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

没有静摩擦系小于动摩擦系况没有静摩擦系小于动摩擦系况。

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

动摩擦和静摩擦？有什么区别？

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

可以抵抗动摩擦 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，静摩擦系几乎总是大于动摩擦系。

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 斜坡并声称没有动摩擦。

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.

当两个表面相对滑动时，摩擦是动， 其公式为动摩擦力等于动摩擦系乘以法向力。