How do simple machines like levers, pulleys, and ramps work?
Simple machines are fundamental mechanical devices that change the direction or magnitude of a force to perform work. They are the building blocks of all complex machines and have been integral to human civilization’s technological progress. The six classical simple machines are the lever, wheel and axle, pulley, inclined plane, wedge, and screw. Here, we will focus on three: levers, pulleys, and inclined planes (or ramps).
Levers
A lever is a rigid bar or beam free to rotate around a fixed point called the fulcrum. Levers can be classified into three types: first-class, second-class, and third-class, each with different arrangements of the fulcrum, effort (input force), and load (output force or resistance).
First-class lever
The fulcrum is in the middle, with the effort on one end and the load on the other. Examples include seesaws and scissors. Here, the direction of the effort is reversed; if you push down on the lever, the load rises.
Second-class lever
The load is in the middle, between the fulcrum and the effort. Examples include wheelbarrows and nutcrackers. The direction of the effort is not reversed; pushing down on the lever raises the load.
Third-class lever
The effort is in the middle, between the load and the fulcrum. Examples include tweezers and human arms. The direction of the effort is not reversed.
The lever’s mechanical advantage (MA), or the ratio of output force to input force, is the ratio of the distances from the fulcrum to the points of application of the load and effort, respectively. Levers can multiply force (MA > 1) or distance (MA < 1), depending on their configuration.
Pulleys
A pulley is essentially a wheel on an axle designed to support movement and change of direction of a cable or belt. There are three types of pulleys: fixed, movable, and compound.
Fixed pulley
A fixed pulley changes the direction of the applied force. If you pull down on the rope, the load on the other end of the rope is lifted up. However, the force you need to apply to lift the load is the same as the weight of the load. Therefore, the mechanical advantage is 1.
Movable pulley
A movable pulley is attached to the load. Pulling down on one side of the rope results in the load being lifted. In this case, the effort needed to lift the load is half the weight of the load. Therefore, the mechanical advantage is 2.
Compound pulley
Compound pulleys, or block and tackle systems, combine fixed and movable pulleys. The mechanical advantage equals the number of sections of ropes supporting the load. They can dramatically reduce the effort needed to lift a load.
Inclined Planes (Ramps)
An inclined plane, or ramp, is a flat surface tilted at an angle, used to facilitate the raising or lowering of a load. The mechanical advantage of an inclined plane is the ratio of the length of the sloping surface (the distance the effort moves) to the height of the load (the distance the load moves), or equivalently, the reciprocal of the sine of the angle of inclination.
By increasing the slope’s length (reducing the angle of inclination), the effort needed to overcome the load’s weight is decreased. However, the effort must move over a longer distance. This trade-off is the essence of the mechanical advantage of simple machines.
Ramps are used everywhere in our daily lives, from roads and pathways to wheelchair access ramps and loading docks.
In summary, simple machines like levers, pulleys, and inclined planes work by changing the direction or magnitude of the applied force, thus making tasks easier or even possible that would otherwise be difficult or impossible. They are the essence of mechanical advantage, enabling us to do more with less effort. Despite their simplicity, these machines underpin much of the technology and infrastructure we rely on today.
