Specific force

Specific force is defined as the force per unit mass.

${\mbox{Specific Force}}={\frac {\mathrm {Force} }{\mathrm {Mass} }}$

Specific force is measured in meters/second² (m·s^-2). Specific forces are not accelerations. Forces and specific forces are the the same in all reference frames, accelerations are frame dependent. For free bodies, the specific force is the cause of an acceleration. For bodies constrained from accelerating, the specific force will not equal the acceleration.

Gravitational acceleration is a specific force. The acceleration of an object free falling towards the earth depends on the reference frame, but the gravitational "acceleration" in all frames.

Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating. Accelerometers measure specific force, not acceleration.

Hydraulics

In open channel hydraulics, specific force (symbol F_s) has a different meaning:

• F_s = y²/2 + (q²)/gy

where q is the discharge per unit width (q = Q/B) and y is the flow depth.

See also

• Acceleration
• Proper Acceleration