Abstract

Objective

The purpose of this science project is to learn more about the field of forensic science by performing balloon spatter experiments.

Introduction

The word forensic comes from the Latin word forensis, which means of or before the forum. "During the time of the Romans, a criminal charge meant presenting the case before a group of public individuals in the forum. Both the person accused of the crime and the accuser would give speeches based on their side of the story. The individual with the best argument and delivery would determine the outcome of the case. Basically, the person with the sharpest forensic skills would win. This origin is the source of the two modern usages of the word "forensic"—as a form of legal evidence and as a category of public presentation" (Wikipedia, 2008). Today, the use of scientific evidence is so prevalent in the courtroom that the term forensics has become associated with forensic science. Forensic science is any science that is used in the courts or judicial system and it is extremely vital. The goal of a forensic scientist is to remain impartial and to appraise all of the available evidence in order to determine the truth.

Click here to watch a video of this forensics investigation, produced by DragonflyTV and presented by pbskidsgo.org.

Forensic science includes many areas of study, such as criminalistics, engineering science, and pathology and biology. If a sports player were to die suddenly while playing a game, a forensic scientist with a specialty in pathology and biology would be called in to find out the cause. The scientist may have to perform an autopsy and examine the body to determine if the death was natural or not. A forensic engineer applies engineering principles to the purposes of law investigations. For example, engineers study failure analysis and evaluate the quality of construction and manufacturing of structures involved in a crime or catastrophic event. They may look into why a particular car rolled over or why a building or bridge collapsed. In general, to become a forensic scientist, you need to study math and science.

This project is based on the Dragonfly episode "Forensics." In this episode, Kalia and Carolyn apply forensics to a birthday party crime scene. They collect evidence, come up with a list of possible suspects, and apply different methods to extract information from all of the evidence. Check out the video to see Kalia and Carolyn solve this mystery.

While Kalia and Carolyn solved a birthday party crime, this science fair project will be a little more gruesome. Investigate how blood spatters when a body hits something hard and fast. You will be figuring out how blood spatters as a function of height, except that you will be using water-filled balloons as models for bodies with real blood. Try your hand at collecting evidence and remember that solving mysteries is serious work!

Figure 1. This is a forensic scientist examining spatter. (Courtesy of the American Academy of Forensic Sciences Brochure and www.aafs.org, 2008.)

Terms, Concepts, and Questions to Start Background Research

• Forensic science
• Evidence
• Velocity
• Vector

Questions

• What is forensics?
• What are the different areas of study in forensic science?
• What kinds of projects do forensic scientists work on?

Bibliography

The following sources will help you learn more about forensic science:

• Wikipedia Contributors. (2008, May 16). Forensic science. Wikipedia: The Free Encyclopedia. Retrieved May 5, 2008 from http://en.wikipedia.org/w/index.php?title=Forensic_science&oldid=212886781
• TPT. (2006). Forensics by Kalia and Carolyn. DragonflyTV, Twin Cities Public Television. Retrieved May 5, 2008 from http://pbskids.org/dragonflytv/show/forensics.html
• Wikipedia Contributors. (2008). Bloodstain pattern analysis. Wikipedia: The Free Encyclopedia. Retrieved May 5, 2008 from http://en.wikipedia.org/w/index.php?title=Bloodstain_pattern_analysis&oldid=207162335
• Layton, Julia. (2008). How Crime Scene Investigation Works. Howstuffworks. Retrieved May 5, 2008 from http://science.howstuffworks.com/csi.htm

• American Academy of Forensic Sciences. (2008). Resources—Choosing a Career: So You Want to Be a Forensic Scientist! Retrieved May 16, 2008 from http://www.aafs.org/choosing-career

Materials and Equipment

• Water balloons, which are different from regular party balloons (10); available at party or novelty stores
• Digital kitchen scale
• Ladder (optional)
• Large clean concrete area
• Measuring tape
• Stopwatch
• Helper
• Lab notebook
• Graph paper

Experimental Procedure

1. Fill 10 water balloons with the same amount of water. Use a scale to confirm that the water balloons all weigh the same amount, plus or minus 10 percent. For example, if your first balloon weighs 5 ounces (oz) then the rest of the balloons should weigh between 4.5 and 5.5 oz.
2. Find a location that has a large, clean concrete area with steps that you can climb for different heights. Or you can use a ladder on a large clean concrete area. If you use a ladder, make sure that you have someone holding the ladder for safety.
3. Start by standing on the ground. Have your helper hand you a water-filled balloon. Hold the balloon straight out in front of you.
4. Now have your helper measure the distance of the balloon from the ground with the tape measure. Have your helper record this data in your lab notebook, using a data table similar to the one below.
5. Have your helper use the stopwatch to time how long it takes for the balloon to fall and spatter. Release the balloon and observe the spatter that it makes on the concrete. Note the time in your lab notebook. If the balloon doesn't break at this distance go to step 7 and increase your starting distance.
   1. Calculate the speed, or velocity, of the balloon. Write the value down in your lab notebook. Velocity is described in Equation 1.

      Equation 1:

      Velocity (feet/second or meters/second)	=	(Distance the balloon is from the ground/Falling time) in a direction
      V	=	∆X   ∆t	in a direction

      V = velocity. Velocity is a vector quantity, which means that it has a direction associated with it. ∆X = Change in height or the distance from the ground ∆t = Falling time

   2. Measure the size of the initial impact. Is it a circular shape or an oblong shape? Is the impact longer in one direction than in another? Note this data in your lab notebook.
   3. Measure the length from the center of the initial impact to the outermost spatter or drop of water. Note this data in your lab notebook.

      Figure 2. This is a diagram of spatter.

6. Repeat step 5 two more times. Note the data in your lab notebook.
7. Increase your distance from the ground and then repeat steps 5 and 6. Increase the distance at least two times beyond the starting distance. There should be three trials for each distance. Record all data in your lab notebook. Each time that you step up a stair, have your helper measure the height of that one stair. Add the height of the stair to the previous distance of the balloon from the ground to calculate the new distance of the balloon from the ground.
8. Plot the data that you collected.
   1. Plot the distance from the ground (x-axis) versus the size of the initial impact (y-axis).
   2. Plot the distance from the ground (x-axis) versus the length from the center of the initial impact to the outermost spatter (y-axis).
   You can also redo these plots to have velocity on the x-axis.

   Distance of Balloon from Ground	Trial	Falling Time	Velocity	Spatter Observations
   Distance 1=	1			Initial impact size=	Distance between initial impact and outermost spatter=
   	2			Initial impact size=	Distance between initial impact and outermost spatter=
   	3			Initial impact size=	Distance between initial impact and outermost spatter=
   Distance 2=	1			Initial impact size=	Distance between initial impact and outermost spatter=
   	2			Initial impact size=	Distance between initial impact and outermost spatter=
   	3			Initial impact size=	Distance between initial impact and outermost spatter=

Variations

• Instead of dropping the water balloon straight down, try throwing the water balloon at angles to the ground. How does this change the size and shape of the initial impact and where the spatters end up?
• Repeat the science project over a surface other than concrete.
• This original science project kept the balloons at a near constant weight and varied the height. What happens when you keep the height constant and vary the weight of the balloons?

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies

Special thanks to Mr. Geoff Bruton, of the Ventura County Sheriff's Department Forensic Sciences Laboratory Firearms & Toolmarks Section, for valuable discussion.

This project is based on a Dragonfly TV project: TPT. (2006). Forensics by Kalia and Carolyn. DragonflyTV, Twin Cities Public Television. Retrieved May 5, 2008 from http://pbskids.org/dragonflytv/show/forensics.html

Last edit date: 2011-05-04 22:00:00