More generally, tension can be defined as a positive normal stress acting on a body. A stress is defined as a force acting on a surface. In the International System, it is measured in Pascals (Pa)(1Pa=1N/m²). The stress is a tensor, having nine components (3x3). The components in the diagonal of the tensor are the normal stresses. The word "tension" typically refers to any of these three quantities provided that they have a positive value. The word "compression" is use in the case of having negative normal stresses. It should be stressed that the words "Tension", "compression" and stress" refers to forces acting on surfaces. And example of this is the atmospheric pressure.