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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.
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density.
The steradian (sr) is equal to one (1). The newton (N) is equal to one kilogram-metre per second squared (1 kg⋅m⋅s −2). The pascal (Pa) is equal to one newton per square metre (1 N⋅m −2). The joule (J) is equal to one newton-metre (1 N⋅m). The watt (W) is equal to one joule per second (1 J⋅s −1).
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] Thus, the Earth's gravitational field (near ground level) can be quoted as 9.8 metres per second squared, or the equivalent 9.8 N/kg.
[1] An SI derived unit is a named combination of base units such as hertz (cycles per second), newton (kg⋅m/s 2), and tesla (1 kg⋅s −2 ⋅A −1) and in the case of Celsius a shifted scale from Kelvin. Certain units have been officially accepted for use with the SI.
1 kg = (299 792 458) 2 / (6.626 070 15 × 10 −34)(9 192 631 770) h Δν Cs / c 2 . All units in the SI can be expressed in terms of the base units, and the base units serve as a preferred set for expressing or analysing the relationships between units.
The General Conference on Weights and Measures fixed the value of standard gravity at precisely 9.80665 m/s 2 so that disciplines such as metrology would have a standard value for converting units of defined mass into defined forces and pressures. Thus the kilogram-force is defined as precisely 9.80665 newtons.
Some units have special names, however these should be treated like their equivalents. For example, one newton (N) is equivalent to 1 kg⋅m/s 2. Thus a quantity may have several unit designations, for example: the unit for surface tension can be referred to as either N/m (newton per metre) or kg/s 2 (kilogram per second squared).