与速度成正比的力称为正比例线性力,形如f=kv.根据力与速度方向的关系,线性力可分为两种,一种是力与速度共线,另一种是力与速度垂直(如洛伦兹力始终与速度方向垂直).当力与速度共线时,力在一段时间Δt内的平均值为f=kv,则其冲量为 The force proportional to the velocity is called the proportional linear force, which is like f = kv. According to the relationship between force and velocity, the linear force can be divided into two kinds: one is force and velocity collinear and the other is force and velocity (Lorentz force is always perpendicular to the velocity direction.) When the force is collinear with the velocity, the force averaged over a period of time Δt is f = kv, then the impulse is