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Mechanical Advantage

Introduction to the ratio of the output force to the input force of a machine.

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Freedom Chair

Freedom Chair

Credit: Mario Bollini
Source: http://www.flickr.com/photos/mesaba/4791522028/
License: CC BY-NC 3.0

A regular wheelchair would be useless over the rough terrain pictured above. But the wheelchair in the picture is no regular wheelchair. Called the “leveraged freedom chair,” it was designed for use in developing countries, where the terrain may be too rough for a regular wheelchair to navigate.

Why It Matters

  • At least 40 million people in developing nations need wheelchairs to move around but don’t have them. Wheelchairs are too expensive to buy and maintain. They also aren’t well suited for unpaved roads, mud, and other conditions typical in rural areas of the developing world. That’s where the leveraged freedom chair comes in.
  • Look at the picture above. Do you notice anything unusual about the wheelchair? The name of the wheelchair is a clue. It is leveraged, or operated by levers (the white-capped blue rods in the picture). Regular wheelchairs are operated by turning the wheels directly with the hands.
  • Credit: hdptcar
    Source: http://www.flickr.com/photos/hdptcar/2530801894/
    License: CC BY-NC 3.0

    Here is another off-road wheel chair operated using bicycle-like chains [Figure2]

  • What’s the advantage of a lever-operated wheelchair? The main advantage is mechanical—mechanical advantage, that is.
  • To learn more, watch this video about how and why the wheelchair was developed: http://www.ted.com/talks/amos_winter_the_cheap_all_terrain_wheelchair.html

What Do You Think?

Explore the Web site at the link below for more background on the leveraged freedom chair and its development. Be sure to check out the pictures and watch the videos. Then answer the following questions.

  1. What constraints guided the design of the leveraged freedom wheelchair?
  2. How do riders operate the freedom wheelchair? How do they operate a regular wheelchair?
  3. How do riders “shift gears” on the freedom wheelchair? Why does this make the wheelchair mechanically simple?
  4. Compare the mechanical advantage of the freedom chair with that of a regular wheelchair.
  5. How did developing country wheelchair users contribute to the design of the freedom chair?
  6. What do you think? How does the leveraged freedom wheelchair contribute to society in the developing world?

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Image Attributions

  1. [1]^ Credit: Mario Bollini; Source: http://www.flickr.com/photos/mesaba/4791522028/; License: CC BY-NC 3.0
  2. [2]^ Credit: hdptcar; Source: http://www.flickr.com/photos/hdptcar/2530801894/; License: CC BY-NC 3.0

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