definition of the concept of force as that which changes the state of motion Eon F2l The changes of their motions are same Conclusion (结论):F2>F1
⑵ A qualitative definition of the concept of force — as “that which changes the state of motion. F F The changes of their motions are same Conclusion（结论）: F F