9-3-simple-machines_summary

This section is about simple machines, which are devices that help perform work by reducing the force required or increasing the distance over which a force is applied, but do not change the amount of work being done. The section covers calculating mechanical advantage and efficiency of simple machines, such as levers, inclined planes, wedges, screws, and pulleys. Complex machines, which are combinations of two or more simple machines, are also discussed. Learning objectives for this section include describing simple and complex machines, calculating mechanical advantage and efficiency of simple machines, and defining input work, output work, and mechanical advantage. The High School Physics Laboratory Manual addresses content in this section in the lab titled "Work and Energy". Key terms in this section include effort force, resistance force, mechanical advantage, ideal mechanical advantage, fulcrum, effort arm, resistance arm, wheel and axle, and efficiency. Simple machines reduce the amount of force required to perform work, but the total amount of work remains the same. This is because of the conservation of energy, which states that the total amount of energy in a closed system remains constant. A simple machine can be useful because it allows for the reduction of force and the decrease in the distance over which force is applied, making work easier. Mechanical advantage is a number that tells us how many times a simple machine multiplies the effort force. The ideal mechanical advantage is the mechanical advantage of a perfect machine with no loss of useful work caused by friction. The equation for ideal mechanical advantage is: IMA = resistance force / effort force or IMA = distance over which effort is applied / distance the load moves For a simple machine, the work put into the machine is equal to the work the machine puts out. This means that if you know the work input and output, you can calculate the mechanical advantage. Efficiency of a machine is the ratio of the output work to the input work multiplied by 100 to express it as a percentage. Efficiency is always less than 100 percent in simple machines because of friction, which converts some of the work into heat energy. This section provides several examples of simple machines and their ideal mechanical advantages, such as levers, inclined planes, wedges, screws, and pulleys. The efficiency of these machines is also discussed. It is noted that complex machines, which are combinations of two or more simple machines, also have ideal mechanical advantages that can be calculated by multiplying the ideal mechanical advantages of their individual components. The section concludes with practice problems and check your understanding questions to help readers apply the concepts covered in the section.