What are they?
Prostheses are "false body parts" used to replace parts that have been amputated or never properly developed. They are manufactured from different materials, primarily man made alloys.
Why are they used?
Any person who has had to do without a particular body part for any length of time understands how difficult managing everyday life can be. A prosthetic device will assist the person in coping with regular activities. Currently many athletes who have lost legs or arms wear specialty prosthetics which allow them to continue in their competition!
The History Behind Prosthetics.
The first types of prostheses originated at the "dawn of time" and were carved from wood, or any other natural material. The Romans are known for their adoption of this technique and the advances they made. More recently, prostheses are made to move just as a regular limb in order for normal activity to be resumed. WWII led to a larger population of amputees which caused more attention to be devoted to the production of prosthetics.
The Physics Behind the Devices.
Prosthetic devices must be designed to: fit the person, withstand the force of that person's weight, withstand the person's motion, be durable for the person's activity level, and be suitable for the person's environment.