238
Technology: Engineering Our World
The Wheel and Axle
The wheel and axle is a simple machine that consists of a large diameter
disk or wheel that is attached rigidly to a smaller diameter bar (axle).
Effort applied to the outer edge of the wheel is transmitted through the
axle. Think of it as a special kind of Class 1 lever. See Figure 8-24.
Like levers, the wheel and axle contains three elements: effort, fulcrum,
and resistance. In the case of the doorknob, the effort is applied to the
rim of the wheel (knob). The knob multiplies the effort and transmits it
through the axle (bar). The resistance is the door latch.
Even the simple pizza cutter uses a wheel and axle. The effort is
supplied by the person pressing on the handle and the resistance is the
force of the wheel on the pizza. See Figure 8-25.
The Inclined Plane
There are at least two ways of loading the furniture onto the truck
in Figure 8-26. One way is simply to lift it. However, it is much easier
and safer to push the motorcycle up a sloping plank. The sloping surface
formed by the plank is called an inclined plane or ramp.
Change motion
through 90°
Transmit motion Change speed Reverse direction
of motion
Flexible
belt
gure 8-23. Pulleys can transmit motion from one point to another.
A B
gure 8-24. A—A doorknob is a common example of the wheel and axle. B—Where are the
effort, fulcrum, and resistance?