Consider what happens when you spill water: The liquid falls to the ground and makes a puddle. The shape and size of the puddle depends on the amount of liquid, the height of the container, and whether you spill on carpet, wood, linoleum or some other surface.
What determines the size shape and number of bloodstains?
The texture of the target surface upon which a drop of blood falls affects the size and shape of the bloodstain pattern. Hard, nonporous surfaces will produce circular stain patterns that have smooth edges, but softer, porous surfaces will produce spatter stains that are scalloped or have rough edges.
What determines the size of a drop of blood?
The drop volumes were determined by collecting and measuring the volume of a known number of drops, and so tend to be overestimates when small satellite or accompanying droplets are present.
What factors will influence the shape of a stain produced by a free falling drop of blood?
When blood is impacted, droplets are dispersed through the air. When these droplets strike a surface, the shape of the stain changes depending on the angle of impact, velocity, distance travelled and type of surface impacted.What are the 4 phases of impact?
There are four phases of impact: contact and collapse, displacement, dispersion, and retraction.
What properties of blood determine the shape of a blood drop in flight?
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. surface.
What can blood spatter analysis determine?
Bloodstain pattern analysis (BPA) is the interpretation of bloodstains at a crime scene in order to recreate the actions that caused the bloodshed. Analysts examine the size, shape, distribution and location of the bloodstains to form opinions about what did or did not happen.
What test can be used to determine if a stain is blood or not?
Phenolphthalein is a presumptive test that reacts with the heme molecule present in blood. A positive reaction gives a pink color. While bloodstains normally appear red-brown in color, the color of the substrate or the age of a stain may affect the appearance or visibility of the stain.What effect does the surface have on the diameter and shape of bloodstains?
As would be expected, a larger surface area would allow for larger drop of blood to form before falling. The height from which the blood falls will affect the size of the stain, with greater heights tending to result in larger bloodstains.
What variables can affect the size quantity and distribution of impact spatter patterns?The quantity and size of spatters produced by a single mechanism can vary significantly. The amount of available blood and the amount of force applied to the blood affect the size range of spatters. Spatter is created when sufficient force is available to overcome the surface tension of the blood.
Article first time published onWhat is the relationship between size and shape of the drop and the angle of impact?
The higher the blood drop falls from, the larger the diameter of the blood drop will be on the surface it strikes. 2. What would be the difference between a blood drop that strikes at a steep angle, compared to a relatively flat (lower) angle? The steeper the angle, the longer and thinner the blood drop will be.
How is area of convergence determined?
To find the area of convergence, investigators typically use string to create straight lines through the long axis of individual drops, following the angle of impact along a flat plane, for instance the floor or wall where the drops are found.
How does a blood drop reach its terminal velocity when falling?
Passive drop increases velocity as it falls due to effects of gravity. Velocity increases when drops fall from greater heights, however, patter will not become larger at heights above 7 feet. Droplet reaches TERMINAL VELOCITY due to friction.
How do you measure height of blood spatter?
The height of the source of blood is the side opposite the angle of impact. To solve for the height (or the side opposite the angle of impact), apply the Law of Tangents. Example: Crime-scene investigators noted blood spatter on the floor of the kitchen.
What are the different blood spatter patterns?
Bloodstains are classified into three basic types: passive stains, transfer stains and projected or impact stains. Passive stains include drops, flows and pools, and typically result from gravity acting on an injured body. … Typically, forward spatter is a fine mist and back spatter is larger and fewer drops.
What is medium velocity spatter?
A medium velocity spatter is a result of a force anywhere from five to a hundred feet per second . This type of splatter can be caused by a blunt force such as a baseball bat or an intense beating. This type of spatter is usually no more than four millimeters. This type of spatter can also be a result of a stabbing.
What does the shape of an individual drop of blood provide?
surface tension holds the drop together to form a spherical or oscillated shape, when gravity overcomes the surface tension it will cause the blood to drop, the size of the drop will determine the amount of terminal velocity, and the friction from the air is what terminal velocity is trying to equal.
What shape does a bloodstain make when it falls perpendicular 90 to a surface?
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.
How do blood spatter patterns help CSI determine the type of weapon used?
These droplets of blood have been acted on by forces other than gravity, either being cast off of a weapon, or spraying from a victim onto a surface. The shape and size of these droplets can help to determine the positioning of a victim, the type of weapon used, and the force used in the crime.
What is the shape of a drop produced from a passive drop?
Passive drops will vary in shape and size depending on the volume of blood and the surface texture, but will generally be circular.
How can you determine the direction of travel of blood droplets?
the direction of blood droplets can be determined from the shape that it forms when they hit the flat surface. the tail of the elongated drop points to the travel direction.
What are three presumptive blood tests?
Luminol, leuchomalachite green, phenolphthalein, Hemastix, Hemident, and Bluestar are all used as presumptive tests for blood.
What three 3 questions should the investigator answer when examining an apparent dried bloodstain?
What three questions should the investigator answer when examining an apparent dried bloodstain? -is it blood? -is it human or animal? -what is the blood type?
What is the name of the test that is used to determine if a blood stain is human?
How it works: The Ouchterlony test is used to determine if a blood sample is human or animal through the comparison of its reactions to specific antibodies. A sample of the unknown bloodstain is placed in a well in an agar gel.
How is area of convergence determined quizlet?
Area of convergence- The area on a two-dimensional plan where lines traced through the long axis of several individual bloodstains meet; this approximates the two-dimensional place from which the bloodstains were projected. … A common method for determining the area of origin is the string method.
Can you tell how old dried blood is?
Raman spectroscopy and advanced statistics allow the researchers to date a blood stain accurately, provided said blood stain is less than two years old. Raman spectroscopy involves shining a laser on a sample and measuring the intensity of scattered light.
Why are blood stained clothing allowed to dry completely before packing?
Stains (Wet) – Blood, Semen, Saliva Biological evidence should always be allowed to air-dry before packaging/storage. Moisture allows bacterial growth to occur, rapidly destroying nuclear material and therefore, greatly diminishing the possibility of obtaining useful DNA results.
How does velocity affect blood drop size?
Increasing velocity of the drop also causes an Increase in the diameter of the spatter in passive drops of blood. Passive drop increases velocity as it falls due to effects of gravity. Velocity increases when drops fall from greater heights, however, patter will not become larger at heights above 7 feet.
What factors affect the terminal velocity of blood?
Terminal velocity of the falling blood drop depends on its size. Smaller drops have a lower terminal velocity and acquire it after a shorter fall distance. Larger droplets accelerate over a greater distance and therefore attain a greater terminal velocity.
How does the size of ball affect the fall time and terminal velocity?
If the object is falling in air, the mass is small, and the size is large, the terminal velocity will be lower than if the mass is large and the size is small. Two reasons and an explanation: an object with small mass has smaller weight (downward force) than an object with larger mass.
What are the 3 chemicals used to find and analyze blood spatter?
Electrolytes like sodium, potassium, chloride, and calcium can also be measured in a blood chemistry analysis, along with levels of proteins and lipids. Analyzing what is in a blood sample is useful in determining the cause of death at a crime scene.
