Definition of Work

1. Chapter 5 Section 1 Work Definition of Work • Work is done on an object when a force causes a displacement of the object. • Workis done only when components of a force are parallel to a displacement.

2. Chapter 5 Section 1 Work Definition of Work

3. Chapter 5 Section 1 Work Sign Conventions for Work Click below to watch the Visual Concept. Visual Concept

4. Chapter 5 Section 2 Energy Kinetic Energy • Kinetic Energy The energy of an object that is due to the object’s motion is called kinetic energy. • Kinetic energy depends on speed and mass.

5. Chapter 5 Section 2 Energy Kinetic Energy Click below to watch the Visual Concept. Visual Concept

6. Chapter 5 Section 2 Energy Kinetic Energy, continued • Work-Kinetic Energy Theorem • The net work done by all the forces acting on an object is equal to the change in the object’s kinetic energy. • The net work done on a body equals its change in kinetic energy. Wnet= ∆KE net work = change in kinetic energy

7. Chapter 5 Section 2 Energy Work-Kinetic Energy Theorem Click below to watch the Visual Concept. Visual Concept

8. Chapter 5 Section 2 Energy Potential Energy • Potential Energy is the energy associated with an object because of the position, shape, or condition of the object. • Gravitational potential energy is the potential energy stored in the gravitational fields of interacting bodies. • Gravitational potential energy depends on height from a zero level. PEg= mgh gravitational PE = mass  free-fall acceleration  height

9. Chapter 5 Section 2 Energy Potential Energy Click below to watch the Visual Concept. Visual Concept

10. Chapter 5 Section 2 Energy Potential Energy, continued • Elastic potential energy is the energy available for use when a deformed elastic object returns to its original configuration. • The symbol k is called the spring constant, a parameter that measures the spring’s resistance to being compressed or stretched.

11. Chapter 5 Section 2 Energy Elastic Potential Energy

12. Chapter 5 Section 2 Energy Spring Constant Click below to watch the Visual Concept. Visual Concept

13. Section 3 Conservation ofEnergy Chapter 5 Conserved Quantities • When we say that something isconserved,we mean that it remains constant.

14. Section 3 Conservation ofEnergy Chapter 5 Mechanical Energy • Mechanical energyis the sum of kinetic energy and all forms of potential energy associated with an object or group of objects. ME = KE + ∑PE • Mechanical energy is often conserved. MEi = MEf initial mechanical energy = final mechanical energy (in the absence of friction)

15. Section 3 Conservation of Energy Chapter 5 Conservation of Mechanical Energy Click below to watch the Visual Concept. Visual Concept

16. Section 3 Conservation ofEnergy Chapter 5 Mechanical Energy, continued • Mechanical Energy is not conserved in the presence of friction. • As a sanding block slides on a piece of wood, energy (in the form of heat) is dissipated into the block and surface.

17. Chapter 5 Section 4 Power Rate of Energy Transfer • Poweris a quantity that measures the rate at which work is done or energy is transformed. P = W/∆t power = work ÷ time interval • An alternate equation for power in terms of force and speed is P = Fv power = force  speed

18. Chapter 5 Section 4 Power Power Click below to watch the Visual Concept. Visual Concept