So, these waves carry away energy from the ship, the generation of waves will require energy and since they are completely travelling they are carrying energy with them, so this energy will have to be supplied by the ship, which we call the wave making resistance, the force that generates this energy, we call it the wave making resistance is that clear? We have said that this is due to pressure. So, if I actually calculated the pressure around the ship hull whole body and calculated the longitudinal components and integrated it over the whole length of the ship, I will get a certain resistance, I will call it pressure resistance. Now, I have generated these waves, the final wave form that is behind the ship, if I take the total energy content by making a wave cut on the free surface, measuring the wave profile and seeing the rate at which the wave is travelling, this elevation is changing, I will get the force required for generating this energy experimentally I can find it out, that is called the wave making resistance. Now, people have done a number of experiments leaving aside the errors coming due to the existence of bounded layer, it has been found that the wave making resistance and the pressure measurement on the body surface and integration of it gives nearly same result. So, we can say with certain amount of clarity that wave making resistance and the pressure resistance resistance due to generation of normal pressures on the body surface are same.