Chapter 9Chapter 9

Work and Work and EnergyEnergy

9.1 Work and Power9.1 Work and PowerWorkWork- a quantity that measures the effects - a quantity that measures the effects

of a force acting over a distance.of a force acting over a distance.

WW=f x d=f x d

Measured (SI) in joulesMeasured (SI) in joules

PowerPower- a quantity that measures the rate - a quantity that measures the rate at which work is done.at which work is done.

P=P=WW/t/t

Measured (SI) in Measured (SI) in watts watts (W)(W)

Simple Machine- Simple Machine- aa simple device for altering the magnitude or direction of a force.

lever, inclined plane

Compound machine- Compound machine-

machine made of more than one simple machine made of more than one simple machine. machine.

scissors, car jacks, & bicycle.scissors, car jacks, & bicycle.

Complex machine- Complex machine-

machine made of more than one compound machine made of more than one compound machine. machine.

car, tractor, etc…car, tractor, etc…

9.2 Simple Machines9.2 Simple MachinesThe Lever FamilyThe Lever Family

simple lever- hammer, crowbar, broom, etc…simple lever- hammer, crowbar, broom, etc…

divided into three classes: 1divided into three classes: 1stst, 2, 2ndnd, & 3, & 3rdrd..

All levers have a rigid All levers have a rigid armarm that turns that turns

around a point called the around a point called the fulcrumfulcrum..

pulley- modified lever. pulley- modified lever.

fixed, moveable, block & tacklefixed, moveable, block & tackle

wheel & axle- pulley connected to a shaft.wheel & axle- pulley connected to a shaft.

screwdriver & steering wheelsscrewdriver & steering wheels

The inclined plane familyThe inclined plane family Ramps- multiply and redirect the Ramps- multiply and redirect the

force.force. roads, loading docks, etc…roads, loading docks, etc…

Wedge- modified incline plane, two Wedge- modified incline plane, two inclined planes back to back. inclined planes back to back.

axe, knife, & nails.axe, knife, & nails.

Screw- inclined plane wrapped Screw- inclined plane wrapped aroundaround

a cylinder. a cylinder. bolts, jar lids, & spiral stairs.bolts, jar lids, & spiral stairs.

MachinesMachines- multiply and redirect forces - multiply and redirect forces to make work easier.to make work easier.

Mechanical advantage-Mechanical advantage- a quantity that a quantity that measures how much a machine measures how much a machine multiplies force or distance.multiplies force or distance.

MA= of/if or MA= id/odMA= of/if or MA= id/od

9.3 What is Energy?9.3 What is Energy?EnergyEnergy- the ability to do work.- the ability to do work. measured in Joulesmeasured in Joules

Potential energy-Potential energy- the stored energy the stored energy resulting from the relative positions resulting from the relative positions of objects in a system. of objects in a system.

Chemical energyChemical energyElastic potential energyElastic potential energyGravitational potential Gravitational potential

energyenergyPE= mghPE= mgh

Kinetic energy- Kinetic energy- the energy of a moving the energy of a moving object due to its motion.object due to its motion.

depends on mass but more on depends on mass but more on speed.speed.

KE=KE=½mv²½mv²

Mechanical energy- Mechanical energy- the sum of the the sum of the kinetic and potential energy of large-kinetic and potential energy of large-scale objects in a system.scale objects in a system.

Non mechanical energy-Non mechanical energy- energy at the energy at the level of atoms that does not affect level of atoms that does not affect motion on a large scale.motion on a large scale.

Solar energy- Solar energy- energy from the sun.energy from the sun.

Electrical energy- Electrical energy- charged particles charged particles (electrons) flowing through wires or (electrons) flowing through wires or other conducting materials.other conducting materials.

Light energy- Light energy- electromagnetic waves.electromagnetic waves.

Potential and Kinetic EnergyPotential and Kinetic Energy

9.4 Conservation of Energy9.4 Conservation of Energy

Energy transformations- changing from Energy transformations- changing from one form of energy to another form.one form of energy to another form.

KEKE PE thrown ball at it’s PE thrown ball at it’s apexapex

PEPE KE apple falling from KE apple falling from treetree

Chemical Chemical KE fire cracker KE fire cracker

Law of Conservation of Energy- energy Law of Conservation of Energy- energy cannot be created or destroyedcannot be created or destroyed

Energy Transformations Energy Transformations

Efficiency of MachinesEfficiency of Machines

* not all work done by a machine is * not all work done by a machine is useful work. Lose some due to useful work. Lose some due to

frictionfriction

and other factors.and other factors.

Efficiency- Efficiency- a quantity that measures the a quantity that measures the ratio of useful work output to work ratio of useful work output to work input, usually expressed as a input, usually expressed as a percentage.percentage.

efficiency efficiency = = useful work outputuseful work output

work inputwork input

efficiencyefficiency

Law of conservation of energyLaw of conservation of energy