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Simple machines

Engineering is the use of physics to design something – such as machines, electrical devices, buildings, vehicles, and infrastructure. In this lesson we start by looking at the most basic elements of engineering, the simple machines.

A simple machine is a mechanical device that changes the direction or magnitude of a force.

They are the simplest mechanisms that use mechanical advantage to multiply force.

The term usually refers to the six classical simple machines defined by Renaissance scientists:

1. Lever

first order lever

second order lever

2. Wheel and axle

A wheel can be attached to a long thin rod; the wheel has a larger diameter than the rod.

The wheel rotates when a force is transferred from the axle to the wheel.

wheelandaxle

On any practical device, a hinge or bearing must support the axle, allowing rotation.

Cranked axle

cranked-axle

.

3. Pulley

A pulley is a wheel on an axle or shaft.

It is designed to support movement and change of direction of a taut cable or belt,

or it can transfer power between the shaft and cable or belt.

pulley simple machine

4. Inclined plane

An inclined plane, also known as a ramp.

A flat supporting surface tilted at an angle used as an aid for raising or lowering a load.

Moving an object up an inclined plane requires less force than lifting it straight up.

The cost is that there is an increase in the distance moved.

mechanical-advantageofinclinedplane

5. Wedge

A wedge is a triangular shaped tool, or a portable inclined plane. It can separate two objects, or portions of an object,  It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces.

6. Screw

A screw converts rotational motion to linear motion.

It converts torque (rotational force) to a linear force.

The most common form consists of a cylindrical shaft with helical grooves (“threads”) around the outside.

The screw passes through a hole in another object, with threads on the inside of the hole that mesh with the screw’s threads.

screw animation by Tapolako

screw animation by Tapolako

A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force.

The machine can increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load. The ratio of the output to the applied force is called the mechanical advantage.

Simple machines are the building blocks of which more complicated machines (“compound machines”) are composed.

Other simple machines

Gears (or cogwheel)

A rotating machine part having cut teeth, or in the case of a cogwheel, inserted teeth (called cogs), which mesh with another toothed part to transmit torque.

Geared devices can change the speed, torque, and direction of a power source.

Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio. Thus they may be considered a simple machine.

The teeth on the two meshing gears all have the same shape. Two or more meshing gears, working in a sequence, are called a gear train or a transmission.

A gear can mesh with a linear toothed part, called a rack, producing translation instead of rotation.

Inter meshing gears rotational motion

Animation from OSHA Directorate of Technical Support and Emergency Management , Machine guarding

“Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster. Since the larger gear is rotating less quickly, its torque is proportionally greater. One subtlety of this particular arrangement is that the linear speed at the pitch diameter is the same on both gears” – Wikipedia, gears

Lesson on gears from dynamicscience.com.au

 

History of simple machines

(This section has been adapted from the Wikipedia article, ‘Simple Machine’ (2/5/2019)

The idea of a simple machine originated with the Greek philosopher Archimedes around the 3rd century BCE. In particular he analyzed the use of the lever, pulley, and screw, discovering the principle of mechanical advantage in the lever. Archimedes’ famous remark with regard to the lever: “Give me a place to stand on, and I will move the Earth.” (Greek: δῶς μοι πᾶ στῶ καὶ τὰν γᾶν κινάσω) expresses his realization that there was no limit to the amount of force amplification that could be achieved by using mechanical advantage.

Later Greek philosophers defined the classic five simple machines (excluding the inclined plane) and were able to roughly calculate their mechanical advantage. Note that the Greeks’ understanding was limited to the statics of simple machines (the balance of forces), and did not include dynamics, the tradeoff between force and distance, or the concept of work.

During the Renaissance the dynamics of simple machines were studied from the standpoint of how far they could lift a load, in addition to the force they could apply. This led to the new concept of mechanical work. In 1586 Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, and it was included with the other simple machines. A complete dynamic theory of simple machines was worked out by Italian scientist Galileo Galilei in 1600 in Le Meccaniche (On Mechanics), in which he showed the underlying mathematical similarity of the machines as force amplifiers. He was the first to explain that simple machines do not create energy, they only transform it.

The great variety of modern machine linkages, which arose during the Industrial Revolution, is inadequately described by these six simple categories. As such, post-Renaissance authors have compiled expanded lists of “simple machines”, often using terms like basic or compound machines, to distinguish them from the classical simple machines above. By the late 1800s, Franz Reuleaux had identified hundreds of machine elements, calling them simple machines. Modern machine theory analyzes machines as kinematic chains composed of elementary linkages called kinematic pairs.

Apps

COSI Simple machines

Resources from CPO Science

Ropes & pulleys Powerpoint

Levers Powerpoint

Gears Powerpoint

Labs forms and instructions for gears and levers: PDF file

Learning Standards

Massachusetts Science and Technology/Engineering Curriculum Framework

Appendix VIII Value of Crosscutting Concepts and Nature of Science in Curricula

Cause and Effect: Mechanism and Explanation. Events have causes, sometimes simple, sometimes multifaceted. A major activity of science and engineering is investigating and explaining causal relationships and the mechanisms by which they are mediated. Such mechanisms can then be tested across given contexts and used to predict and explain events in new contexts or design solutions.

Technology/Engineering

HS-ETS3-3(MA). Explain the importance of considering both live loads and dead loads when constructing structures. Calculate the resultant force(s) for a combination of live loads and dead loads for various situations.

  • Examples of structures can include buildings, decks, and bridges.
  • Examples of loads and forces include live load, dead load, total load, tension, sheer, compression, and torsion.

HS-ETS3-4(MA). Use a model to illustrate how the forces of tension, compression, torsion, and shear affect the performance of a structure. Analyze situations that involve these forces and justify the selection of materials for the given situation based on their properties.

  • Examples of structures include bridges, houses, and skyscrapers.
  • Examples of material properties can include elasticity, plasticity, thermal conductivity, density, and resistance to force

HS-ETS4-5(MA). Explain how a machine converts energy, through mechanical means, to do work. Collect and analyze data to determine the efficiency of simple and complex machines.

7.MS-ETS3-4(MA). Show how the components of a structural system work together to serve a structural function. Provide examples of physical structures and relate their design to their intended use.

Clarification Statements:

  • Examples of components of a structural system could include foundation, decking, wall, and roofing.
  • Explanations of function should include identification of live vs. dead loads and forces of tension, torsion, compression, and shear.
  • Examples of uses include carrying loads and forces across a span (such as a bridge), providing livable space (such as a house or office building), and providing specific environmental conditions (such as a greenhouse or cold storage).

College Board Standards for College Success: Science

Standard PS.1 Interactions, Forces and Motion

Changes in the natural and designed world are caused by interactions. Interactions of an object with other objects can be described by forces that can cause a change in motion of one or both interacting objects. Students understand that the term “interaction” is used to describe causality in science: Two objects interact when they act on or influence each other to cause some effect. Students understand that observable objects, changes and events occur in consistent patterns that are comprehensible through careful, systematic investigations.

Benchmarks, American Association for the Advancement of Science

In the 1700s, most manufacturing was still done in homes or small shops, using small, handmade machines that were powered by muscle, wind, or moving water. 10J/E1** (BSL)

In the 1800s, new machinery and steam engines to drive them made it possible to manufacture goods in factories, using fuels as a source of energy. In the factory system, workers, materials, and energy could be brought together efficiently. 10J/M1*

The invention of the steam engine was at the center of the Industrial Revolution. It converted the chemical energy stored in wood and coal into motion energy. The steam engine was widely used to solve the urgent problem of pumping water out of coal mines. As improved by James Watt, Scottish inventor and mechanical engineer, it was soon used to move coal; drive manufacturing machinery; and power locomotives, ships, and even the first automobiles. 10J/M2*

The Industrial Revolution developed in Great Britain because that country made practical use of science, had access by sea to world resources and markets, and had people who were willing to work in factories. 10J/H1*

The Industrial Revolution increased the productivity of each worker, but it also increased child labor and unhealthy working conditions, and it gradually destroyed the craft tradition. The economic imbalances of the Industrial Revolution led to a growing conflict between factory owners and workers and contributed to the main political ideologies of the 20th century. 10J/H2

Today, changes in technology continue to affect patterns of work and bring with them economic and social consequences. 10J/H3*

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