velocity impact hardening

例句：

1. 1.The car accelerates to 60 miles per hour.
   汽车以每小时60英里的速度加速。
2. 2. The project will reach its goal in three months.
   这个项目将在三个月内达到其目标。
3. 3.The train is traveling at a constant velocity.
   火车以恒定速度行驶。