Work, Power and Energy Chp 10 and 11. Some Terms Work Exerting a force over a distance Energy ...
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Transcript of Work, Power and Energy Chp 10 and 11. Some Terms Work Exerting a force over a distance Energy ...
Work, Power and Work, Power and EnergyEnergyChp 10 and 11Chp 10 and 11
Some TermsSome Terms WorkWork
Exerting a force over a distanceExerting a force over a distance EnergyEnergy
The ability to do work (or change the world around you)The ability to do work (or change the world around you) Kinetic energyKinetic energy
Energy due to motionEnergy due to motion Potential energyPotential energy
Energy due to position or compositionEnergy due to position or composition Work-energy theoremWork-energy theorem
work is required to change KEwork is required to change KE
PowerPower The rate at which work is doneThe rate at which work is done
WorkWork
Must be exerted over a distanceMust be exerted over a distance If nothing moves, no work was done on THAT object If nothing moves, no work was done on THAT object
(could still be done on you)(could still be done on you) Need to use the net force to calculate workNeed to use the net force to calculate work
All the vector addition rules still applyAll the vector addition rules still apply SI unit is Joule (J)SI unit is Joule (J) Work is a vector, since force and displacement are Work is a vector, since force and displacement are
vectorsvectors Can be negative, which means the work is being done by Can be negative, which means the work is being done by
the object rather than on itthe object rather than on it
PowerPower
If the same amount of If the same amount of work is done more work is done more quickly, then more power quickly, then more power is exertedis exerted Its harder to do a job Its harder to do a job
quickly than it is to do the quickly than it is to do the same job more slowlysame job more slowly
SI unit is Watts (W)SI unit is Watts (W) Often we use kilowatts Often we use kilowatts
since watts are such a since watts are such a small unitsmall unit
Simple MachinesSimple Machines
A device that makes work A device that makes work easier, either by changing easier, either by changing the distance or direction the distance or direction that a force is exertedthat a force is exerted It doesn’t make the work It doesn’t make the work
lessless If you increase the distance If you increase the distance
a force is exerted, than less a force is exerted, than less force is needed to do the force is needed to do the same amount of worksame amount of work
The machine imparts no The machine imparts no energy of its ownenergy of its own
6 Types of Simple 6 Types of Simple MachinesMachines
Inclined planeInclined plane Ex. rampEx. ramp
LeverLever Ex. crowbarEx. crowbar
Wheel and axelWheel and axel Ex. tireEx. tire
PulleyPulley Ex. Well bucketEx. Well bucket
WedgeWedge Ex. axEx. ax
Screw Screw Ex. Wood screw Ex. Wood screw
Calculating the Benefits Calculating the Benefits of Machinesof Machines
Mechanical advantageMechanical advantage Compares effort and resistance forcesCompares effort and resistance forces
Ideal mechanical advantageIdeal mechanical advantage Compares effort and resistance distancesCompares effort and resistance distances
Efficiency Efficiency Compares how much of the input work gets Compares how much of the input work gets
translated to output worktranslated to output work Often work is lost to heat due to frictionOften work is lost to heat due to friction
Compound MachinesCompound Machines
Result from a combination of 2 or more Result from a combination of 2 or more simple machinessimple machines
The resistance force of one machine The resistance force of one machine becomes the effort force of anotherbecomes the effort force of another Like dominoesLike dominoes
However, the efficiency is less because However, the efficiency is less because friction increases with each additional friction increases with each additional machinemachine
Conservation of EnergyConservation of Energy
Energy can change forms and be passed Energy can change forms and be passed between objects, but it cannot be created between objects, but it cannot be created or destroyedor destroyed
Forms of energy:Forms of energy: KineticKinetic Elastic potential energyElastic potential energy Thermal energyThermal energy Gravitational potential energyGravitational potential energy
CollisionsCollisions
2 types:2 types: ElasticElastic
KE is conserved in the KE is conserved in the collisioncollision
Occurs between hard objectsOccurs between hard objects Inelastic Inelastic
KE is lost in the collision due KE is lost in the collision due to deformation, heat and to deformation, heat and soundsound
Occurs between soft or sticky Occurs between soft or sticky objectsobjects
Energy is still conserved, Energy is still conserved, its just not all kept at KEits just not all kept at KE