Wheel and axle

The wheel is one of the most significant inventions in the history of the world. Before the invention of wheels, the amount of load and the distance through which we could carry the load over land was limited. 

Wheeled carts facilitated agriculture and commerce by enabling the transportation of goods to and from markets, as well as easing the burdens of people traveling great distances.

Wheel and axle make work easier by moving objects across distances. The wheel and axle greatly reduce the friction involved in moving an object. The wheel (round ends) turns with the axle (or cylindrical post), causing movement. 

In addition to reducing friction, a wheel and axle can also serve as a force multiplier. If a wheel is attached to an axle, and a force is used to turn the wheel, the rotational force, or torque, on the axle is much greater than the force applied to the rim of the wheel. 

The wheel and axle is a type of simple machine used to make tasks easier in terms of manipulating force by applying mechanical advantage. The system changes the force by changing the distance over which the force must be applied, if the input force is reduced to \[1/5\] the output force, then the force must be applied over five times the distance.

The wheel and axle both rotate at the same rate. What this means is that both the axle and the wheel will complete one full rotation in the same amount of time. Due to the size difference in the radius of the wheel and axle, this means that the distance the two parts rotate through in the same amount of time is different. This is due to the difference in the circumferences of the wheel itself and the axle that supports it. This supplies the conditions for mechanical advantage.

The mechanical advantage for this system is ideally:

IMA=Rr

where R is the radius of the wheel, and r is the radius of the axle, shown in the diagram below:

A wheel and axle system need a force in order to lift the load, but that force can be less than the weight of the object. Although the force a person needs to apply may not be very large compared to the force it does on the object, the distance they need to rotate the wheel is much larger than the distance the axle rotates through.

Examples of wheel and axle machines

1. Bicycle 

A bicycle consists of an arrangement of wheel and axle that helps it move forward. Here, the force applied to the axle initiates the motion and causes the wheels of the cycle to move.

2. Car Tyres

The tyres of a car move forward or turn to either side with the help of an axle. When the engine of the car exerts a force on the axle, the wheels tend to move or rotate accordingly.

3. A Ferris Wheel consists of a giant wheel that rotates in a circular direction. The centre point of the Ferris wheel consists of a cylindrical rod known as the axle. The axle is subjected to a high magnitude electrical force, which supports the rotation of the Ferris wheel.

4. A doorknob closely resembles the wheel and axle simple machine. Here, the doorknob acts as the wheel, and the shaft present at the centre of the knob functions as the axle. When the knob is turned, a force is built on the shaft or the axle. This force helps retract the latch and open or close the door with ease.