In physics and acoustics, sound intensity is directly related to the power and area of a sound wave, and can be represented by the equation I=PA, where P is power and A is area. The SI unit for sound intensity is W/m2. As the distance increases, the intensity decreases according to the inverse square law, meaning that each time the distance is doubled, the intensity is cut by a factor of four. This decrease in intensity also corresponds to a decrease in sound level, with a decrease of 3 dB for every halving of intensity. This relationship can be seen in a variety of scenarios, such as a drum head or a point source of acoustic sound. When calculating sound attenuation over distance, the intensity in decibels can be compared to the threshold of hearing, and the inverse square law is applied to determine the decrease in intensity over distance.