What is a variable force? Write the equation for the work done by a variable force in one dimension.

(N/A) variable force is a force whose magnitude or direction (or both) changes with time or position as an object moves. Examples include the spring force $(F = -kx)$ or gravitational force between two bodies at varying distances.
In one dimension,if a force $F(x)$ acts on an object,the work done $W$ as the object moves from an initial position $x_i$ to a final position $x_f$ is given by the integral of the force with respect to displacement:
$W = \int_{x_i}^{x_f} F(x) \, dx$