How machines help us

Introduces basic principles of the lever, wheel and axle, pulley, inclined plane, wedge, and screw, and shows common usage of each. Shows the crowbar as a lever, and shows a doorknob as an example of a wheel and axle. Pictures the raising of the flag to illustrate the use of a pulley. Shows stairs as an example of an inclined plane, pictures carpenters driving nails as wedges, and presents the operation of an auto jack as an example of a screw.