Work—Force Acting Over a Distance

Chapter 10 covers the importance of fi>rce and fiirce-rdated parameters in engineering. What is meant by fiirce, pressure, modulus of elastidtj, impulsive fi>rce (fi>rce acdi over time), work (force acting over a distance) and moment (fi>tce acting at a distance) ate discussed in detail. 

Energy, energy is the capacitance to do work, and work is defined as the product of a force acting over a distance, that is. 

In this way, work is computed as a path integral of a force acting over a distance. In general, the path integral also treats cases where the force varies along the trajectory. 

Over the time increment dt, the force applied on the left-hand side of the element acts over a distance u dt, so the work done on the element from the left is Pu dt. The force on the right-hand boundary of the element k P + (dPIdh), dh, and it travels a distance (u + (dufdh), dh) dt, so the work done by the element on the surrounding fluid to the right is (P + (dP/dh), dh)(u + (dujdh), dh) dt. The net work done on the fluid element is the difference... 

Energy is measured in terms of its ability to perform work or to transfer heat. Mechanical work is done when a force / displaces an object by a distance d w =/ x d. The basic unit of energy is the joule. One joule is the amount of work done when a force of 1 newton acts over a distance of 1 m thus 1 J = 1 N-m. The newton is the amount of force required to accelerate a 1-kg mass by 1 m/sec2, so the basic dimensions of the joule are kg m2 s 2,Thc other two units in wide use, the calorie and the BTU (British thermal unit), are defined in terms of the heating effect on water. Because of the many forms that energy can take, there are a correspondingly large number of units in which it can be expressed. A few of these are summarized in Table 1. 

The study of energy and its transformation from one form to another is called fliermo namics. The formal definition of energy is the capacity to do work. An object possessing energy can perform work on another object. The formal definition of wmk is a force acting through a distance. If you push a chair across the room, you have done work you have exerted a force over a distance. 

The metric unit of energy is the product of the units of force and distance, or (kg m/sec ) x m, which is kg mVsec this unit is called the JOULE, J. The joule is thus the work done when a force of 1 newton acts over a distance of 1 meter. 

We know that mass and velocities, and therefore also acceleration, are affected by special relativity, and may suspect that this law also must be modified. Nevertheless, the work done on a system by a constant force acting over a small distance may still be expressed as... 

Work (w) Force acting on an object over a distance. 

The work of a force acting on a lattice of size b over a distance -bis approximately W - b ab, where a is the stress. According to the Griffith schane, the local concentration of stresses can be accounted for by a factor Llbf, where L is the linear parameter characteristic of the average linear dimension of defects. Overall, W b iUbf o = Vb, where V is the parameter with the dimensions of volume. In a real body, this parameter exceeds the elementary cell volume by one to two orders of magnitude. V can be viewed as the effective activation volume it is actually Zhurkov s structural factor, y. 

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