2.
WORKWORK
The transfer ofThe transfer of
energy that occursenergy that occurs
when a force makeswhen a force makes
an object movean object move
In order forIn order for workwork toto
be done a force mustbe done a force must
make an objectmake an object movemove
3.
2 Conditions of work2 Conditions of work
1. The object1. The object must movemust move
2. Movement must be in the2. Movement must be in the same directionsame direction asas
the force appliedthe force applied
4.
Work and EnergyWork and Energy
When work is done there is always a transferWhen work is done there is always a transfer
of energyof energy
Energy is the ability to do workEnergy is the ability to do work
When you do work on an object, you increaseWhen you do work on an object, you increase
its energyits energy
5.
Calculating workCalculating work
Work (J) = Force (N) x distance (m)Work (J) = Force (N) x distance (m)
W = FdW = Fd
6.
PowerPower
The rate at which work is doneThe rate at which work is done
SI unit for power is theSI unit for power is the Watt (W)Watt (W)
P (watts) = Work (J)/Time (s)P (watts) = Work (J)/Time (s)
Usually expressed in kilowattsUsually expressed in kilowatts
7.
Power and EnergyPower and Energy
Power is the rate at which energy is transferredPower is the rate at which energy is transferred
Power (w) = energy (J)/Time (s)Power (w) = energy (J)/Time (s)
8.
MachineMachine
A device that makes doing work easierA device that makes doing work easier
9.
Simple MachinesSimple Machines
A Machine that doesA Machine that does
work with onlywork with only oneone
movementmovement of theof the
machinemachine
6 types6 types of simpleof simple
machines: lever, pulley,machines: lever, pulley,
wheel and axle, inclinedwheel and axle, inclined
plane, screw, and wedgeplane, screw, and wedge
10.
LeverLever
A bar that is freeA bar that is free
to pivot or turnto pivot or turn
around a fixedaround a fixed
pointpoint
The fixed point isThe fixed point is
called a fulcrumcalled a fulcrum
There are 3There are 3
classes of leversclasses of levers
11.
PulleyPulley
A grooved wheel with aA grooved wheel with a
rope, chain, or cablerope, chain, or cable
running along therunning along the
groovegroove
The axle of the pulleyThe axle of the pulley
acts as the fulcrumacts as the fulcrum
Fixed and movableFixed and movable
Fixed IMA = 1,Fixed IMA = 1,
Movable IMA = 2Movable IMA = 2
12.
Block and Tackle pulleyBlock and Tackle pulley
A system of pulleysA system of pulleys
consisting of bothconsisting of both fixedfixed
and movableand movable pulleyspulleys
IMA is equal to theIMA is equal to the
number of ropenumber of rope
segmentssegments that supportthat support
the weightthe weight
13.
Wheel and AxleWheel and Axle
consists of a shaft orconsists of a shaft or
axle attached to a largeraxle attached to a larger
wheel.wheel.
The wheel and axleThe wheel and axle
rotate togetherrotate together
Examples:Examples: PencilPencil
sharpeners, door knobs,sharpeners, door knobs,
screw drivers, faucetscrew drivers, faucet
handleshandles
14.
Inclined PlaneInclined Plane
A sloping surface, suchA sloping surface, such
as a ramp.as a ramp.
Reduces the amount ofReduces the amount of
force required to doforce required to do
workwork
IMA = Length of slopeIMA = Length of slope
(m)/Height (m)(m)/Height (m)
15.
ScrewScrew
An inclined planeAn inclined plane
wrapped in a spiralwrapped in a spiral
around a cylindricalaround a cylindrical
postpost
IMA is related to theIMA is related to the
spacing of the threadsspacing of the threads
16.
WedgeWedge
AnAn inclined planeinclined plane withwith
one or two sloping sidesone or two sloping sides
ItIt changes the directionchanges the direction
of theof the input forcesinput forces
17.
Compound MachineCompound Machine
Two or moreTwo or more simple machines that operatesimple machines that operate
togethertogether
A car is a compound machineA car is a compound machine
19.
2-Forces Involved in Work2-Forces Involved in Work
11.. Input Force:Input Force: The force that is applied to theThe force that is applied to the
machine. (effort force)machine. (effort force)
Given the symbolGiven the symbol FFinin
2.2. Output Force:Output Force: The force applied by theThe force applied by the
machine.machine.
Given the symbolGiven the symbol FFoutout
20.
2-Types of Work done on a Machine2-Types of Work done on a Machine
1.1. Input Work:Input Work: The work done by you on theThe work done by you on the
machine.machine.
Given the symbolGiven the symbol WWinin
2.2. Output Work:Output Work: The work done by theThe work done by the
machine.machine.
Given the symbolGiven the symbol WWoutout
21.
Conserving EnergyConserving Energy
A machineA machine cannotcannot create energy, so…create energy, so…
WWoutout cancan never benever be greater thangreater than WWinin
22.
Which means that…Which means that…
WWoutout will always bewill always be lessless thatthat WWinin ……
because friction changes some of the energybecause friction changes some of the energy
to heat.to heat.
23.
Ideal MachineIdeal Machine
A machine without friction.A machine without friction.
WWinin = W= Woutout
24.
Mechanical AdvantageMechanical Advantage
The ratio of the output force to the input force.The ratio of the output force to the input force.
Can be calculated using the following equation.Can be calculated using the following equation.
25.
EfficiencyEfficiency
A measure of how much of the input work put into aA measure of how much of the input work put into a
machine is change into useful output.machine is change into useful output.
26.
Efficiency Cont…Efficiency Cont…
• The efficiency of an ideal machine is 100
percent.
• The efficiency of a real machine is always less
than 100 percent.
27.
How can machines be made moreHow can machines be made more
efficient???efficient???
• by adding a lubricant,
such as oil or grease, to
surfaces that rub
together.
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