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ISO 31-3 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to mechanics. It is superseded by ISO 80000-4.
Its definitions include (note boldfaced symbols mean quantity is a vector):
Quantity | Unit | Remarks | |||
---|---|---|---|---|---|
Name | Symbol | Name | Symbol | Definition | |
Force | F | newton | N | 1 N = 1 kg·m/s2 | Unit named after Isaac Newton |
Moment of force, Torque | M, | N·m | 1 N·m = 1 kg·m2/s2 | The unit is dimensionally equivalent to the units of energy, the joule; but the joule should not be used as an alternative for the newton metre. | |
Linear momentum | p | kg·m/s or N·s | |||
(Linear) impulse | J | N·s or kg·m/s | |||
Angular momentum | L | kg·m2/s or N·m·s | |||
Mechanical energy, Work | E, W | joule | J | 1 J = 1 kg·m2/s2 = 1 Pa·m3 = 1 W·s | Unit named after James Joule. The joule is dimensionally equivalent to the units of torque and moment of force but should be used in preference to the newton metre (N·m). |
Power | P | watt | W | 1 W = 1 J/s = 1 N·m/s = 1 kg·m2/s3 | Unit named after James Watt. |
Pressure | p | pascal | Pa | 1 Pa = 1 N / m2 = 1 kg/(m·s2) | Named after Blaise Pascal. |
Normal stress, Shear stress | pascal | Pa | 1 Pa = 1 N / m2 = 1 kg/(m·s2) | Named after Blaise Pascal. | |
... |
Force
editForce is needed to accelerate objects with mass and is defined in Newton's second law of motion which states that
Moment of force, Torque
editTorque is analogous to force in the context of rotation and is described by the formula using the cross product
Linear momentum
editNewton's second law of motion also relates to momentum with the following expressions:
Photons also have momentum proportional to their energy.
(Linear) impulse
editAn impulse is described as force over time which is force integrated over time.
Angular momentum
editAngular momentum is analogous to linear momentum where angular velocity is used instead of linear velocity.
where I represents inertia and replaces mass and is angular velocity instead of linear velocity.
Mechanical energy, Work
edit
Power
editPressure
editNormal stress, Shear stress
edit...
References
editExternal links
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