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1、+ Text Only Site+ Non-Flash Version+ Contact GlennThis page is intended for college, high school, or middle school students. For younger students, a simpler explanation of the information on this page is available on theKids Page.Sir Isaac Newton first presented his threelaws of motionin the Princip
2、ia Mathematica Philosophiae Naturalis in 1686. His first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This is normally taken as the definition ofinertia. The key point here is that if
3、 there isno net forceresulting from unbalanced forces acting on an object (if all the external forces cancel each other out), then the object will maintain aconstant velocity. If that velocity is zero, then the object remains at rest. And if an additional external force is applied, the velocity will
4、 change because of the force. The amount of the change in velocity is determined by Newtonssecond lawof motion.There are many excellent examples of Newtons first law involving aerodynamics. The motion of anairplanewhen the pilot changes the throttle setting of the engine is described by the first la
5、w. The motion of aballfalling down through the atmosphere, or amodel rocketbeing launched up into the atmosphere are both examples of Newtons first law. The motion of akitewhen the wind changes can also be described by the first law. We have created separate pages which describe each of these examples in more detail to help you understand this important physical principle.