Blood Spatter Analysis

Health Sciences
Health Sciences
Created by
University of Ottawa and Carleton University
Activity Language
English
Grade
Grades 11-12
Time Needed for Activity
1-2 hours
Subjects
Health Science,  Physics
Good for Virtual Delivery

In this activity, students will use blood spatter and physics principles to solve a crime.

What You Need

Materials per pair of students

  • Cup for water
  • Foam paintbrushes (2 per group)
  • 2 ounces of red paint (in a conical tube)
  • Large piece of paper (from a roll)
  • 8 oz paper cup
  • Sheet of clear plastic or tarp
  • String (1 metre)
  • Scotch tape
  • Magnifying glass
  • Blood spatter posters

Guide:

Presentation:

Additional:

Blood Spatter Posters:

Safety Notes

Ensure you are familiar with Let's Talk Science's precautions with respect to safe virtual outreach to youth.

Students should be careful with fake blood, it could become slippery if it spills. Paintbrushes and fake blood should not be thrown while making the spatter. 

What To Do

Introduction

  • Using the presentation, go over the 5 myths to Hollywood CSI, including:
    • One or two people can solve a crime.
    • CSI are the main players.
    • Science in shows are always realistic.
    • DNA or fingerprints can solve every case.
    • Blood spatter is evidence.
  • Explain the difference between the terms "splatter" and "spatter".
  • Discuss the 4 main components of blood:
    • Plasma
    • Red blood cells
    • White blood cells
    • Platelets
  • Discuss how the height or angle of a drop will affect blood spatter.
  • Go over the information that will help them with their activity.

Activity: Make your own Spatter

  • Have students tape the plastic liner along the floor and wall for the blood spatter activity. They will place their roll of paper along the plastic and then spatter paint on it, so the plastic needs to cover the area where the paint might go outside of the paper. 
  • Distribute brushes, cups and paint.
  • Instruct them to dip a paintbrush in the fake blood/paint and make their own spatter patterns on the paper.
  • Instruct them to try different heights, force and angle for their spatter. You could put up Slide 9 of the presentation to show the patterns.
  • After 10 minutes, have students clean up the paint and brushes.
  • Discuss their observations - how did height and angle affect the blood spatter?

Activity: Mini-Crime Scene Investigation 

  • Explain the scenario: They are a crime scene investigator and it is their job to find the point of origin from a blood spatter. The case story is supplemental and may help them find clues to determine what happened, but the main mission is to find the angle of impact.
  • Distribute the case study sheets, string and tape.
  • Students will use the bullet points on the sheets to find the point of origin from the spatter shapes using strings and tape.
  • Have students race to solve the crime.

Wrap-up

  • Have one or more groups present their crime scene analysis.
  • Let them know that one of the crimes was not solvable with the info they had, is this a realistic scenario?
  • Discuss possible careers related to the topics discussed in today's workshop and what they will need (education, experience, etc.) to get into those careers.

Discovery

How does height and angle affect how a drop will spatter?

Because of ion cohesion two things can happen:

  • The higher the spatter falls from, the larger the droplet will spread out when it hits the surface. Because of ion cohesion it will still form a droplet. The tiny spots that bounce off from the droplet are called satellite spots.
  • If spatter drops fall from the same location over and over again, the ions may remain cohesive and form a bigger droplet (depending on the force the spatter is falling with).

The shape of blood spatter can be used to determine where the spatter came from (point of origin). When the force of a motion is hard enough to distort the droplet (overwhelm the ionic cohesion) or comes from an angle, the spatter shape can change from a regular droplet. The portion of the spatter that elongates is called the tail, the 'round' portion of the drop is called the head. The tail will point away from the direction of the spatter came from.

Golden rule: the smaller or more narrow the angle of impact, the more elongated the drops will be with longer tails.

DNA analysis cannot be used to solve every case, scientists also use databases and other means (such as blood spatter analysis) to figure out what occurred. Crime scene investigation involves a large team of professionals working together to solve the crime, such as first responders, detectives, crime scene investigators and reconstructionalists, laboratory scientists and coroners/medical examiners.

  • As a further challenge, students may use the information provided from the case studies to try to determined how the crime really occurred.

What's Happening?

How does height and angle affect how a drop will spatter?

Because of ion cohesion two things can happen:

  • The higher the spatter falls from, the larger the droplet will spread out when it hits the surface. Because of ion cohesion it will still form a droplet. The tiny spots that bounce off from the droplet are called satellite spots.
  • If spatter drops fall from the same location over and over again, the ions may remain cohesive and form a bigger droplet (depending on the force the spatter is falling with).

The shape of blood spatter can be used to determine where the spatter came from (point of origin). When the force of a motion is hard enough to distort the droplet (overwhelm the ionic cohesion) or comes from an angle, the spatter shape can change from a regular droplet. The portion of the spatter that elongates is called the tail, the 'round' portion of the drop is called the head. The tail will point away from the direction of the spatter came from.

Golden rule: the smaller or more narrow the angle of impact, the more elongated the drops will be with longer tails.

Why Does It Matter?

DNA analysis cannot be used to solve every case, scientists also use databases and other means (such as blood spatter analysis) to figure out what occurred. Crime scene investigation involves a large team of professionals working together to solve the crime, such as first responders, detectives, crime scene investigators and reconstructionalists, laboratory scientists and coroners/medical examiners.

Investigate Further

  • As a further challenge, students may use the information provided from the case studies to try to determined how the crime really occurred.

Resources