Firstly, we learnt about height of impact. As a drop of blood falls through the air, it accelerates and theoretically, the greater the height, the greater the speed of the blood upon impact, and hence the larger the diameter of the blood stain.
This is the equation to calculate vertical distance travelled by the blood
s= ut + 1/2 at^2
s= vertical distance travelled by the blood
u= initial speed of the blood
a= acceleration due to free fall (9.8ms^-2)
t= time taken for the blood to reach the point of impact
Firstly we carried out the first experiment to see if the vertical distance really does affect the diameter of the blood stains obtained. We attached an A4 sized paper onto the clipboard and placed it on a surface. Then, we clamped the dropper to the retort stand 10 cm above the paper on the clipboard.
Next, squeeze a drop of blood to the paper below and measure the diameter of the blood drop. Repeat this to obtain 2 results and from there get the average diameter. Repeat the above steps for vertical distances: 30, 60, 100 and 150. Following that, record results in table form.
Our results showed that the greater the vertical distance, the greater the diameter of the blood stain. These were our results:
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| Table of results |
Then, we had to carry out a second experiment which was regarding the angle and direction of impact of the blood stains. We were first given some information on the angle and direction of impact in the worksheet.
Angle of impact- acute angle that is formed between the direction of the blood drop and the surface it strikes-> this is used to determine the area of convergence and area of origin.
ANGLE OF IMPACT (on flat surface) CAN BE CALCULATED BY MEASURING LENGTH AND WIDTH OF STAIN.
For example: when a droplet of blood falls to the surface at 90 degrees, bloodstain will be circular and it will be more elliptical when angle of impact increases.
elliptical- egg-shaped, rounded like an egg :0 haha.
Calculation of angle of impact:
i= sin^-1 W/L
We had to take some precautions before carrying out the experiment. For example: we had to take note that when measuring the length, L and the width, W of a stain, no part of hte spines, tails or satellite splatter are included in the measure.
Firstly, we attached A4 paper to the clipboard and placed it on the floor. Then clamp the dropper to the retort stand and place it at least 100cm above the surface of the paper. Elevate the clipboard to 10 degrees and squeeze one drop of blood onto the paper. Then, measure and record length and width. (Don't forget to label the stain- miss siow always emphasises HAHA) Repeat these steps for the other angles: 40 and 70 degrees.
Based on our results, we have concluded that the higher the angle of elevation, the lesser the angle of impact.
There were also other knowledge gained such as the velocity of impact of the blood and the surface of impact of the blood. Blood that drops on a smooth surface (smooth edges) would look different from blood that drops on a rough surface (more jagged edges)
Overall, i felt that this was quite a useful and beneficial session of CSI because i never knew that the way the blood stains were positioned or how they looked like could tell us so much about what happened at the crime scene. It gave me a more insightful outlook to this topic about blood splatter in the CSI module and it urges me to learn more as i believe that as mentioned in the first lesson, physical evidence speak alot and besides blood splatters, there may also be other evidences that can give us more in-depth and wider vision of the case such as gunshots in human bodies, or post-death changes in the dead bodies after the crime was committed.
PHOTOS:
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| Measuring the vertical distance |
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| The blood given to us |
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| Our blood splatters :) |
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