But for other materials, the kinetic friction can be lower than static friction.

没有静擦系小于擦系况没有静擦系小于擦系况。

Kinetic Friction and Static Friction? What's the difference?

擦和静擦？有什么区别？

Kinetic friction will also often generate heat or sound or both.

它还可以抵抗擦 热量，声音，或两者兼而有之。

Also, for two surfaces, the coefficient of static friction is almost  always more than the coefficient of kinetic friction.

此外，对于两个表面，静擦系几乎总是大于擦系。

Like the time we rolled a bunch of stuff down a ramp, and pretended that there was no kinetic friction.

就像我们推出一些东西时候 斜坡并声称没有擦。

When the two surfaces  are sliding relative to one another, the friction is kinetic and the equation  works out to be the force of kinetic friction equals the coefficient of kinetic  friction times the force normal.

当两个表面相对滑时，擦是， 其公式为擦力等于擦系乘以法向力。