Chapter 9 Work and Energy

9.1 Work and Power Work- a quantity that measures the effects of a force acting over a distance. W=f x d Measured (SI) in joules Power- a quantity that measures the rate at which work is done. P=W/t Measured (SI) in watts (W)

Simple Machine- a simple device for altering the magnitude or direction of a force. lever, inclined plane Compound machine- machine made of more than one simple machine. scissors, car jacks, & bicycle. Complex machine- machine made of more than one compound machine. car, tractor, etc…

9.2 Simple Machines The Lever Family simple lever- hammer, crowbar, broom, etc… divided into three classes: 1st, 2nd, & 3rd. All levers have a rigid arm that turns around a point called the fulcrum. pulley- modified lever. fixed, moveable, block & tackle wheel & axle- pulley connected to a shaft. screwdriver & steering wheels

The inclined plane family Ramps- multiply and redirect the force. roads, loading docks, etc… Wedge- modified incline plane, two inclined planes back to back. axe, knife, & nails. Screw- inclined plane wrapped around a cylinder. bolts, jar lids, & spiral stairs.

Machines- multiply and redirect forces to make work easier. Mechanical advantage- a quantity that measures how much a machine multiplies force or distance. MA= of/if or MA= id/od

9.3 What is Energy? Energy- the ability to do work. measured in Joules Potential energy- the stored energy resulting from the relative positions of objects in a system. Chemical energy Elastic potential energy Gravitational potential energy PE= mgh

Kinetic energy- the energy of a moving object due to its motion. depends on mass but more on speed. KE=½mv² Mechanical energy- the sum of the kinetic and potential energy of large-scale objects in a system. Non mechanical energy- energy at the level of atoms that does not affect motion on a large scale.

Solar energy- energy from the sun. Electrical energy- charged particles (electrons) flowing through wires or other conducting materials. Light energy- electromagnetic waves.

Potential and Kinetic Energy

9.4 Conservation of Energy Energy transformations- changing from one form of energy to another form. KE PE thrown ball at it’s apex PE KE apple falling from tree Chemical  KE fire cracker Law of Conservation of Energy- energy cannot be created or destroyed

Energy Transformations

Efficiency of Machines * not all work done by a machine is useful work. Lose some due to friction and other factors. Efficiency- a quantity that measures the ratio of useful work output to work input, usually expressed as a percentage. efficiency = useful work output work input

efficiency

Law of conservation of energy