Mechanical Advantage

In our second learning objective, we will be introducing the concept of mechanical advantage, with emphasis on the role of pulleys, levers, and gears. Mechanical advantage is defined as the idea that machines, like pulleys, help us do more with less effort. It’s the key to lifting heavier loads or moving objects with ease. Understanding this concept is essential for maximizing efficiency in various mechanical systems such as elevators, ziplines, sailboats, etc.

Pulleys

Pulleys are simple yet powerful machines that allow us to lift or lower heavy objects with less effort. A pulley consists of a wheel with a groove around its circumference and a rope or belt that fits into the groove. When one end of the rope is pulled, it moves around the wheel, causing the object to move. Pulleys work by changing the direction or magnitude of the force needed to move an object. Instead of lifting the heavy box straight up, you can use a pulley to change the direction of the force needed to lift the box.

Types of Pulleys

Fixed Pulley

Fixed Pulley

A fixed pulley is attached to a stationary object, like a ceiling or a beam. There is no change in force, only change in its direction, it doesn’t provide any mechanical advantage.

Movable Pulley

Movable Pulley

A movable pulley is attached to the object being lifted. When you pull down on the rope, the pulley moves with the object, providing a mechanical advantage by reducing the force needed to lift the object.

Compound Pulley

Compound Pulley

A compound pulley is a combination of fixed and movable pulleys. It provides both a change in direction and a mechanical advantage, making it easier to lift heavy loads.

Challenge!

Create your own DIY pulley system using everyday materials!

Levers

A lever is a simple machine made of a rigid beam or bar that pivots on a fixed point called a fulcrum, like a seesaw. Levers are all around us and are used in many everyday objects and tools. It works by applying a small force over a large distance to lift or move a heavy object. When you push down on one end of the lever (the input force), it causes the other end to move up, lifting the load (the output force).

Fulcrum

It’s the fixed point or pivot around which the lever rotates. It’s like the center point of a seesaw where it balances.                                     

Effort Arm

The part of the lever where you apply the force (the input force) to lift or move the load. It’s the distance between the fulcrum and where you push or pull on the lever.

Load Arm

The part of the lever where the load (the output force) is located. It’s the  distance between the fulcrum and the object ­‌‍‎ being lifted or moved.        ­    

As the fulcrum gets closer to the load, the mechanical advantage increases, making the effort to lift the load much smaller. However, using the energy formula, in order for the effort to lift the load to decrease, the distance over which the force acts need to increase.

There are 3 types of levers:

The fulcrum is located between the effort arm and the load arm. This system can only be balanced if the effort is equal to the load, examples include a seesaw, scissors, pliers, etc.
In a second-class lever, the load is located between the fulcrum and the effort arm, such as a wheelbarrow or a nutcracker.
In a third-class lever, the effort arm is located between the fulcrum and the load, such as a fishing rod or a broom.

This video clearly explains the lever machine in an innovative way.

Gears

Gears are circular wheels with teeth around their edges. These teeth fit into each other like pieces of a puzzle, like the ones you see in bicycles or clocks. When one gear turns, it makes the gear next to it turn as well which transfers the motion and power from one part of a machine to another.

An important concept in gears is the gear ratio. It’s defined as the ratio of the number of teeth on the driven gear to the number of teeth on the driver gear in a gear system, it indicates how many times one gear rotates in relation to the other.

If the gear ratio is large, this means that the driven gear has more teeth than the driving gear leading to a reduction in speed but increase in torque which increases the mechanical advantage. Examples are hydraulic systems, wind turbines, conveyor systems in factories, where high strength is required. Inversely, for small gear ratios, the speed is increased while decreasing the torque, its applications can be found in clocks and bicycles where faster rotational speed is required.

Types of Gears

Spur Gear

These are the most common type of gears. They have teeth that are straight and run parallel to the gear’s axis, they are usually used in machines like cars and bicycles.

 

Rack and Pinion

These gears convert rotary motion into linear motion and vice versa. They consist of a linear gear (rack) that connects with a toothed wheel (pinion) and are commonly found in steering systems, elevators, and CNC machines.

 

Helical Gear

These gears have teeth that are angled or helical. This design makes them smoother and quieter but also stronger than spur gears. Helical gears are commonly found in industrial machines and gearboxes.

Bevel Gear

Bevel gears have cone-shaped teeth, and they are used when the direction of motion needs to be changed, they are used in hand drills to transfer motion from the handle to the drill bit.

Worm Gear

Worm gears consist of a screw-like gear (the worm) that meshes with a toothed wheel. They are used when a high gear ratio is needed, such as in conveyor belts and elevators.

Internal Gear

Internal gears have teeth cut on their inner surfaces, enabling them to mesh within the same housing, commonly used in confined spaces or specific mechanical setups.

This video clearly explains gears, gear ratio, and its various applications.

Case Study

The Great Pyramid of Giza, one of the most ancient wonders of the world that has left even modern engineers astonished, was constructed using various innovative engineering techniques. Considering the height of the pyramid, 147 meters, and the average weight of each block, 15 tons, the ancient Egyptians were believed to have utilized ramps, sledges, and pulley systems to help build this engineering marvel.

In order for the heavy blocks to be transported, wooden sledges or logs were used to transport the blocks across the desert. It was also theorized that water was used to dampen the sand and act as a lubricant to ease the journey. The blocks were placed on the sledges by a system of pulleys and ropes that help reduce the force required to lift these immensely heavy blocks, a concept known as mechanical advantage. Pulleys were also utilized to drag the blocks up the ramps; the earth ramps were used to transport the blocks up each level of the pyramid.

Quiz!

Test your knowledge by completing the quiz.

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DONE!

Congratulations on mastering the basics of mechanics! Remember, mechanics is the backbone of many disciplines, from civil engineering to aerospace. Keep your curiosity alive, continue to delve deeper into this fascinating subject, and you’ll unlock endless possibilities in your career as an engineer.
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