(3) An implication(暗示) what is known as inertial reference frame- those special reference frame in which Newton's law is valid Figure 2-1 A test to tell a reference frame is inertial or not Question: Try to give some examples to say why or why not a reference frame is an inertial reference frame
⑶ An implication（暗示） what is known as inertial reference frame — those special reference frame in which Newton’s law is valid. Question: Try to give some examples to say why or why not a reference frame is an inertial reference frame
Figure 2-1 A test to tell a reference frame is inertial or not Move on the surface of mars Fly from Earth to Mars Conclusion(结论):??
Move on the surface of Mars Fly from Earth to Mars Conclusion（结论）:??
2. Newton's second law Newton's second law of motion can be summarized in a simple vector equation F na (2-1) 外力 It is expressed in word as: A external force acting on a body produces an acceleration which is in the direction of the force and has a magnitude inversely proportional to反比于 the mass of the bod
2. Newton’s Second Law Newton’s second law of motion can be summarized in a simple vector equation： It is expressed in word as: A external force acting on a body produces an acceleration which is in the direction of the force and has a magnitude inversely proportional to反比于the mass of the body. F ma 外力 = (2-1)
To understand Newton's second law, we must note what physical meanings it includes (1Newton's second law is valid (有效) only in particles or the obiects that can be regarded as particle particle 可看成
To understand Newton’s Second Law, we must note what physical meanings it includes. (1)Newton’s second law is valid （有效） only in particles or the objects that can be regarded as particle. particle 可看成
(2)If several external forces F,E, F b.,... act simultaneously(同时) on a body,is acceleration is the sum of these produced by a single force given by
(2) If several external forces ... ... act simultaneously （ 同 时 ） on a body, its acceleration is the sum of these produced by a single force given by F F ,F , F F F a