Question

unit 3: forensic laboratory techniques

1. what is the difference between sliding and spreading calipers? when would you use each?
2. based on the image to the right, what is the diameter of this bullet casing?
3. read the following experimental scenario:

your lab has been using cyanoacrylate vapor, aka superglue fuming, to process latent fingerprints, but you are not sure the procedure is producing the best prints possible. you decide to test three different variables: amount of time in the fuming chamber, brand of superglue, and method for heating the cyanoacrylate. your variables have been summarized in the table below.

variable	variations to test
brand of super glue	infinity bond, gorilla, loctite, scotch
method of heating	candle, hot plate, light bulb

using the same right forefinger, you place one print in the center of a glass slide, and then develop the print in the same fuming hood using a different combination of variables each time. for example, you use infinity bond super glue and a candle as the heating method, but then you vary the amount of time you run the test (5, 10, 15, 20, 25, and 30 minutes).
after each test, you determine whether the combination of variables was effective using two pieces of data: whether the ridge pattern is visible, and how many minutiae are visible in the final print.
answer the following questions based on the experimental scenario.
a) what is/are the independent variable(s)?
b) what is/are the dependent variable(s)?
c) what is/are the constant(s) in this experiment?
d) why is it important that you are only changing one variable at a time in this experiment? in other words, why did you change the amount of time but not the super glue brand or heating method?

Explanation:

1. Sliding calipers have one fixed and one sliding jaw for measuring internal/external dimensions directly. Spreading calipers have two movable legs and are used to transfer measurements or compare sizes. You'd use sliding calipers for precise measurements of an object's dimensions, and spreading calipers for tasks like marking out equal distances or transferring a measurement from one object to another.
2. Since no image details for the bullet - casing diameter measurement via calipers are given, we cannot answer this question precisely.

3.
a) Independent variables are the ones the experimenter manipulates. Here, they are amount of time in the fuming chamber, brand of super glue, and method of heating.
b) Dependent variables are the ones that are measured as a result of changes in independent variables. Here, they are whether the ridge pattern is visible and how many minutiae are visible in the final print.
c) Constants are the factors that remain the same throughout the experiment. Here, they are the right forefinger used for the print, the glass slide, and the fuming hood.
d) Changing only one variable at a time allows for clear identification of the impact of that specific variable on the dependent variable. If multiple variables are changed simultaneously, it becomes impossible to determine which variable caused the observed change in the dependent variable.

Answer:

1. Sliding calipers: One fixed and one sliding jaw for direct dimension measurement. Use for precise dimension measurements. Spreading calipers: Two movable legs for transferring or comparing measurements. Use for marking equal distances or transferring measurements.
2. No answer due to lack of image details.

3.
a) Amount of time in the fuming chamber, brand of super glue, method of heating.
b) Whether the ridge pattern is visible, how many minutiae are visible in the final print.
c) Right forefinger, glass slide, fuming hood.
d) To clearly identify the impact of a specific variable on the dependent variable. If multiple variables are changed simultaneously, it's impossible to determine which variable caused the change in the dependent variable.