1. Work and Energy Two interrelated quantities

2. Word Bank for Work & Energy Unit Force Energy Momentum Conserved quantities Work Joule Total energy Kinetic energy Translational kinetic energy Potential energy Gravitational potential energy Reference level for PE g Conservative/Dissipative forces Law of Conservation of Energy Power

3. Definition of Work Work done on a particle by a constant force (constant both in magnitude and direction) is defined as the dot (scalar) product of force and displacement i.e., the product of magnitude of the displacement and the component of force parallel to the displacement. W = F·d = (Fcosθ)d = Fdcosθ SI unit of work is the Joule where 1 J = 1N·m Other units centimetre-gram-second system (cgs) 1erg = 1 dyne·cm (10 5 dyne = 1 N) Imperial system (IS? Not SI ) foot-pound

4. If the displacement is along the +x axis, neither the normal force nor the gravitational force will do work. They are both perpendicular to the displacement ie θ = 90º so cosθ = 0 Refer to example 6-1, 6-2 in Giancoli p.126

5. Work done by a varying force For the work done by a variable force, graphical techniques may be used. An exact answer may be found from integral calculus. Fcosθ vs distance

6. Energy –one of the most imp concepts in science. It can be defined as the ability to do work (useful definition but not so precise). Moving objects can do work on other objects e.g. tackler and quarterback, hammer and nail, baseball and glove. Energy of motion is called “kinetic” energy.

7. The Work-Energy Theorem W = Fd = (ma)d = m [(v 2 – v o 2 )/2d]d W = ½ mv 2 – ½ mv o 2 Translational KE = ½ mv 2 So W = ΔKE The net work done on an object is equal to its change in kinetic energy. NB this is not a wireless network