“work”的概念、定义、翻译、参考文献-科学参考

work

Physics

The work done by a force acting on a body is the product of the force and the distance moved by its point of application in the direction of the force. If a force F acts in such a way that the displacement s is in a direction that makes an angle θ‎ with the direction of the force, the work done is given by: W=F.scosθ‎. Work is the scalar product of the force and displacement vectors. It is measured in joules.

Mathematics

The work done by a force F during the time interval from t = t₁ to t = t₂ is equal to

$\int_{t_{1}}^{t_{2}} F . v d t = \int_{r_{1}}^{r_{2}} F \cdot d r,$

where v is the velocity of the point of application of F. The second integral is an alternative form, where r denotes displacement, so that dr/dt = v and r₁ and r₂ are the initial and final displacements.

From the equation of motion ma = F for a particle of mass m moving with acceleration a, it follows that ma. v = F. v, and this then gives

$(d / d t) (\frac{1}{2} m v . v) = F . v .$

By integration, it follows that the change in kinetic energy is equal to the work done by the force.

Suppose that a particle has displacement x(t)i is acted on by a constant force Fi in the same direction. Then the work done during the time interval from t = t₁ to t = t₂ equals

$\int_{t_{1}}^{t_{2}} F x' (t) d t = F (x (t_{2}) - x (t_{1})) .$

This is usually interpreted as ‘work=force × distance’.

The work done against a force F should be interpreted as the work done by an applied force equal and opposite to F. When the force is conservative, this is equal to the change in potential energy. When a person lifts an object of mass m from ground level to a height z above the ground, work is done against the uniform gravitational force and the work done equals the increase mgz in potential energy.

Work has the dimensions ML² T⁻², the same as energy, and the SI unit of work is the joule.

Chemical Engineering

The forms of energy transfer that can be accounted for in terms of changes in the external macroscopic-scale physical constraints on a system. The work done is the product of a force and the distance moved by its application. Displacement work is the energy that goes into expanding the volume of a system against an external pressure such as by driving a piston out of a cylinder against an external force or driving a piston into a cylinder of a given volume and pressure. Work done can also be achieved by a paddle acting upon a fluid or by a fluid, propeller, or turbine blade. Frictional work is the work done overcoming friction. The SI unit is the joule.

Economics

Activities involving physical and/or mental effort. While a large part of this is in paid employment, or working for economic gain while self-employed, there are other forms of work. This is recognized in the terms voluntary work, where people perform for charities or political parties tasks other people are paid for, and housework, where people work for the welfare of their families. See also hours of work; part-time work; shift work; skilled work; unskilled work.

单词	work
释义	work Physics The work done by a force acting on a body is the product of the force and the distance moved by its point of application in the direction of the force. If a force F acts in such a way that the displacement s is in a direction that makes an angle θ‎ with the direction of the force, the work done is given by: W=F.scosθ‎. Work is the scalar product of the force and displacement vectors. It is measured in joules. Mathematics The work done by a force F during the time interval from t = t₁ to t = t₂ is equal to $\int_{t_{1}}^{t_{2}} F . v d t = \int_{r_{1}}^{r_{2}} F \cdot d r,$ where v is the velocity of the point of application of F. The second integral is an alternative form, where r denotes displacement, so that dr/dt = v and r₁ and r₂ are the initial and final displacements. From the equation of motion ma = F for a particle of mass m moving with acceleration a, it follows that ma. v = F. v, and this then gives $(d / d t) (\frac{1}{2} m v . v) = F . v .$ By integration, it follows that the change in kinetic energy is equal to the work done by the force. Suppose that a particle has displacement x(t)i is acted on by a constant force Fi in the same direction. Then the work done during the time interval from t = t₁ to t = t₂ equals $\int_{t_{1}}^{t_{2}} F x' (t) d t = F (x (t_{2}) - x (t_{1})) .$ This is usually interpreted as ‘work=force × distance’. The work done against a force F should be interpreted as the work done by an applied force equal and opposite to F. When the force is conservative, this is equal to the change in potential energy. When a person lifts an object of mass m from ground level to a height z above the ground, work is done against the uniform gravitational force and the work done equals the increase mgz in potential energy. Work has the dimensions ML² T⁻², the same as energy, and the SI unit of work is the joule. Chemical Engineering The forms of energy transfer that can be accounted for in terms of changes in the external macroscopic-scale physical constraints on a system. The work done is the product of a force and the distance moved by its application. Displacement work is the energy that goes into expanding the volume of a system against an external pressure such as by driving a piston out of a cylinder against an external force or driving a piston into a cylinder of a given volume and pressure. Work done can also be achieved by a paddle acting upon a fluid or by a fluid, propeller, or turbine blade. Frictional work is the work done overcoming friction. The SI unit is the joule. Economics Activities involving physical and/or mental effort. While a large part of this is in paid employment, or working for economic gain while self-employed, there are other forms of work. This is recognized in the terms voluntary work, where people perform for charities or political parties tasks other people are paid for, and housework, where people work for the welfare of their families. See also hours of work; part-time work; shift work; skilled work; unskilled work.
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