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In SI units, this acceleration is expressed in metres per second squared (in symbols, m/s 2 or m·s −2) or equivalently in newtons per kilogram (N/kg or N·kg −1). Near Earth's surface, the acceleration due to gravity, accurate to 2 significant figures, is 9.8 m/s 2 (32 ft/s 2).
It is a constant defined by standard as 9.806 65 m/s 2 (about 32.174 05 ft/s 2). This value was established by the third General Conference on Weights and Measures (1901, CR 70) and used to define the standard weight of an object as the product of its mass and this nominal acceleration .
Newton's second law states that force equals mass multiplied by acceleration. The unit of force is the newton (N), and mass has the SI unit kilogram (kg). One newton equals one kilogram metre per second squared. Therefore, the unit metre per second squared is equivalent to newton per kilogram, N·kg −1, or N/kg. [2]
It has dimension of acceleration (L/T 2) and it is measured in units of newtons per kilogram (N/kg) or, equivalently, in meters per second squared (m/s 2). In its original concept, gravity was a force between point masses.
Near the surface of the Earth, the acceleration due to gravity g = 9.807 m/s 2 (metres per second squared, which might be thought of as "metres per second, per second"; or 32.18 ft/s 2 as "feet per second per second") approximately. A coherent set of units for g, d, t and v is essential.
For example, a stiff and compact object dropped from 1 m that impacts over a distance of 1 mm is subjected to a 1000 ɡ 0 deceleration. [citation needed] Jerk is the rate of change of acceleration. In SI units, jerk is expressed as m/s 3; it can also be expressed in standard gravity per second (ɡ 0 /s; 1 ɡ 0 /s ≈ 9.81 m/s 3). [citation needed]
Near the surface of the Earth, an object in free fall in a vacuum will accelerate at approximately 9.8 m/s 2, independent of its mass. With air resistance acting on an object that has been dropped, the object will eventually reach a terminal velocity, which is around 53 m/s (190 km/h or 118 mph [ 4 ] ) for a human skydiver.
A newton is defined as 1 kg⋅m/s 2 (it is a named derived unit defined in terms of the SI base units). [1]: 137 One newton is, therefore, the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.