And, it also describes the relationship between a particle's velocity and its mass.
并且，它还描述了粒子速度与其质量之间的关系。
Crash Course Physics 速成课物理
Then point your arm in the direction of the particle's velocity.
然后将你的手臂指向 粒子速度的方向。
英语百科
Particle velocity
Particle velocity is the velocity of a particle (real or imagined) in a medium as it transmits a wave. The SI unit of particle velocity is the metre per second (m/s). In many cases this is a longitudinal wave of pressure as with sound, but it can also be a transverse wave as with the vibration of a taut string.