Blood Spatter Patterns

Students design and conduct an experiment using fake blood to investigate how drop height affects the diameter and features of a bloodstain. By testing multiple heights (including those that approach terminal velocity), students observe trends in stain size and spatter patterns.

1. Gather materials: chart paper, fake blood, disposable pipette, metric ruler, yardstick or meter stick, markers, and optional step stool/ladder with supervision.
2. Tape chart paper to a flat, horizontal surface and label trial areas with intended drop heights (for example: 0.5 ft, 1 ft, 3 ft, 5 ft, 7 ft, 9 ft).
3. Practice releasing a single drop from the pipette without adding sideways motion; keep the tip aligned directly above the target.
4. Measure and mark the release height from the paper using the yardstick/meter stick; keep the pipette tip at this height for every trial at that level.
5. Release one drop onto the target area; allow the stain to stop spreading before measuring.
6. Measure the diameter of the circular portion of the stain (ignore satellites for the primary diameter) and record the value on the chart paper and in a data table.
7. Repeat at least 3 trials per height to improve reliability, refilling the pipette to a consistent volume each time.
8. Increase heights as safely permitted; if testing above table height, use a step stool or supervised ladder and ensure the paper surface and release point remain aligned vertically.
9. Optionally test different volumes (small vs. full pipette) to see how volume influences stain size; record volumes used.
10. After all trials, calculate mean diameter for each height and plot diameter (y) versus height (x); identify any plateau that suggests terminal velocity conditions.
11. Inspect patterns for satellites, scalloped edges, or elongation; note how surface type and repeated drops in the same spot can alter the pattern.
12. Clean the area following lab safety procedures.

Blood Spatter: How to Make Spatter - Heidi Hisrich:

📄 Blood Spatter Inquiry Lab - The Trendy Science Teacher: https://thetrendyscienceteacher.com/2023/01/13/blood-spatter-inquiry-lab-3/

📄 Forensics: How Does It Matter? Measure the Spatter! - Science Buddies: https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p066/physics/forensics-measure-blood-spatter

• Test different surfaces (copy paper, cardboard, tile, fabric) to compare how surface texture affects spreading and satellites.
• Keep height constant and vary drop volume to model the effect of volume on stain diameter.
• Keep height and volume constant but change the surface angle (0° vs. a gentle incline) to observe elongation and directional tails.
• Compare different fake blood formulations (with and without thickener) to explore viscosity effects.
• Use image analysis software or graph paper overlays to measure diameters more precisely and to quantify satellite counts.

• Use only fake blood; never use real blood.
• Wear safety glasses and gloves to prevent contact and stains.
• Do not ingest materials; keep food and drink out of the lab area.
• Secure chart paper with tape to prevent slipping hazards from spills.
• If standing on lab stations, verify they are sturdy, dry, and uncluttered; step up and down carefully and only with teacher permission.
• Use a step stool or ladder only with adult supervision; maintain three points of contact and keep the yardstick/meter stick clear of others.
• Wipe spills immediately with appropriate cleaner; dispose of paper and gloves according to classroom guidelines.
• Wash hands after the activity.

• How did stain diameter change as height increased, and did it level off at higher heights? (Diameter typically increases with height until it approaches a maximum when the drop reaches near-terminal velocity.)
• Why might two groups get different diameters at the same height? (Differences in drop volume, release technique, pipette squeeze force, or surface texture can change results.)
• What features indicate higher-energy impacts besides larger diameter? (More pronounced scalloped edges and increased satellite spatter are typical at higher impact energy.)
• How would a rough or absorbent surface affect the stain compared to a smooth, nonabsorbent surface? (Rough/absorbent surfaces usually reduce spreading and can suppress satellites, producing smaller, less defined edges.)
• If the drop is released with sideways motion, what happens to the shape? (The stain elongates in the direction of travel and may show a tail pointing in that direction.)