A drop deposited at a 90 degree angle of impact will be approx
. circular in shape
with no tail or buildup. As the angle deviates from 90, the stain becomes elongated in shape. Buildup will occur when angles are larger, whereas longer tails will appear as the angle becomes smaller.
When a blood drop lands on a surface at a 90 degree angle What shape is the drop in typically an oval a circle a sphere the angle makes no difference in the shape of the drop?
Explanation: Left: passive bloodstains. Right: bloody shoe print transfer pattern. Because blood demonstrates surface tension, or cohesive forces that act like an outer skin, a drop of blood dropped at a 90° angle forms a
near-‐perfect spherical shape
.
Which three drops struck the surface closest to a 90 degree angle?
Drops 1, 5, and 8
struck che surface closest to a 90-degree angle. This can be deter- mined because they are the most nearly circular of the drops, and a drop of blood striking a surface at right angles produces a nearly circular stain.
What two forces act on a falling drop of blood?
The spherical shape is caused by
the surface tension
of the blood. Surface Tension causes the blood drop to pull itself in; both horizontally and vertically. The blood drop will settle into a spherical shape, as a result of the surface tension.
What are the two most common methods for documenting blood patterns?
Name and describe two methods for documenting bloodstain patterns.
Grid method
– setting up a grid of squares of known dimensions over the entire pattern using string and stakes. All overall, medium-range, and close-up photographs are taken with and without the grid.
What is wipe pattern?
A wipe pattern is “
An altered bloodstain pattern resulting from an object moving through a pre-existing wet bloodstain
.”
What are the 4 types of passive bloodstains?
- Passive Bloodstain. Passive Bloodstain on a rough surface (such as wood or concrete)
- Projected Bloodstain. Projected Bloodstain, possibly a Cast-Off Pattern or a HVIS.
- Transfer Bloodstain.
What are the 6 patterns of blood spatter?
- 1902, Dr. John Glaister described 6 patterns: a. …
- circular drops. b. arterial gusheswalls or ceilings produced by.
- pumping action of the heart. c. splashesshaped like exclamation points;аused to.
- d. smearsleft when victim or suspect touches surface. e. …
- smears. f. poolsperson remains in one place bleeding heavily.
What are the 4 phases of impact?
There are four phases of impact:
contact and collapse, displacement, dispersion, and retraction
. The angle of impact can be seen from the presence of elongations or tails. The longer the tail, the more acute the angle of impact.
What force is responsible for holding a drop of blood together?
This procedure can be easily done because of capillary action, the ability of a liquid to flow up a small tube against gravity, as shown in Figure 7. When your finger is pricked, a drop of blood forms and holds together due to
surface tension
—the unbalanced intermolecular attractions at the surface of the drop.
What force must exceed the surface tension of blood in order for it to free fall?
The gravitational force
must exceed the surface tension of the blood in order for it to ‘free-fall’. (Surface tension is caused by the molecular cohesive forces within a compound).
What shape does a passive drop of blood at a 90 degree angle have?
When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be
circular
. Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
What are the three main types of bloodstain patterns?
Bloodstains are classified into three basic types:
passive stains, transfer stains and projected or impact stains
.
What can flow patterns tell you?
Flow Pattern- A bloodstain pattern formed by the movement of small or large amounts of blood as a result of gravity’s pull. … The photographs and sketches can also point out specific stains used in
determining the direction of force
, angle of impact and area of origin.
How can you tell the difference between a wipe pattern and a swipe pattern?
– A wipe pattern
is created
from an object moving through a bloodstain, while a swipe pattern is created from an object leaving a bloodstain. … of blood spatter onto a target surface or object.
What can transfer and wipe patterns indicate?
Swipe Pattern — the transfer of blood onto a surface not already contaminated with blood. One side is usually feathered which indicates the direction of travel. Wipe Pattern —
created when an object moves through blood that has not completely dried and moves, removes, or otherwise alters it
.
