The gravity of Earth, which is denoted by , refers to the acceleration that the Earth imparts to objects on or near its surface due to gravity. In SI units this acceleration is measured in metres per second squared (in symbols, m/s² or m·s^-2) or equivalently in newtons per kilogram (N/kg or N·kg^-1). It has an approximate value of 9.8 m/s², which means that, ignoring the effects of air resistance, the speed of an object falling freely near the Earth's surface will increase by about per second every second, this quantity is sometimes referred to informally as little (in contrast, the gravitational constant  is referred to as big ).