Ch. 11 Energy I: Work and kinetic energy ch 11 Energy I: Work and kinetic energy
Ch.11 Energy I: Work and kinetic energy Ch. 11 Energy I: Work and kinetic energy
11-1 Work and energy Example: If a person pulls an object uphill. After some time, he becomes tired and stops We can analyze the forces exerted in this problem based on Newtons Laws, but those laws can not explain: why the man's ability to exert a force to move forward becomes used up For this analysis, we must introduce the new concepts of Work and Energy ch 11 Energy I: Work and kinetic energy
Ch.11 Energy I: Work and kinetic energy 11-1 Work and energy Example: If a person pulls an object uphill. After some time, he becomes tired and stops. We can analyze the forces exerted in this problem based on Newton’s Laws, but those laws can not explain: why the man’s ability to exert a force to move forward becomes used up. For this analysis, we must introduce the new concepts of “Work and Energy
Notes: 1)The "physics concept of workis different from the work in daily life of its 2)The" of a system is a measure its capacity to do work ch 11 Energy I: Work and kinetic energy
Ch.11 Energy I: Work and kinetic energy Notes: 1) The “physics concept of work” is different from the “work in daily life”; 2) The “energy” of a system is a measure of its capacity to do work
11-2 Work done by a constant force 11-3 Power 1. Definition of work The work W done by a constant force f that moves a body through a displacement s in the directions of the force as the product of the magnitudes of the force and the displacement W=FS (Here S/F)(11-1) ch 11 Energy I: Work and kinetic energy
Ch.11 Energy I: Work and kinetic energy 11-2 Work done by a constant force 1.Definition of ‘Work’ The work W done by a constant force that moves a body through a displacement in the directions of the force as the product of the magnitudes of the force and the displacement: (11-1) F s W = Fs (Here ) s//F 11-3 Power
EXample: In Fig 11-5, a block is sliding down a plane The normal force n does zero work; the friction force f does negative work, the gravitational force mg does positive work which g s mgs o= mgh Fig 11-5 or mgs cos =s(mg cos o) ch 11 Energy I: Work and kinetic energy
Ch.11 Energy I: Work and kinetic energy The normal force does zero work; the friction force does negative work, the gravitational force does positive work which is or → N → N mgscos = mgh mgscos = s(mg cos) → m g → m g → f s h v Fig 11-5 → f Example: In Fig11-5, a block is sliding down a plane