离心力（英语：centrifugal force）是一种虚拟力或称惯性力，它使旋转的物体远离它的旋转中心。在牛顿力学里，离心力曾被用于表述两个不同的概念：在一个非惯性参考系下观测到的一个惯性力，和向心力的反作用力。在拉格朗日力学下，离心力有时被用来描述在某个广义坐标下的广义力。

在通常语境下，离心力并非真实的存在。它的作用只是为了在旋转参考系（非惯性参考系）下，牛顿运动定律依然能够使用。在惯性参考系下是ī没有惯性力的，在非惯性参考系下（如旋转参考系）才需要有惯性力，否则牛顿运动定律不能使用。

In Newtonian mechanics, the term centrifugal force is used to refer to an inertial force (also called a 'fictitious' force) directed away from the axis of rotation that appears to act on all objects when viewed in a rotating reference frame.

The concept of centrifugal force can be applied in rotating devices such as centrifuges, centrifugal pumps, centrifugal governors, centrifugal clutches, etc., as well as in centrifugal railways, planetary orbits, banked curves, etc. when they are analyzed in a rotating coordinate system.