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Author Topic: What's your kitchen science?  (Read 398009 times)

paul.fr

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Re: What's your kitchen science?
« Reply #225 on: 17/02/2008 18:29:15 »
What you need

glass jar
plate
hot water
ice cubes


What you do


Pour about two inches of very hot water into the glass jar. Cover the jar with the plate and wait a few minutes.

Now put the ice cubes on the plate.

What happens?


Explanation:


This is how rain is made!
The cold plate causes the moisture in the warm air, which is inside the jar, to condense and form water droplets. This is the same thing that happens in the atmosphere. Warm, moist air rises and meets colder air high in the atmosphere. The water vapor condenses and forms precipitation that falls to the ground.
 

Offline DoctorBeaver

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Re: What's your kitchen science?
« Reply #226 on: 18/02/2008 08:26:46 »
What you need

a nylon comb
a water tap (faucet in the U.S.)

What to do

Adjust the tap so that it produces a small stream of water about 1/16 inch (1.5 millimeters ) in diameter.

Comb your hair. Slowly bring the teeth of the comb near the stream of water, about 3 inches (8 cm) below the tap.

What happens?

Try experimenting with different combs, or with more water flowing.

Explanation

Static electricity. When you comb your hair, a charge builds up in the comb and in your hair (this is the same charge that lets you stick balloons to the wall after rubbing them on clothing). This charge attracts the molecules in the stream of water and causes it to bend towards the comb.
 

paul.fr

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Re: What's your kitchen science?
« Reply #227 on: 18/02/2008 10:44:33 »
Thanks for the contribution, Doc. I hope you have more to come...and similar contributions from other members would also be nice.

Carrying on with the meteorology related experiments.

What you need


small paper bag and a hard surface


What you do


Blow into the paper bag and close tightly to trap the air inside, then smash the bottom of the bag against a hard surface, without letting go of the bag.

What happens?

Explanation
This is how thunder works. Air rushing out of the bag makes a loud noise. The same thing happens with thunder. Air rushes out of clouds after being heated by lightning. This causes the booming sound.
 

paul.fr

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Re: What's your kitchen science?
« Reply #228 on: 19/02/2008 10:27:24 »
What you need


Tall drinking glass, or can with paper removed
Thermometer
Ice cubes
Warm water
Water at room temperature (let it sit for a while)


What you do
 
Put the room temperature water into the glass and add ice, stir with the thermometer until you notice a film of moisture forming on the outside of the glass. Record the water temperature.

Remove the ice and trace your finger on the outside of the glass to make a mark in the moisture. Now raise the temperature of the water slowly, by adding warm water and stirring with the thermometer. Raise the temperature to a point where no moisture forms in the cleared area you marked earlier. When this happens, record the temperature of the water.




Calculate the temperature that is halfway between the two temperatures you recorded, this should be the (or never near to) the dew point temperature of the air.

You can repeat the cooling and warming process several times to see if the results are consistent.

Explanation
This demonstrates 'dew point'.
What is dew point? All air has water vapour in it and warm air holds more than cooler air. When air holds as much water as it can it is said to be saturated. The temperature to which air must be cooled to reach its saturation point is its dew point temperature i.e. 100% humidity. At this point there is a balance between evaporation and condensation. Any cooler and the water vapour will condense as precipitation of some sort. Any warmer and more water will evaporate into the air.
 

lyner

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Re: What's your kitchen science?
« Reply #229 on: 19/02/2008 22:27:09 »
Coupled pendulums.
This is a magical demonstration.
You stretch a piece of string between two supports (as taught as possible Two chairs with people sitting in them will do.
You make two pendulums, using potatoes and string (the victorian parlour trick involves potatoes but anything will do). Get them the same length - the more equal the better effect - and tie them to the horizontal string.
Have one pendulum stationary and start the other. The first pendulum will gradually slow down and the other will build up until the first is stationary. the process will reverse. The rate of changeover depends on the amount of 'coupling' between the two pendulums - the support string twists a little and transfers energy from one to the other.
This has interesting connections with quantum physics and many other resonance phenomena.
« Last Edit: 19/02/2008 22:40:17 by sophiecentaur »
 

paul.fr

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Re: What's your kitchen science?
« Reply #230 on: 21/02/2008 07:47:58 »
What a great experiment, Andrew.

what you need

pencil
paper
scissors
a drawing pin
thread, a coat hanger or piece of dowelling
a lamp


what you do


Draw a spiral on the piece of paper and cut it out carefully, it should look like a long snake. Use the drawing pin to poke a small hole in the middle of the spiral and thread the thread through this hole. Tie a knot in the end to hold it together. Attach the other end to the coat hanger or dowelling and hold the spiral above the lamp

What happens?


explanation
As warm air moves upwards from the lamp it pushes against the underside of the spiralnand makes it spin.
This is how wind works. As warm air rises the air pressure underneath it falls and cooler air nearby moves in to take its place. This sideways moving air is wind.
 

paul.fr

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Re: What's your kitchen science?
« Reply #231 on: 21/02/2008 15:56:37 »
what you need

A mirror
clouds


what you do

Place the mirror on a flat area in your garden, or pavement. look at the clouds through the mirror.
What happens?

Explanation
When you Look at the clouds in the sky, you only have other clouds to compare their movement to. If they are all moving in the same direction, they seem to be sitting still (or moving very slowly). If you are looking at their reflection in the mirror, you have the edges of the mirror as a reference point.
This is (roughly) how a Nephoscope works, this is instrument for measuring the altitude, direction, and velocity of movement of clouds.

Why not try looking at the moon through your mirror, does it look to be higher in the sky, or moving quicker?
« Last Edit: 21/02/2008 16:03:16 by paul.fr »
 

Offline JimBob

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Re: What's your kitchen science?
« Reply #232 on: 21/02/2008 22:59:20 »
 
What you need

A glass
Water
A straw
 
What you do

Suck some water up a straw and then put your thumb over the end that is in your mouth. Now keeping your thumb over the straw take it out of the water. What happens?
Now take your thumb off the end. What happens?

Explanation:
This experiment is all about the forces acting on the liquid. One of these forces is gravity, the force which pulls all objects towards the centre of the Earth. Gravity is pulling the water in the straw down towards the Earth, so why doesn’t the water fall out of the straw when your thumb is on top?

There must be another force, stronger than gravity, pushing upwards on the water. This force comes from air pressure. Air pressure is caused by molecules of air pushing against things. Air pressure is very strong and very important. It affects the weather, and the weight of all the air above us in the atmosphere pushing down is a very large force.

When the straw is just sitting in the glass there is nothing separating the air in the atmosphere from the air in the straw. This means that the air in the atmosphere and the air in the straw are pushing down on the water in the glass with the same force. When you suck on the straw it makes the water move up the straw. If you put your thumb over the end it traps the water in the straw, and your thumb separates the water in the straw from the air pressure of the atmosphere. If you pull the straw out of the water and keep your thumb over the end, the water stays in the straw. This is because there is no air pushing the water down from the top of the straw where your thumb is, but the air in the atmosphere is still coming up the open end at the bottom of the straw and pushing up against the water to keep it in the straw. The force from the air in the atmosphere pushing up is stronger than gravity pulling down! If you remove your thumb from the end of the straw the water will flow back out. This is because without your thumb there, the air is pushing with the same force from both ends of the straw. These two pushes cancel each other out so that gravity can pull the water down to the Earth, just as it was trying to do all along!
 

paul.fr

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Re: What's your kitchen science?
« Reply #233 on: 22/02/2008 09:31:51 »
what you need


two identical glass jars
four cups of cold water
ten ice cubes
one clear plastic bag
a thermometer


What you do


Split the water and the ice cubes evenly between the jars, and wrap one jar in the plastic bag. Leave both jars out in the sun for an hour.
Measure the temperature in each jar

What happens?

Explenation
In reality, sunlight passes through the atmosphere and warms the Earth’s surface. The heat radiating from the surface is trapped by greenhouse gases (the greenhouse effect.)
In this experiment, the plastic bag acts as the layer of greenhouse gases, trapping heat in the jar and causing the water to become warmer in the jar wrapped in the bag.
 

paul.fr

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Re: What's your kitchen science?
« Reply #234 on: 23/02/2008 14:27:20 »
What you need

a large mirror
a dark room
nylon tights/stockings


What you do


Stand in a dark room in front of the mirror and rub the nylon stockings together.
What happens?
Do the same with the wool jumper
What happens?


Explanation
Tiny sparks of static electricity fly back and forth between the two sides of the fabric. When you rub the fabric together electrons build up in one place. When there are lots in the same place, some jump and give off a static charge. This is when you see the spark.

This is how lightning works. On hot and humid days warm, wet air moves upwards very quickly. It forms clouds and the temperature inside the clouds falls. This fast moving air causes an electric charge to build up inside the cloud until the cloud can no longer hold it. The electricity discharges which causes the lightning flash.
« Last Edit: 23/02/2008 14:30:42 by paul.fr »
 

Offline Make it Lady

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Re: What's your kitchen science?
« Reply #235 on: 23/02/2008 21:09:00 »
If you love all these you are going to die when you see this website.

www.planet-scicast.com

It is full of kitchen science u-tube style films. Search for vacuum cleaner bazooka. Some of them have instructions. Happy experimenting.

Heres one from me:

What you need:

Energy saving light bulb
balloon
Dark room
very woolly jumper

What to do:
Stand in the darkened room. Rub the balloon on the wool jumper and charge it up. bring the balloon close to the light bulb and it should light up just for a moment. With practice and a lot of rubbing you should be able to get the bulb to light up brighter and for a longer period. It looks a little like you have super powers and is a great trick to show the kids whilst reading ghost stories.

Wa Ha Ha Haaaa!
 

paul.fr

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Re: What's your kitchen science?
« Reply #236 on: 06/03/2008 16:26:15 »
Well it's nearly C.S.I. Friday, so how about a few forensic related experiments.

This one is based on Forensic Osteology, the science of bones, and will show how you can determine someones height using their foot!

What you need


Yourself, or a friend
A ruler or tape measure


What you do


With your socks and shoes off, measure the length of your foot, from heel to toe. Next we will compare that measurement to the length of your forearm. If you measure from your elbow to your wrist, you should find that the distance is pretty much the length of your foot.

If you take the length of your foot and multiply it by 7, that should give you a distance very close to your height. If you are under 20 years old, then this may not work. This is because your bones are still growing.

The length of your foot is also the height of your head, from your chin to
the top of your head.

So, from just a few bones a forensic scientist can make some pretty accurate measurements and conclusions.
Why not try it with your friends and family.
 

Offline Make it Lady

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Re: What's your kitchen science?
« Reply #237 on: 06/03/2008 17:34:52 »
Oh Paul I love this one. I once convinced a year 7 pupil that one of the past teachers had really been killed and we had found the bones to examine. The bones were plastic prop.s but this poor kid was convinced it was all real. All these kitchen experiments work so much better if you weave a little story around them. But take care of young gullible children.
 

paul.fr

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Re: What's your kitchen science?
« Reply #238 on: 07/03/2008 07:44:29 »
Quote
Posted by: Make it Lady 
Insert Quote
Oh Paul I love this one. I once convinced a year 7 pupil that one of the past teachers had really been killed and we had found the bones to examine. The bones were plastic prop.s but this poor kid was convinced it was all real. All these kitchen experiments work so much better if you weave a little story around them. But take care of young gullible children.

Me too.


What you need

A shoe or foot
A plastic container, about the size of a shallow ice-cream tub.
Plaster of Paris
Mixing spoon
A mixing bowl
Enough moist sand or moist soil to cover the bottom of the container
Rubber gloves


What to do

Put the gloves on and put the sand or soil into the plastic container, and make an imprint of your shoe or foot in the damp sand. If you are not happy with the result, just smooth the sand back over and try again.

Mix up some plaster of Paris until it is nice an creamy, then pour the plaster mixture into the footprint impression. Leave the plaster for about an hour and a half to dry. Once the plaster is dry, remove the cast from the sand. Gently brush off any excess sand.

Why not link this with yesterday's kitchen science. You have a foot cast, can you predict how tall the person was who left the foot print? Is this the print of your suspect, the victim or someone unknown?
 

Offline Make it Lady

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Re: What's your kitchen science?
« Reply #239 on: 07/03/2008 19:09:28 »
What about writing a letter saying that you are being black=mailed by the victim and you think you have found a way to stop it. (In other words MURDER THEM!!!)
If you write with an ink pen you can do chromatography on a sample of ink that came from the letter and different types of ink that came from the suspects pens. They have to find out who's pen wrote the letter.
 

paul.fr

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Re: What's your kitchen science?
« Reply #240 on: 08/03/2008 07:16:20 »
What about writing a letter saying that you are being black=mailed by the victim and you think you have found a way to stop it. (In other words MURDER THEM!!!)
If you write with an ink pen you can do chromatography on a sample of ink that came from the letter and different types of ink that came from the suspects pens. They have to find out who's pen wrote the letter.

Yes, but first you will need to tell us how to do it. In the meantime, we need to get some fingerprints from that glass we suspect had poison in it.

What you need


Large ziplock bag
Tube of superglue
Drinking glass


What you do



Place the glass into the bag. Make sure you touch the surface using the pads of your fingers, leaving a nice smudge free print.
Lay the bag flat on a counter or work surface and squeeze a few drops of glue into the bag. Do not glue the glass to the bag, now seal the bag tightly and wait a day or so for the prints to develop. You can speed the process  time up by introducing a lamp near the bag, the heat from the lamp should quicken the process.

Explanation
The vapours from the superglue will build up in the bag and crystallize on the fingerprints. A day later, you will see starchy white fingerprints on the surface of the glass.
 

Offline keydetpiper

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Re: What's your kitchen science?
« Reply #241 on: 09/03/2008 16:33:03 »
What you need
A good-natured and relatively flexible friend
A wall

What you do
Have your friend bend over and touch his toes (or try at least). No problem! Now ask him to stand with his back and heels against the wall and bend over to touch his toes. Can't do it, no matter how strong or flexible!

What happens
Barely noticeable when someone does it in a room, bending over requires a slight backward shift of the hips. The moves the body's center of mass above the feet, and if the center of mass is above the feet your friend stays upright. With the wall, your friend can't shift his hips backwards, so the center of mass can't move to be over the feet. The result is a rather rather clumsy looking friend.

A variation is to have your friend stand sideways with his right shoulder and right foot against the wall, the tell him to pick up his left foot (the one away from the wall).
 

Offline DoctorBeaver

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Re: What's your kitchen science?
« Reply #242 on: 09/03/2008 20:29:57 »
Alka-Seltzer rocket
You will need:-
Empty film canisters or similar
Alka-Seltzer tablets
Teaspoon
Water

Method:-
Remove the canister lid and put 2-3 teaspoons of water into the empty canister
Break off a quarter of an Alka-Seltzer tablet and put it in the lid
Tip the quarter tablet into the canister and shut the lid tightly
Shake the canister for a few seconds and place it lid-down on a flat surface
Stand well back for this one!

If you are a minor, please make sure an adult is present and get permission from your parent or guardian before beginning this experiment.
 

Offline Make it Lady

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Re: What's your kitchen science?
« Reply #243 on: 09/03/2008 21:30:57 »
You can also use a fizzy drink as fuel of vinegar and bi-carbonate of soda. The latter launches quicker so you have to be very quick.
Note: The film canister must have an internal seal or it won't work.
 

Offline DoctorBeaver

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Re: What's your kitchen science?
« Reply #244 on: 09/03/2008 23:10:18 »
You can also use a fizzy drink as fuel of vinegar and bi-carbonate of soda. The latter launches quicker so you have to be very quick.
Note: The film canister must have an internal seal or it won't work.

I tried it earlier with an aspirin bottle (a plastic 1) and it worked.  [B)]
 

Offline daveshorts

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Re: What's your kitchen science?
« Reply #245 on: 10/03/2008 13:59:38 »
Lemon juice is generally slightly less violent than vinegar, but it still has a tendency to blow up in your face if you overegg it
 

paul.fr

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Re: What's your kitchen science?
« Reply #246 on: 10/03/2008 14:46:19 »
I tried it earlier with an aspirin bottle (a plastic 1) and it worked.  [B)]

We used to do this in shopping centres, back in they day when all you got was a clip round the ear from a "friendly" policeman. I reckon you could get locked up now.
 

paul.fr

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Re: What's your kitchen science?
« Reply #247 on: 10/03/2008 14:58:39 »
Whilst we wait for Sharon to tell us how to determine which pen was used on the blackmail letter, we best start lifting some fingerprints.

What you need


Fingers
Friends
An assortment of drinking glasses
Cocoa powder
A small artists brush
A magnifying glass
Inkpad
White paper, one sheet per person


What you do

Give everybody a glass and a sheet of paper, make sure the glass is clean and has no marks on it. Everybody needs to make a finger or thumb mark on the rim of the glass.

Once this is done, swap glasses (being careful to touch only the base of the glass. Don't smudge the prints that are already there.) Using the brush, place a small amount of cocoa powder over where the prints were  made. lightly dust over the prints to help make them a bit clearer.

On sheets of paper get each person who left a print originally to make another print - but this time they have to press their finger or thumb in the inkpad first.

Match these new prints to the ones you dusted for earlier. Use the magnifying glass to help you inspect them even more closely and try to match them up.

Who left which prints? Who wrote the blackmail letter?


Explenation

No two fingerprints are the same, even twins will have differences in their prints.

When you examine a print you'll notice the lines occur in one of three characteristic patterns, known in the biz as 'arches'. 'loops' and 'whorls'.

When you come to compare the chocolate and the ink prints you should get an exact match between pairs. But although two different people may have the same fingerprint type (eg. both have loops on the same finger), there will always be other little differences between individuals. That's because it's not the shape of the print that’s unique, but rather the number, location and shape of specific ridge characteristics...

What you were lifting with the cocoa powder are called 'latent' prints. These prints are formed by oil and sweat from a person's fingers when they touch a surface - the sweatier you are the clearer they’ll be (so remember to wash after being sweaty)! They're invisible to the naked eye, which is why they need some kind of treatment to help you see them.

Topic link/s
What causes "fingerprints", and why do we all have different ones?
Fingerprints
How Identical are identical twins ?

 

paul.fr

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Re: What's your kitchen science?
« Reply #248 on: 29/03/2008 22:15:23 »
What you need


 Red food colouring or joke / stage blood
 Dropper
 Small beaker
 Plain Paper
 Ruler
 Metre rule / tape measure



what you do



Lay out some paper to protect the floor, then place the paper you?ll drop the blood onto on top of them. Hold the dropper 10 cm above a clean sheet of and drip one drop of blood onto the sheet., now measure the distance of the spatter, making sure to write down the height it was dropped from and the diameter of the splatter.

Drop the blood from 20cm higher each time until you get to 200cm or higher if you wish (you can go up in larger or smaller amounts depending on how much time you have). Measure the diameter of the spot and write it down as well as the height it was dropped from.

Use a new piece of paper to drop the blood on every time you change height (this will avoid confusing results), and make sure you?re measuring the distance of the splatter each time you drop the blood.

Once you?ve done this, get someone else to do a splatter at a distance of their choosing (it can be any height within the range of the distances already dropped i.e. 10cm to 200cm). Make sure whoever conducted the test originally can?t see the random drop, because their task now is to work out what height it was dropped from by measuring its splatter and comparing it to their results from before.

If they have recorded their results accurately, then they should be able to make an 'educated' guess what height the random drop was dropped from.


what happens?

This type of forensic analysis is called Bloodstain Pattern Interpretation, or Blood Splatter. What we?re trying to do is re-create the circumstances in which a crime may have been committed.

Once you know about the different ways that blood splatters, and can recognise certain signs, you can begin to work out what happened. It does require some specialist training though.

The specialist will try to determine what the position and shape of the spatter indicate. They take measurements to determine the trajectory as well as carrying out carefully controlled experiments.

These experiments will use materials very similar to those found at the scene, because blood reacts differently depending what surfaces are involved. For example it will behave one way when it hits a carpet, and another when it hits a tiled floor. Using the results of the experiments, investigators can try to reproduce what has happened.


explenation

 Shedding of blood is the dramatic accompaniment to murder committed by violent means. Blood accounts for about 9 per cent of a healthy person's body-weight and as many murderers have discovered to their cost, when it is spilled a little goes a long way.  Once blood is shed in any quantity, and especially when it starts to clot, it becomes very difficult to deal with. Murderers' attempts to clean up after their violent handiwork often fail because of blood-traces which adhere tenaciously to their clothing or to the murder weapon. Blood found at the scene of the crime has trapped many killers who thought they removed all incriminating traces. A sensational demonstration of this was provided by the French detective Gustave Mace in 1869, when he was interrogating a murder suspect in the room which he believed had been the scene of a ghastly crime involving the dismemberment of the victim. Convinced that a great deal of blood must have been shed, Mace looked about the room but could see no obvious traces.  Then he noticed a marked hollow in the tiled floor. With the suspect looking on in astonishment, the detective took a jug of water and tipped the contents on the floor - the water collected in the hollow area, and when the tiles were lifted their under-surfaces were found to be caked with dried blood. This discovery led to a murder confession by Pierre Voirbo and to a triumph of detection for Mace.

Blood is important forensically, and can yield a great deal of information to the investigator. The first task in examining suspicious stains is to determine whether they are blood, and if so, are they human? Once this is established stains are examined for age, sex and blood group. The shape and pattern of liquid blood-splashes can help in reconstructing the murder; bloody fingerprints and palm-prints tell their own story; dried blood on a suspect's clothing can be related to the victim, the crime scene and the murder weapon; blood and tissue forced under the fingernails of the victim during a violent struggle can be linked to the assailant.

Thus a single blood-trace can provide a wealth of information, and analytical techniques are improving all the time. Blood dynamics is important not only for narrowing suspicion on the guilty but also in showing a suspect's innocence. As in many other aspects of forensic investigation, bloodstains are taken into account with a variety of other evidence to build up a pattern of crime.

The investigation of blood at a crime scene can be broadly divided into a biological approach (serology) and a physics approach (blood splatter or bloodstain pattern analysis). This fact file will concentrate on the dynamics of blood evidence.

Examination and interpretation of bloodstains on and around the body, and of blood-spots, splashes and smears at the scene of the crime, are an essential part of a murder investigation. The position and appearance of blood marks on the body and its immediate surroundings will help the investigator to reconstruct the crime.

The theory behind bloodstain pattern analysis is simple: blood is a fluid and will respond accordingly to the laws of physics. Though rarely the dominant piece of evidence in an investigation, bloodstain pattern analysis can be important in the difficult process of reconstructing a violent crime.

Experts begin by taking note of a few key variables:

    * spot size
    * quantity
    * shape
    * distribution
    * location
    * angle of impact
    * target surface

A great deal can be gleaned from the shape of blood spots and splashes found on surfaces such as floor, walls, ceiling, woodwork and furniture. The French criminologist Alexandre Lacassagne noted the correlation between the shape of blood sports and the position of the victim. Blood dropping vertically on to a flat surface form a circular mark with crenated edges, and denotes that the source was stationary at the time. Drops of blood falling from a moving object hit a flat surface obliquely and leave a spot shaped like an exclamation mark. An examination of the shape of obliquely falling blood splashes yields information about the direction and speed of impact. Such evidence helps determine the positions of victim and murderer at the time of an assault, and may also indicate the manner of violence and type of weapon used.

A line of blood spots on the ceiling of a room in which violent murder has been committed is likely to have been made by the killer wielding an axe or bludgeon in an area over his head. Smears and trails on the floor may be produced by a wounded person crawling about or by an assailant dragging the body of his injured victim. Smudges and smears on furniture and doorsteps leaving bloody fingerprints or palm prints may result from similar activities. Blood smears tend to start as drops which become ragged at one edge, indicating the direction of travel.

Large spots - the blood was travelling at a relatively low velocity.
   

Small spots - the blood was travelling at a relatively high velocity. (More force equals smaller splatter)
   

Elongated drops - victim was moving, their speed relative to the amount the spots are stretched and how far they are spaced apart. (Also indicates directionality)
   

Contact - large stain on a surface caused by contact with a bloody object.

Void in otherwise uniform splatter - something blocked the blood spray.
   

Cast-off - straight, elongated lines of splatter indicating that blood was thrown by a moving object in a change of direction. (Can show how many times a victim was struck)


Even when the blood stain is not evident it may still leave a tell tail fingerprint. To detect invisible blood stains, the luminol test is used, which is a chemical sprayed on carpets and furniture which reveals a slight phosphorescent light in the dark where bloodstains (and certain other stains) are present.

What is the luminol test?

The specialist will try to determine what the position and shape of bloodstains at the crime scene indicate. He/she take measurements to determine the trajectory as well as execute carefully controlled experiments. These experiments will use surface materials like those found at the scene to try to reproduce what has happened.

A leading authority on blood stain interpretation gives the following tips to investigators:

    * It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. In other words, the shape of the stain tends to change depending upon the angle of impact which caused the stain. For example, the more the angle decreases, the more the stain is less circular and more long.
    * Surface texture is one of the key components in determining spatter type. The harder the surface is, the less spatter will result. It is therefore extremely important to duplicate the surface in a controlled test.
    * When a droplet of blood hits a surface which is hard as well as smooth, the blood usually breaks apart upon impact. This in turn causes smaller droplets. The smaller droplets will continue to move in the same direction as the original droplet.

One of the classic murder cases in which blood evidence played an important, if controversial part was the trial of Dr Sam Sheppard. The doctor's wife was found dead in their Cleveland Ohio, home in July 1954. Her body, with the head brutally battered by over thirty blows from a heavy object was found in the master bedroom. The room, which had been ransacked, was heavily spattered with blood, and a trail of stains led down the stairs and out on to a terrace.

Dr Sheppard, who had been awakened from sleep on the living room sofa by his wife's screams, claimed to have been knocked unconscious by an intruder as he rushed upstairs. His behaviour was judged to have been suspicious, and there was considerable prejudice against him, not least on account of his alleged infidelity. He was sent for trial and found guilty of second degree murder, for which he was sentenced to life imprisonment. The coroner had made much of bloodstains on the pillow in the murder room, and a bloody imprint which he suggested had been caused by a surgical instrument which had served as the murder weapon. This instrument was never specified, but the imputation was plain that Sheppard, himself a doctor, had used it to murder his wife. The murder room abounded in blood evidence which if properly examined would have led to other conclusions. It was left to Dr Paul Leland Kirk, Professor of Criminalistics at Berkeley, to make a thorough assessment of this evidence several months later in order to reconstruct the murder. As the bedroom ceiling showed no traces of blood, Kirk reasoned that the murder weapon had been wielded in a more or less horizontal fashion. This was borne out by the state of blood splashes on the walls, some of which had been flung from the murder weapon as it was swung backward and forward to make contact with the victim's head. Other blood spatters had come directly from the battered head. The Professor carried out experiments which suggested the most likely weapon to have caused the pattern of blood splashes was a heavy flashlight. He also judged that the murderer stood between the twin beds, having noted blood drops which had been smeared into streaks on the right side of the victim's bed. This interpretation was supported by blood free areas on two of the walls behind the murderer which had been protected from flying blood spatters by his body. A killer standing in that position must have swung the murder weapon with his left hand - Dr Sheppard was neither left-handed nor ambidextrous.

By implication, the murderer must have been thoroughly spattered with blood. Yet apart from a bloodstain on the knee of Sheppard's trousers, which got there when he stood close to the bed to take his wife's pulse, there was no evidence of other blood staining on his clothes A number of factors similarly pointed away from Dr Sheppard as the murderer - it was certainly the case that the examination of the blood evidence had been bungled in the first instance. There was no better illustration of this than the admission during a second trial that the trail of stains leading from the bedroom through the living room and out on the terrace had not even been properly tested for human origin, nor was blood groupings attempted. Professor Kirk's interpretation of the blood evidence went a long way towards securing Dr Sheppard's eventual freedom.

Film and television aficionados may recognise the recognise in this case the opening premise of The Fugitive. Obviously the series would have been a lot shorter with the help of a good bloodstain expert.

Some common terms used in bloodstain pattern interpretation.

    * Angle of Impact  --  The acute angle formed between the direction of a blood drop and the plane of the surface it strikes.
    * Cast-Off Pattern  --  A bloodstain pattern created when blood is released or thrown from a blood-bearing object in motion.
    * Drip Pattern  -- A bloodstain pattern which results from blood dripping into blood.
    * Flight Path --  The path of the blood drop, as it moves through space, from the impact site to the target.
    * Flow Pattern  --  A change in the shape and direction of a bloodstain due to the influence of gravity or movement of the object.
    * Impact Pattern  --   Bloodstain pattern created when blood receives a blow or force resulting in the random dispersion of smaller drips of blood.
    * Misting  --  Blood which has been reduced to a fine spray, as a result of the energy or force applied to it.
    * Projected Blood Pattern  --  A bloodstain pattern that is produced by blood released under pressure as opposed to an impact, such as arterial spurting.
    * Spatter  --  That blood which has been dispersed as a result of force applied to a source of blood.  Patterns produced are often characteristic of the nature of the forces which created them.
    * Target  --  A surface upon which blood has been deposited.
    * Transfer/Contact Pattern  --  A bloodstain pattern created when a wet, bloody surface comes in contact with a second surface.  A recognizable image of all or portion of the original surface may be observed in the pattern.
    * Wipe Pattern  -- A bloodstain pattern created when an object moves through an existing stain, removing and/or altering its appearance.

Forensic Serology



 

paul.fr

  • Guest
Re: What's your kitchen science?
« Reply #249 on: 06/04/2008 15:27:51 »
What you need

a drinking glass
ice


what you do


Outside on a cold day you often see your breath turn into a white mist that looks somewhat like a cloud, but why? and can we duplicate this effect?

Take a short glass or plastic cup and put ice in it, filling it no more than halfway, then gently blow across the top of the glass or even slightly down into it until you see your breath making a white mist. If you are unable to see a white mist sprinkle some rock or table salt into the ice, mix it up a little and and then try blowing across the top of the glass again.

explanation
This happens because your breath is warm and it can hold more water vapor than the cold air outside. Some of the water vapor in your breath quickly condenses out into tiny water droplets that you can see.
topic link/s


 

The Naked Scientists Forum

Re: What's your kitchen science?
« Reply #249 on: 06/04/2008 15:27:51 »

 

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