Energy Work Kinetic Energy & Work-Energy Theorem Gravitational Potential Energy

Forms and Properties of Energy Forms Mechanical Chemical Electromagnetic Nuclear Properties Can be ______________ Total energy in universe remains ___________ Total energy in an ______ _______ remains constant First focus on mechanical energy

Definition of Work Not the same as our everyday definition The work, W, done by a constant force on an object is defined as the product of the component of force along the direction of displacement and the magnitude of the displacement. Work is a _______ quantity Unit is the Joule: 1 J = 1 N  m = 1 kg  m 2 /s 2

Work Fig. 5.1, p.120 Fig. 5.2, p.120 Fig. 5.3, p.120

Work Requires a System Work is done by something on something else Work has a sign (  or  ) Student does _______ work lifting box Student does _______ work lowering box Fig. 5.4, p. 121

Work and Kinetic Energy An alternative approach to solving problems Useful when forces are too ____________ to use F = ma If the net force on an object is in the ______ __________ as its displacement then cos  =1

Work and Kinetic Energy If F is constant then a is ________ If a is constant then ___________ give us: Kinetic Energy is ______ as Giving Kinetic Energy and Work have units of ______

Conservative Forces The work done by a conservative force in moving an object between 2 points is the same regardless of path 12 ΔxΔx Δs1Δs1 Δs2Δs2 Path a Path b Path c F

Nonconservative Forces The work done by a nonconservative force (e.g., friction) in moving an object between 2 points is not the same for different paths 12 ΔxΔx Δs1Δs1 Δs2Δs2 Path a Path b Path c

Work-Energy Theorem Update Rewrite to include work done by nonconservative forces as a __________ term

Potential Energy Is a property of a ______, not of ______ System: collection of objects interacting via forces _________ to the system Forces can do work on ________ to increase or decrease their potential energy Take a look at gravity and gravitational potential energy

Work & Gravitational Potential Energy Gravity can do work on objects This increases the object’s _______ _______ Fig. 5.12, p. 128

Work & Gravitational Potential Energy Recall connection between work and kinetic energy Relation between work and gravitational PE Work-Energy Theorem with gravity

Conservation of Energy For NO nonconservative forces W nc = __ Energy remains the same The total ___________ energy is constant

Nonconservative Forces When we have nonconservative forces (like friction), mechanical energy is not __________ (e.g., dissipated as heat)