2 Work and PowerWork- a quantity that measures the effects of a force acting over a distance.W=f x dMeasured (SI) in joulesPower- a quantity that measures the rate at which work is done.P=W/tMeasured (SI) in watts (W)
3 Simple Machine- a simple device for altering the magnitude or direction of a force. lever, inclined planeCompound 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…
4 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 turnsaround a point called the fulcrum.pulley- modified lever.fixed, moveable, block & tacklewheel & axle- pulley connected to a shaft.screwdriver & steering wheels
5 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 arounda cylinder.bolts, jar lids, & spiral stairs.
6 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
7 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 energyElastic potential energyGravitational potential energyPE= mgh
8 Kinetic energy- the energy of a moving object due to its motion. depends on mass but more on speed.KE=½mv²Mechanical 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.
9 Solar energy- energy from the sun. Electrical energy- charged particles (electrons) flowing through wires or other conducting materials.Light energy- electromagnetic waves.
11 9.4 Conservation of Energy Energy transformations- changing from one form of energy to another form.KE PE thrown ball at it’s apexPE KE apple falling from treeChemical KE fire crackerLaw of Conservation of Energy- energy cannot be created or destroyed
13 Efficiency of Machines * not all work done by a machine is useful work. Lose some due to frictionand other factors.Efficiency- a quantity that measures the ratio of useful work output to work input, usually expressed as a percentage.efficiency = useful work outputwork input