“守恒”是自然界的基本规律，也是中学物理的重点．中学物理中用的比较多的是质量守恒定律、电荷守恒定律、动量守恒定律、能量转化及守恒定律．这在９９年的高考题中得到了较全面的体现，占总分的１／３．可见“守恒”定律在物理学中占有举足轻重的位置． 一、质量守恒定律、 “Conservation” is the basic law of nature, but also the focus of high school physics. Middle school physics is more used in the law of conservation of mass, the law of conservation of charge, the law of conservation of momentum, energy conversion and conservation laws. This 99 years of the college entrance examination has been more fully reflected, accounting for 1/3 of the total score. Visible “conservation” law holds a pivotal position in physics. First, the law of conservation of mass,