So how the ultrasonic sensor works????
Well this more easy than it sounds like. This tutorial helped me a lot to understand the mechanism so I totally recommend it to you!! http://www.youtube.com/watch?v=PG2VhpkPqoA
So basically what this Sensor does is to send an ultrasonic wave from the Trigger pin. This wave travels until it hits an obstacle. Then the Echo pin receives the returning wave and Sends this detail to the arduino. Then the arduino with a simple mathematical calculation it calculates the distance.So simple!!!