Understanding Mechanical Systems: Levers, Pulleys, and Gears

Mechanisms

Mechanisms are components used to transmit or transform movement. They can transmit linear motion, used for raising objects, or circular motion, used to change speed.

Levers

A lever is a rigid bar that pivots around a fixed point called a fulcrum. One end of the lever applies a force, while the other end moves a resistance.

Types of Levers

Depending on the positions of the fulcrum, force, and resistance, there are three types of levers:

• First-Class Lever

  The fulcrum is located between the force and the resistance. Example: Scissors, which are essentially two first-class levers joined together.

• Second-Class Lever

  The resistance is located between the fulcrum and the force. Example: Wheelbarrows.

• Third-Class Lever

  The force is located between the fulcrum and the resistance. Examples: Tweezers, pliers, or ice tongs.

Law of the Lever

The Law of the Lever states that the force multiplied by its distance from the fulcrum equals the resistance multiplied by its distance from the fulcrum. These distances are often referred to as lever arms.

Pulleys

• Fixed Pulley

  A fixed pulley is a wheel with a fixed axis. It has a groove around its circumference to hold a rope, belt, or chain.

• Movable Pulley

  In a movable pulley, the weight is attached to the pulley's axle. The force required to lift the weight is equal to half the resistance.

• Pulley System (Block and Tackle)

  A combination of fixed and movable pulleys, where the force required to lift a load is reduced by half for each additional movable pulley.

Gears

A gear is a wheel with teeth on its outer edge that allows it to transmit motion to another gear.

The gear that provides the motion is called the driving gear, and the gear that receives the motion is called the driven gear.

The number of revolutions per minute (rpm) is used to measure the rotational speed of a gear. It represents the number of complete rotations a gear makes in one minute.

The letter z represents the number of teeth on a gear, and N represents the number of revolutions per minute.

Transmission Ratio

The transmission ratio is the relationship between the number of revolutions of the driving gear and the number of revolutions of the driven gear.

Chain and Gear System

In this system, motion is transmitted from one gear to another through a chain. Both gears rotate in the same direction. The formula for this mechanism is the same as for direct gears.

Worm Gear

A worm gear consists of a screw with a single continuous groove, effectively having only one tooth. The screw meshes with a gear whose axis is perpendicular to the screw's axis. Only the screw can drive the gear; the gear cannot drive the screw. The screw is therefore the driving element.

Sheaves with Belts

Two pulleys connected by a belt. The belt may slip, meaning it might not transmit motion if one of the pulleys is locked.

Where D is the diameter and N is the number of revolutions. If the belt is crossed, the pulleys will rotate in opposite directions.