When an object falls freely on the earth, the gravitational force acting on the body

The direction of acceleration will be the same as the force acting on the body. As we know, gravitational force will always attract and the direction of force will always be towards the centre of another body. and 'g' is acceleration due to gravitational force, so direction of force/acceleration would be towards the centre of earth. Also force will depend on distance between the two bodies so it is not constant.