Dynamics Hibbeler Ch 14 Notes

8/12/2019 Dynamics Hibbeler Ch 14 Notes

http://slidepdf.com/reader/full/dynamics-hibbeler-ch-14-notes 1/6

Engineering Mechanics: Dynamics

CHAPTER 14 KINETICS OF A PARTICLE: WORK AND ENERGY

14.1 THE WORK OF A FORCE

Force F will do work on a particle only when the particle undergoes a displacement in the direction of

the force

1. Interpretation

a. Product of F and the component of displacement, ds cos , in the direction of force b. Product of ds and the component of force, F cos , in the direction of displacement

1. when force is perpendicular to displacement

2. force applied to a fixed point where displacement is zero1. Work of a Variable Force

Work determined by integration using F and ∫ ∫

2. Work of a Constant Force Moving Along a Straight Line ∫ ∫ ∫ ( ) Constant magnitude F Constant angle

Work is the area of a rectangle



3. Work of a Weight Work is independent of the path and is equal to the magnitude of the particle’s weight (W)

times the vertical displacement ( ) ∫ ∫ ( ) ( ) ∫ ( ) Displacement is upward: -U Displacement is downward: +U

4. Work of a Spring Force Work of a spring works in the opposite sense Work of a spring:

∫ ∫

Avoid mistake in sign1. Use direction spring force and direction of displacement

Both in same direction: positive work

Both in opposite direction: negative work

14.2 PRINCIPLE OF WORK AND ENERGY

∑ ∑ ∑∫ ∫ ∑∫( )

∑ ( ) ∑ : All forces acting on the particle as the particle moves from point 1 to point 2



Work can be positive or negative, but kinetic energy is always positive

∑ ( ) ∑ ∑



14.3 PRINCIPLE OF WORK AND ENERGY FOR A SYSTEM OF PARTICLES

Principle of work and energy for a body can be applied to a system of particles ∑ ∑ ∑

Work of Friction Caused by Sliding

14.4 POWER AND EFFICIENCY

⁄ ⁄ ⁄

Efficiency is always less than 1 Output is less always than input



14.5 CONSERVATIVE FORCES AND POTENTIAL ENERGY

14.6 CONSERVATION OF ENERGY



Documents

Dynamics Hibbeler Ch 14 Notes