Simple machines have been around for millennia. Having first been proposed by the Greek philosopher Archimedes, they have been used by ancient civilizations in building everything from pyramids to irrigation systems [1]. As defined by NASA, simple machines are devices that are used to help complete a task by changing the direction of motion or the amount of required force [2]. In doing this, they allow for less effort to overcome a larger load, gaining what we call mechanical advantage, which is the ratio of the power output to the power input [3]. Today, ‘simple machine’ refers to the six classical simple machines that were defined by scientists during the Renaissance.
Lever:
A lever consists of a rigid bar pivoting on a fixed point called the fulcrum [4]. These devices are grouped into three classes based on fulcrum location, effort or input force, and resistance, also known as the load. Levers with the fulcrum located between the effort and the resistance are categorized as Class I, and they allow the direction of the force to be changed, which is useful for a task that requires balancing and lifting. An example would be a seesaw, where the beam is balanced on a pivot point (fulcrum) that is between a person on each end (one side is effort, the other is resistance) [4]. Class II levers are those that have the resistance located between the effort and the fulcrum, such as a wheelbarrow, where the load (dirt, rocks, etc.) is positioned between the wheel’s axle (fulcrum) and the handles (effort). Class II levers will always have a mechanical advantage and are helpful in lifting heavy objects easily. Levers in Class III have the effort located between the resistance and the fulcrum, one of which includes tongs, where the squeezing the arms (effort) is located between the pivot (fulcrum) and the food (load). These levers are good at achieving distance and generating velocity (sacrificing force for speed because of the location of the effort), which is good for quick movements [5]. Each type of lever has its own advantages, and one might be preferred over the other two to complete specific tasks [4].
Wheel and Axle:
A wheel and axle consists of a wheel attached to a smaller axle where both parts rotate together [6]. This simple machine can also be seen as a version of a lever since a force is applied to the center of the wheel, the fulcrum, through the axle. Wheel and axles are used for tasks that involve transferring rotational force, or torque, to make things easier to roll by using mechanical advantage. One example of this is a car’s steering wheel, where the force of the wheel rotating the smaller steering shaft (axle) is amplifying the driver’s applied force, allowing the wheels to turn without much effort from the driver [7].
Pulley:
A pulley consists of a wheel on an axle with a taut cable that passes over the wheel and moves and changes its rotating direction, transferring power between it and the axle [8]. There are three different types of pulley systems: fixed, movable, and compound. The simplest one is a fixed pulley, which is secured to one spot and has the wheel rotating about the axle with the rope moving over the wheel. These types of pulley systems are useful in construction sites, assisting in lifting heavy objects and changing their direction with minimal effort from people [9]. Another type of pulley is the movable pulley. It does not remain fixed and is attached to the load, which is suitable for when the load is below the person lifting. They are essential in construction and are found in construction cranes that lift heavy loads with precise control [10]. Lastly, the compound pulley is a combination of the fixed and movable pulleys. The load is on a wheel of a movable pulley, which is then attached to the rope of a fixed pulley [11].
Inclined plane:
An inclined plane consists of a sloping surface without any moving parts [12]. They are used to raise heavy objects against gravity without requiring them to directly go up vertically. An example of an inclined plane is a ramp, which can help to transport carts or other wheeled objects between two surfaces on different levels. The steepest vehicular incline in the world is the Johnstown Inclined Plane, located in Pennsylvania and originally built to transport residents up a hill with a grade of 70.9% whenever devastating floods occurred [13].
Wedge:
A wedge can be described as a triangular shape that starts thick at one end and tapers off to a thin sharp edge at the other side, and it consists of either one or two inclined planes put together [14]. There are two different types of wedges - single and double wedges. A single wedge only has one inclined plane, such as a chisel, while a double chisel has two inclined planes, such as an axe. The sharper and thinner the wedge is, the greater its mechanical advantage for splitting objects [15]. A wedge is used by applying force to the blunt end while lining up the sharp end perpendicular to the object’s slope, allowing the wedge to split the object in half.
Screw:
A screw consists of a twisted inclined plane that is wrapped around a cylinder with ridges in between [16]. Most have a sharp tip at the end to help the screw drill into tough materials like wood and plastic. However, some screws, called bolts, have smooth ends and use a nut to hold the pieces together. An example of a screw is a jar lid, where the ridges (incline plane) help secure it onto the jar.
Conclusion:
Simple machines are crucial to society by making work easier with mechanical advantage, enabling people and nations all over the world to accomplish their own monumental feats that would later become signs of their wealth and influence. Originating from basic sticks and stones, simple machines have come to affect varying fields of study and equipment with their efficiency and amplification of forces. They form the foundation of modern engineering and will continue to evolve to be incorporated into modern technology.