Đang chuẩn bị liên kết để tải về tài liệu:
Ebook Vector mechanics for engineers (9th edition): Part 2

Không đóng trình duyệt đến khi xuất hiện nút TẢI XUỐNG Tải xuống

(BQ) Part 2 book "Vector mechanics for engineers" has contents: Method of virtual work, systems of particles, mechanical vibrations, kinetics of rigid bodies in three dimensions, plane motion of rigid bodies - energy and momentum methods, plane motion of rigid bodies - forces and accelerations,.and other contents. | bee29400_ch10_556-599.indd Page 557 11/28/08 3:15:32 PM user-s172 /Volumes/204/MHDQ076/work%0/indd%0 C H A P T E R Method of Virtual Work 557 bee29400_ch10_556-599.indd Page 558 11/28/08 3:16:00 PM user-s172 *10.1 Chapter 10 Method of Virtual Work 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 Introduction Work of a Force Principle of Virtual Work Applications of the Principle of Virtual Work Real Machines. Mechanical Efficiency Work of a Force during a Finite Displacement Potential Energy Potential Energy and Equilibrium Stability of Equilibrium dr a A r O Fig. 10.1 A' INTRODUCTION In the preceding chapters, problems involving the equilibrium of rigid bodies were solved by expressing that the external forces acting on the bodies were balanced. The equations of equilibrium oFx 5 0, oFy 5 0, oMA 5 0 were written and solved for the desired unknowns. A different method, which will prove more effective for solving certain types of equilibrium problems, will now be considered. This method is based on the principle of virtual work and was first formally used by the Swiss mathematician Jean Bernoulli in the eighteenth century. As you will see in Sec. 10.3, the principle of virtual work states that if a particle or rigid body, or, more generally, a system of connected rigid bodies, which is in equilibrium under various external forces, is given an arbitrary displacement from that position of equilibrium, the total work done by the external forces during the displacement is zero. This principle is particularly effective when applied to the solution of problems involving the equilibrium of machines or mechanisms consisting of several connected members. In the second part of the chapter, the method of virtual work will be applied in an alternative form based on the concept of potential energy. It will be shown in Sec. 10.8 that if a particle, rigid body, or system of rigid bodies is in equilibrium, then the derivative of its potential energy with respect to a variable defining