Just Plane Simple Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Summary Introduction to the 6 simple machines.

Learning Objectives After this lesson, students should be able to: Explain how the inclined plane, wedge and screw make work easier. Identify how the inclined plane, wedge and screw are used in many familiar engineering systems today. Discuss the mechanical advantage of an inclined plane, wedge and screw.

Introduction Which of you students truly enjoy lifting or moving heavy objects?

Pre-Lesson Assessment Who does more work?: engineer Ed lifts a 200 lb. weight up to a height of 2 ft. and engineer Emma lifts a 50 lb. weight to a height of 8 ft. (Answer: They both do the same amount of work, 400 ft-lbs or 542 Joules of work. Use W = Fd.)

From the previous scenario, who did the work easier? (Answer: Engineer Emma, who used a force of only 50 lbs while engineer Ed used a force of 200 lbs.)

The most important fact is that simple machines never change the amount of work done

Work = Force x Distance

Inclined Plane Effort is distributed over a long distance. Steeper the slope the harder the effort.

Wedge Used for splitting or separating objects. Can you imagine how hard it would be to cut down a tree or chop wood without an axe?

Can you think of other devices where the wedge is at work? hull of a ship, airplane wings, and even our front teeth

Screw Turns rotational force into linear force. What are examples of screws? Propeller, a spiral staircase, nut and bolt, woodscrew, auger, drill bit, worm gear, and windmill

Lesson Background Mechanical Advantage makes work easier.

Mechanical Advantage (Incline Plane)

Mechanical Advantage (Wedge)

Wedge

Mechanical Advantage (Screw)

MA (Screw) Smaller pitch means greater mechanical advantage. Larger diameter means larger mechanical advantage.

Lesson Closure Since work is defined to be simply the product of force and distance, most tasks can be accomplished in many different ways, even though the amount of work done remains the same. Simple machines help us make work easier by applying a force over a greater distance. This fundamental idea enables the inclined plane to lift heavy objects with little effort, the wedge to easily cut rigid objects in two, and the screw to multiply a rotational torque into a linear force.

Engineers integrate these three machines in many useful devices today, such as stairs, highways, scissors, plows and airplanes. The mechanical advantage of a machine describes how the machine makes work easier. If the mechanical advantage of a machine is less than one, work is harder; however if the mechanical advantage is greater than one, work is easier.

True or False: The inclined plane has more mechanical advantage than both the wedge and screw. (Answer: False. While every simple machine provides mechanical advantage, each machine does not have a specific mechanical advantage associated with it.

True or False: The wedge and screw can be thought of as slight variations of the inclined plane. (Answer: True. The wedge is composed of two inclined planes set back to back and the screw is composed of wrapping an incline around a cylinder.)