Chapter 5 Work and energy

Introduction Energy present in many forms in universe Mechanical, chemical, electromagnetic, nuclear The total energy in the universe remains constant…Law of conservation of energy Energy can only change forms, can’t be created or destroyed Work is the link between concept of froce and energy

5.1 Work Work occurs when a force is applied to an object over a distance and the object moves It must move in the direction of the applied force It must move

5.1 Work Work is a scalar quantity Units are joules: Newton-meter Work makes you “mad”

5.2 Kinetic Energy Kinetic Energy: energy of motion Has same units as work (joules)

5.2 Kinetic Energy Known as the “work energy theorem” Work done on an object is equal to change in its kinetic energy If positive, work goes into the system If negative, work comes out of the system

5.3 Potential Energy Potential energy is the energy of “position” Aka Gravitational Potential energy Same units as work…joules

5.4 Conservative and Nonconservative Forces Conservative forces: the work done on an object does not depend on the path E.g. the force of gravity Nonconservative forces lead to lost energy E.g Friction

5.5 Conservation of Mechanical Energy When a physical quantity is conserved, the value of the quantity remains constant If objects are effected only by conservative forces, then total mechanical energy will remain constant

5.5 Conservation of Mechanical Energy Hook’s Law describes the energy stored in a spring Elastic Potential energy

5.6 Nonconservative Forces The work done by all nonconservative forces is equal to the change in mechanical energy

5.8 Power Power is the time rate of doing work If work makes you “mad”, power is “how long” you are mad Measured in “watts”