Fingerprints are unique to each person and can be classified into certain groups, according to geometric patterns of their lines and ridges. Fingerprints can be collected from a crime scene for instance, and saved for comparison with known prints.
The skin of the human hands (and feet) is covered with tiny ridges called friction ridges. The ridges enable people to easily pick up and handle objects. Much like running shoes, which have ridges on the bottom to prevent us from slipping, fingers and feet have natural ridges that serve the same purpose. Each person has a totally unique pattern of ridges on her skin. Even identical twins have different ridges!
A finger print is the image of these ridge patterns transferred to a surface. Historically, many people thought that fingerprints left on surfaces were a result of oily hands or hands that were soiled with dirt, paint or other substances. Actually, even scrubbed hands leave prints. Our hands (and feet) have an abundance of sweat glands, which secrete liquids that leave the patterned mark of our prints on almost everything we touch. These prints may be hard to see, and may need special treatment with chemicals or dust to become visible. Hard-to-see prints are called latent prints, as opposed to the visible prints left by soiled hands.
Many centuries ago, Chinese and Japanese emperors signed papers with thumbprints. It was not until the 1800s that fingerprints were used to link a suspect with a crime. In 1880, Dr. Henry Faulds, an Englishman working with the Japanese, published an article in the journal Nature detailing how he used fingerprints left on a fence to help free an innocent man charged with theft. It wasn’t long before Scotland Yard began to use fingerprinting as part of their investigations, and other agencies followed suit. As more police departments began to use prints, the need for classification and organization became clear.
In this activity, students too will discover a need to classify the prints they take. The prints on this page introduce you to the major categories of one commonly-used system of fingerprint identification. We suggest that you encourage children to develop their own classifications and nomenclature before looking at a standardized system.
1 hour a day, for 2 days
Ask each students to describe what makes other students unique. Students may list characteristics such as moods and manners. Note how many factors, taken individually, are common to several students. Is there any one physical characteristic that is totally unique to each person?
Some students may suggest fingerprints, since fingerprinting is commonly seen on television and discussed in mystery books. Ask the students to use magnifying glasses and look at their own index-finger ridges and those of a friend. Ask them to describe in words and then draw what they see. (You may hear words like “wiggle,” “swirley,” “twist,” and see drawings that look like wild mazes.)
Now demonstrate how to make different types of impressions. For ink impressions, press one finger at a time onto an inkpad. Don’t get it too wet. With help from friends, press and roll the finger on paper. For pencil impressions, scribble pencil on a paper until an area of the paper is darkened completely. Press your finger on this pencil residue. Stick a piece of clear tape on the pad of your finger and pinch down on the tape. Lift the tape, and—voila!—your fingerprint appears clearly on the tape.
Ask students to work in teams. Each student in a team should make an index-finger and a pinkie-finger print. Encourage teams to experiment with various methods of obtaining prints. Each set of prints should be put on an index card and labeled with the student’s name. Students should clearly label “index” or “pinkie” and note whether it was from their right or left hand. These cards will become each group’s fingerprint reference file.
While the groups are busy making prints for their files, take a second set of each child’s index and pinkie prints on your own cards. (Make sure you take prints from the same hand the child has printed.) Write a code on the cards that will help you identify the print, but will keep the prints’ owner a secret from the rest of the class.
Distribute to each group one of the prints that you took. You may wish to circle either the pinkie print or the index finger print. Ask if the students can find the owner of the print. You can greatly simplify this challenge by making sure the print you give each group belongs to someone in that group or by identifying a subset of the class to investigate; left-handers, students whose name begins with M, etc.
The students may feel daunted by their task as they line up print after print. Call the teams together after about ten minutes and ask if there is a way in which they can eliminate some prints. This may lead children into grouping prints by common patterns. They may wish to identify and label the most visible pattern in each of the prints on the index cards. From there they can look for the most distinguishing feature on the mystery card and find its match.
Fingerprinting - a Lesson on Classification
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