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The force applied to the outer surface of each wheel must also beequal otherwise one of them would be accelerating more rapidly than the other, and again the teeth of the otherwheel would break. However, the forces the forces applied tothe axles are not equal. Returning to the concept of levers, we know that the distance from the fulcrum at which theforce is applied effects the force applied at another point, and a wheel and axle works like a lever. Equal forces are being applied toeach wheel, but on the larger wheel that force is being applied at a greater distance from the axle. Thus, for the larger wheel,the force on the axle is greater than the force on the axle of the smaller wheel.

Cams and cranks

Both cams and cranks are useful when a repetitive motion is desired. Cams make rotary motion a little more interesting by essentially moving theaxle off-center. Cams are often used in conjunction with a rod. One end of the rod is held flush against the cam by aspring. As the cam rotates the rod remains stationary until the "bump" of the cam pushes the rod away from the cam'saxle. Cams can be used to create either a linear repetitive motion such as the oneillustrated in , or a repetitive rotational motion such as using a cam and a rubber band .

Cams and Cranks

Cranks convert rotary motion into a piston-like linear motion. The best examples of cranks inaction are the drive mechanism for a steam locomotive and the automobile engine crankshaft. In a crank, the wheel rotatesabout a centered axle, while an arm is attached to the wheel with an off-centered peg. This arm is attached to a rod fixedin a linear path. A crank will cause the rod to move back and forth. If instead the rod is pushed back and forth, it will causethe crank to turn. On the other hand, cams can move their rods, but rods cannot move the cams.



Pulleys can be used to simply change the direction of an applied force or to provide aforce/distance tradeoff in addition to a directional change, as shown in . Pulleys are very flexible because they use ropes or chain to transfer force rather than a rigidobject such as a rod. Ropes can be routed through virtually any path. They are able to abruptly changedirections in three-dimensions without consequence, except, of course, additional friction. Ropes canbe wrapped around a motor's shaft and either wound up or let out as the motor turns.

How Compound Pulleys Work

illustrates how a compound pulley 'trades' force for distance through anaction/reaction force pair. In a double pulley, as the rope passes over the pulley the force is transmitted entirely butthe direction has changed. The effort is now pulling up on the left side of the bottom pulley. Now, for a moment forget thatthe end of the rope is tied to the bottom of the top pulley. The mechanics are the same if the rope is fixed to theceiling. The important thing is that the end of the rope is immobile. The effort is once again transmitted entirely as therope passes over the bottom pulley and there is a direction change. The end of the rope is attached to the ceiling so therope is pulling down on the ceiling with the force of the effort (and half of the force of the load). We assume that theceiling holds up, so this must mean that there is a force balancing out this downward force. The ceiling pulls up on therope as a reaction force. This upward force is equal to the effort and now there is an upward force on the right side ofthe bottom pulley. From the perspective of a free-body diagram the compound pulley system could be replaced by tying tworopes to the load and pulling up on each with a force equal to the effort.

The disadvantages of pulleys, in contrast to machines that use rigid objects to transfer force, areslipping and stretching. A rope will permanently stretch under tension, which may affect the future performance of adevice. If a line becomes slack, then the operation of a machine may change entirely. Also, ropes will slip and stickalong pulley wheels just like belts. One solution to the problems associated with rope is to use chain. Chain ispliable like rope, and is able to transfer force through many direction changes, but the chain links are inflexible intension, so that the chain will not stretch. Chains may also be made to fit on gears so that slipping is avoided.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Notes on basic mechanics for rice elec 201. OpenStax CNX. Jun 12, 2006 Download for free at http://cnx.org/content/col10357/1.1
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