Noise is generated from the movement of an object or the vibration of a noise source, thus generating noise waves, which compress and expand again and again until they hit a human’s nervous system or ears. Each source generates its own intensity depending on the intensity of the movement or the vibration of the noise source (Figure 2.22). The distance from a source also affects noise intensity since noise needs a medium to travel upon-in this case, the air. Therefore, weather (e.g., atmospheric temperature and humidity) must be taken under consideration when determining or predicting noise intensity.