Simple Machines and Mechanisms: Levers, Pulleys, and More
Simple Machines and Mechanisms
Levers
A lever is a rigid bar that is supported by a fulcrum.
Formula: F · d = R · r
Lever Classes
- Class 1: The fulcrum is between the effort applied and the resistance. The effect of the effort applied can be multiplied or reduced.
- Class 2: The resistance is between the fulcrum and the effort applied. The effect of the effort applied is always multiplied.
- Class 3: The effort applied is between the fulcrum and the resistance. The effect of the effort applied is always reduced.
Pulleys
Fixed Pulley
A fixed pulley is a wheel that has a groove around it into which a rope, chain, or belt fits.
Movable Pulley
A movable pulley is a set of two pulleys—one is fixed while the other can move in a linear direction.
A movable pulley is balanced when F = R/2.
Compound Pulley
This is a system of fixed and movable pulleys, often called a block and tackle.
Rotary Motion Mechanisms
These mechanisms transmit motion and effort in a circular way, from the input to the output.
Mechanisms That Transform Motion
Rotary to Linear Motion
- Rack and Pinion System: This uses a pinion that is a small cogwheel, mounted on a rack that is a toothed belt or bar.
- Nut and Bolt System: This consists of a bolt or threaded bar and a nut that has the same interior diameter as the diameter of the bolt.
- Winch and Crank Handle: This is a drum that rotates and a crank handle that allows us to lift objects.
- Crank-Link-Slider: This is composed of a crank and a rod called a connecting rod or link. This rod has articulated joints at each end—one is connected to the crank and the other to the slider.
- Crankshaft: This is a set of connecting rods attached to a jointed axle. Each of the joints of the axle acts as a crank.
- Cam: This is basically a rotating object that pushes a follower as it moves. A cam transforms rotary motion into reciprocating motion in the follower or bar.
- Eccentric Cam: This consists of a wheel with an off-centre rotation axle that doesn’t coincide with the centre of its circumference.
Other Mechanisms
Mechanisms for Controlling and Directing Motion
The most typical mechanism of this type is the ratchet, which allows rotation in one direction but impedes it in the opposite direction, as you can see in the diagram.
- Disc Brakes: Consist of pads and a disc attached to the object that we want to slow down.
- Band Brakes: Consist of a metal band that puts pressure on a drum attached to the axle of the object we want to slow down.
- Drum Brakes: Include one or two brake shoes that come into contact with the drum.
Mechanisms That Store Energy
Springs are devices that absorb energy that can be released later, little by little or all at once.
Connecting Mechanisms
- Clutches: Are mechanisms that allow axles or shafts to be connected.
- Fixed Connections: Are used to make permanent connections between axles and shafts.
- Movable Connections: Are used to connect shafts that can move along the axle or at an angle to each other.