Collisions in Two Dimensions二维碰撞
The result of a collision between two objects in a plane cannot be predicted from just the momentum and kinetic energy of the objects before the collision. However, the outcome is constrained to obey conservation of momentum, which is a vector relation. This means that if x and y coordinates are used in the plane, the x and y components of momentum as well as its total magnitude must be the same before and after the collision. The kinetic energy would be the same before and after the collision if the collision were perfectly elastic, but ordinary macroscopic collisions usually have significantly less kinetic energy after the collision because of transfer of energy into other forms. The only way you could have more kinetic energy after the collision would be in the case of some release of energy in the collision, e.g., in a chemical explosion. 在平面内两个物体碰撞的结果不能仅凭碰撞前物体的动量和动能来预测。然而，碰撞的结果必须遵守动量守恒，这是一种矢量关系。这意味着如果在平面中使用x和y坐标，碰撞前后动量的x和y分量以及其总大小必须相同。如果碰撞是完全弹性的，碰撞前后的动能将相同，但通常宏观碰撞后动能会显著减少，因为能量会转化为其他形式。唯一可能在碰撞后动能增加的情况是碰撞中释放能量，例如化学爆炸。
In the example calculation, the masses, velocities, and angles before the collision are specified. If one of the velocities (magnitude and direction) is specified after the collision, then conservation of momentum determines the other exactly. Examination of the kinetic energy after the collision helps to determine whether or not it is a reasonable outcome. Calculation计算 在示例计算中，碰撞前的质量和速度以及角度已被指定。如果碰撞后其中一个速度（大小和方向）被指定，那么动量守恒将确定另一个速度。检查碰撞后的动能有助于判断这一结果是否合理。 |
Index Collision concepts 索引 碰撞概念 | ||
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