see while freefall only g isacting

 

now a = v dv/dx (derive it its easy)

 

since v is increasing per unti time with distance but remember that velocity increases increases linearly ie @ g per second but distance increases quadratically ie 1/2 g t² . so obviously distance increases faster than velocity....as per equation given above dv/dx *  v is a constant ie g in this case.And u can intuitively understand that when velocity has increased by g the distance has increased by much more than due to the square so dv/dx changes....emply these in equation of motion to get a cleearer picture!!!