Sentence:  Two of the fluids showed a high positive normal <WSD>pressure</WSD> when undergoing shear , and two showed small negative pressures which were negligible in comparison with the amount of the positive pressures generated by the other two . 
Meaning of the word marked with <WSD> tags:  the force applied to a unit area of surface; measured in pascals (SI unit) or in dynes (cgs unit)