Does the Height of a Blood Drop Affect How It Lands on a Surface?

Introduction

Criminals always leave behind traces of evidence. It is the work of forensic scientists to go back to the crime scene, collect any traces left behind, and try to make sense of it. Blood spatter analysis is one of the most common ways these investigators try to collect evidence that could help in a criminal investigation. Blood spatter analysis is an experiment where scientists study the characteristics of bloodstain to determine the events that could help explain its origin. This analysis answers the question of whether the height from which a drop of blood drops affects the way it lands on the surface. Forensic scientists utilize this experiment to determine the shape, size, distribution, and location of the bloodstain. However, in this case, we use the experiment to determine the diameter of the bloodstain after dropping from different heights. Instead of using human blood, the experiment uses simulated blood, which could give inaccurate results as compared to human blood. However, given the dangers associated with collecting human blood samples, the simulated blood was necessary. The results of the experiment may confirm or refute the hypothesis that the higher the blood drop falls from, the larger the diameter it covers on the surface it strikes.

Body of Research

Background

The origin of investigating the characteristics of bloodstain spatter dates back a century after a historian working with the International Association of Bloodstain Spatter Analysis (IABPA) found literature on it from an article published by Eduard Piotrowski on experiments on blood characteristics from a head wound. Piotrowski conducted experiments by observing and documenting what happened to their blood after beating them to death. One of his findings that is still being used in violent criminal investigations to date was that bloodstains started appearing after the second blow. However, before criminal investigators use this assumption, they have to make sure that the bloodstain is a result of a blow. Several other publications after that of Piotrowski followed and shed more light on the investigation of bloodstains in solving crimes. It is from his work that the IABPA was founded, and from that, it has continued to support the continuing development of this experiment.

Problem Statement

Despite the continued support in advancing the field of forensic science in crime scenes, there is still confusion about what these specialists look for during an investigation. A comprehensive understanding of the different characteristics of blood at a crime scene could help solve many cases by helping to recreate the sequence of events that could help solve a violent crime. While there has been wide research in the area, there still lacks a systematic explanation, especially to the general public, of the characteristics to look for when interpreting blood spatter patterns. This research aims to address this issue by investigating how the height of a blood drop affects how it lands on a surface. Understanding the influence of height could help forensic scientists enhance the reliability of their blood spatter analysis and improve the accuracy of forensic methodologies while contributing to the growth and precision of criminal investigation.

Hypothesis

The higher the blood drop falls from, the larger the diameter of the cover on the surface it strikes.

Materials and Procedure

In order to find the relationship between the height of the drop and the diameter of the spatter, it is important to create a scenario that can be related to a real crime scene. While real implications can only be established with real human blood, given the unique qualities of blood at a crime scene, using it could have limitations to the experiment. Similarly, since the experiment does not aim to cause any harm that could result from collecting real human blood samples, simulated blood made from cornstarch, corn syrup, and red food coloring will be used. The simulated blood imitates the many physical properties of blood, including viscosity, density, and surface tension, making it suitable for the experiment as they could be contrived in ways to replicate the properties of real human blood.

After making the simulated blood, fill a medicine dropper and manually drop three drops from five different heights, starting from 30cm and increasing the heights by 30cm until 150cm. The simulated blood is steadily squeezed from the dropper at a constant volume, falling on a 30cm by 30 cm cardboard. Each time the same volume was dropped, the spatter was left to dry, and their diameter was recorded.

Analysis of Results

Results

Variables

Data Representation

Discussion

The results shown in the table and line graph above show that the height from which the simulated blood is dropped will be directly proportional to the resulting diameter of the bloodstain spatter. As the height increases, terminal velocity will drastically affect the size and diameter of the stain, causing the graph to appear linear. This is because velocity increases due to drag. It is, however, important to note that it is not always guaranteed that the bloodstains at a crime scene are downward directed.

Although this project deals with simulated blood, there are thousands of crime scenes that have real human blood where this experiment could be applicable and helpful in collecting evidence. It is what forensic experts deal with when conducting investigations involving violent crimes. Although criminal investigations are often accused of being subjective, this experiment is one of the best ways of beating such allegations since it works by obeying certain laws of physics that offer objective insight into cases. Successful interpretation of the diameter of the bloodstains could point investigators to useful cues on the nature of the crime, the sequence of events, and if there was any interference at the crime scene.

Conclusion

By means of the blood splatter experiment, we can affirm our hypothesis that the height of blood drop is directly proportional to the diameter of bloodstain once it strikes a surface. This experiment can be useful in the field of forensic science by helping experts collect evidence and gain insight into the sequence and nature of the crime.

Work Cited

Forensic Science Simplified. “Bloodstain Pattern Analysis: Principles.” Www.forensicsciencesimplified.org, 2013, www.forensicsciencesimplified.org/blood/principles.html.

Freeman, Shanna, and Melanie Radzicki McManus. “How Bloodstain Pattern Analysis Works.” HowStuffWorks, 24 Apr. 2008, science.howstuffworks.com/bloodstain-pattern-analysis1.htm.

Ly, Michael. “Kinematics and Blood Spatter Analysis.” Medium, Medium, 7 Nov. 2017, medium.com/@12378706/kinematics-and-blood-spatter-analysis-1a3fd733edb9.

Perkowitz, Sidney. “The Physics of Blood Spatter – Physics World.” Physics World, 17 Oct. 2019, physicsworld.com/a/the-physics-of-blood-spatter/.

Science Buddies. “Forensics: How Does It Matter? Measure the Spatter! | Science Project.” Science Buddies, 2023, www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p066/physics/forensics-measure-blood-spatter.

The Forensics Library. “Bloodstain Pattern Analysis – the Forensics Library.” Aboutforensics.co.uk, 2011, aboutforensics.co.uk/bloodstain-pattern-analysis/.