Simple Machines Study Guide for McGraw-Hill's Firefighter Exams
A machine is any device that applies mechanical energy at a given point and delivers it in a more efficient form at another point. There are many kinds of machines with varying capabilities and functions. Specifically, machines are used
- to transform energy from one type to another (steam turbine)
- to transfer energy (automobile drive train)
- to increase force (pry-bar)
- to multiply speed (bicycle gears)
- to change the direction of force (pulleys)
- to reduce friction (rollers)
Machines may be powered by motors, engines, or simply human effort. Prior to the age of motors and engines, animals were used to assist workers in moving and lifting heavy objects.
Simple machines were invented and used to overcome resistive forces and enable workers to get the job done. Firefighters have been using simple machines to perform the work they do since ancient times. Some of the simple machines they use daily include the axe, pry-bar, hook, hammer, pliers, vice-grip, shovel, crowbar, chisel, screwdriver, wheelbarrow, wedge, chock, pulley, block and tackle, hydraulic spreading and cutting tools, jacks, bulldozer, backhoe, and many, many more.
Simple machines are normally used when the amount of force required cannot be applied without the aid of a machine. They are also used to change the direction of effort (force) when the direction of the force to be applied is not the desired one, as in a pulley. An important point to understand is that most simple machines do not save energy; they simply allow the force required to do the work to be distributed over a longer distance or to be increased over a shorter distance. They provide a gain in effort (force) or a gain in distance, but not both. Common simple machines are the inclined plane, wedge, screw, lever, wheel and axle, pulley, and gear and belt drive.
More complicated (complex) machines are basically combinations of two or more simple machines. Machines that transform heat energy into mechanical energy are known as engines (steam engine and internal combustion engine). Electric motors change electrical energy into mechanical energy.
What Is Mechanical Advantage?
As stated above, simple machines are used to reduce the amount of force needed to perform a given task, such as moving heavy objects or lifting a load. By definition, a machine is a device that provides a mechanical advantage (MA). However, there is a trade off when simple machines are used: you must apply this force over a greater distance than if the load were moved directly. When trading off effort for distance, the advantage gained of increasing our effort force is called a mechanical advantage. The mechanical advantage of a machine is the factor by which a machine multiplies the force or effort being exerted on it. The mechanical advantage is a ratio of a load to the applied force (MA = load/applied force). A mechanical advantage greater than 1 is considered good. The greater the mechanical advantage, the less force or effort is required to accomplish the task.
How to Calculate Mechanical Advantage
Basic equations for finding the mechanical advantage of simple machines are:
Types of Simple Machines and Their Mechanical Advantage
Simple machines are derived from either the inclined plane or the lever. Seven common simple machines are:
- The inclined plane
- The wedge
- The screw
- The lever
- The wheel and axle
- The pulley
- The gear and belt drive system
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