Physics is also used back in the times of WW2 where submarine warfare became used. There would be these submarine hunter ships equipped with sonar technology that would patrol the water s searching for submarines. They would send out constant pulses into the water and if they sensed something out of the ordinary, they would drop depth charges. By detecting the enemy submarine, you can determine the depth in which the sub is at and then you can set the depth charges to the nearest 10 meters of the sub and hopefully blow the enemy out of the water. YAY PHYSICS!