Introduction


Wheel and Axle

Wheel and Axle, simple machine, consisting of a circular objectthe wheelwith a shaftthe axlerunning through and attached to the center of the wheel. A round doorknob and a round water faucet are both examples of wheels and axles. The much larger handle turns a much smaller axle to move a door latch, in the case of a doorknob, or open a water valve, in the case of a faucet. The wheel and axle is used to make doing a given amount of work easier. Work is the result of a physical force, such as the effort of pushing or pulling, that moves an object over a distance. A wheel and axle makes work easier by changing the amount and direction of the force applied to move (or in this case, turn) an object. The object to be moved is a resistance, or load, located at the axle. A force applied at the outer edge of the wheel moves or turns the load located at the axle. The wheel enables a user to apply the force over a greater distance than would be possible if the force were applied directly to the axle. In this way, a wheel and axle reduces the effort needed to move a load.

The wheel and axle is one of the four simple

The wheel and axle is one of the four simple machines (along with the lever, the pulley, and the inclined plane). All simple machines change the amount of effort needed to do work, and are the basis for all other machines. Another common example of a wheel and axle is the steering wheel of a car, where the driver exerts a force on the outer edge of the wheel to cause the load at the axle (the front wheels) to turn.

Work and Mechanical Advantage



A wheel and axle makes work easier by changing

A wheel and axle makes work easier by changing the amount of force applied to a load. Work, in physics, is defined as the amount of force applied to an object multiplied by the distance over which that force is applied. Mathematically, the formula to compute work can be expressed as:
=== ===
Work = Force Distance

For a wheel and axle

For a wheel and axle, the work to be done is the moving or turning of a load, usually located at the axle. The force needed is the effort required to turn the load, and the distance corresponds to how far the wheel is turned as effort is applied. Because the circumference of the wheel is always larger than the circumference of the axle, any effort applied to the wheel will always move a greater distance than the load at the axle. The wheel and axle makes the effort move a greater distance than the load, and so less effort is needed to move the load.

The mechanical advantage (MA) of a wheel

The mechanical advantage (MA) of a wheel and axle measures how much the machine multiplies the force applied by the user. There are two kinds of MA: theoretical and actual. Theoretical MA is the MA that would exist if the machine were perfect, but all machines lose some of their MA to friction. Friction is a resistance created between objects when they move against each other. Friction makes the process of moving objects, and therefore doing work, more difficult. Theoretical MA is the one most commonly referred to, since actual MA can be difficult to calculate.

To find the MA of a simple machine

To find the MA of a simple machine, the distance the effort travels is divided by the distance the load travels. If force is applied to the wheel, then the MA of a wheel and axle equals the radius of the wheel divided by the radius of the axle. This will always produce an MA greater than 1, since the force will always travel a greater distance on the larger wheel than will the load at the smaller axle. A screwdriver is a type of wheel and axle. The wheel (the handle) transmits the user`s force to the axle (the screwdriver shaft) to turn a screw. Turning the larger handle of the screwdriver is much easier than trying to turn the smaller screw by itself. The mechanical advantage of this type of wheel and axle can be very large.

In the previous examples

In the previous examples, force applied at the wheel moved a heavy load at the axle. Force can also be applied at the axle to move a load at the wheel. This requires more force to move the wheel, but one benefit is that the wheel will move much faster. When force is applied at the axle, the MA is the radius of the axle divided by the radius of the wheel. This produces a MA less than 1, and means that speed will be gained. Wheels and axles used in this fashion often obtain force generated by fuel-powered engines. The large blades of an airplane propeller move much faster than the small axle in the middle, but it takes the power of an engine to turn the axle.

If a wheel can rotate independently about

If a wheel can rotate independently about the axle, then the device is not a true machine, because it does not change force. However, freely rotating wheels and axles are used frequently to reduce friction. Rolling is easier than pushing or dragging an object.

Wheel and Axle Applications


Wheels and axles are used in one form or

Wheels and axles are used in one form or another in most complex machines. Gears, such as those used in a mechanical clock, are actually wheels with teeth around the edge. When one gear turns, the other gear turns in the opposite direction. If the gears are the same size, they turn at the same speed. However, if one gear is larger than the other, the smaller gear turns faster than the larger gear.

Wheel and axle combinations also can be

Wheel and axle combinations also can be used with belts or chains (as on a bicycle) to transmit the forces from one wheel to the other. A wheel that drives or is driven by a chain is usually referred to as a sprocket. Belts, closed loops of rope or rubber, are often used in automobiles to transmit the rotary power from the engine to fans or other devices.

Wheels and axles are also used to change

Wheels and axles are also used to change the direction of applied force. The back and forth motion (called reciprocating motion) of a piston in an engine can be changed into rotary motion by connecting the piston to the edge of a wheel. The drive wheels of an old-fashioned steam locomotive operate in this way. The pistons in an automobile engine are connected to a crankshaft, a special type of axle that provides the rotary motion to the wheels of a car. The process is also used in reverse so rotary motion can be changed to reciprocating motion. This method is used to convert the rotary motion of an electric motor into the up-and-down motion of a jigsaw blade or a sewing-machine needle.

History


Wheels and axles have been used for centuries

Wheels and axles have been used for centuries to magnify force. The use of wheels to reduce friction while moving objects was one of the most important inventions in human civilization, because it made transportation much easier. Wheels used for transportation are believed to have been used on carts in Mesopotamia as early as 3500 bc.

One of the first uses of the wheel as a

One of the first uses of the wheel as a tool was the potter`s wheel, usually made of stone and used to make pottery. It was invented about the same time as the wheel used in transportation. A likely early use of the fixed wheel and axle to multiply force was the winch, which can be used with a rope to pull heavy objects with less effort. A small force applied at the outer edge of a winch handle is changed into a large force at the axle. Winches can be used to haul heavy buckets of water up from wells, or move other large objects. Windmills and waterwheels (both forms of wheel and axle) were combined with gearing to make mills for grinding grain. The wrench uses the principle of the wheel and axle to turn screws or tighten bolts. Most mechanical devices make some use of the wheel and axle.

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