When an external deforming force applied on the body produces change in length of body then it is longitudinal or tensile stress.
The formula for longitudinal or tensile stress is given as,
Tensile Stress = Force / Area
Longitudinal Stress is often seen in cylinder, pipe , wire etc. So we can also write it as,
Longitudinal Stress = Force/ Area
Longitudinal Stress = F / π r 2
we know that force can also be defined as Force = mass x acceleration due to gravity
Longitudinal Stress = m g/ π r 2
where m = unit length of mass, g= acceleration due to gravity and r= radius.