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CSI: Who Done it?


Cvankerkhove

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Today in physics class we did a little something special; a fun activity investigating several crimes. Whether these crimes were really in the local area, or a figment of imagination, it was still interesting to pick them apart to find out the culprit. The first crime scene was a murder, murder by gun. We had to decide which gun did the killing and based on small pieces of evidence, and by knowing this gun we could match it up with certain people. We knew the initial height of the bullet (the exit wound) to be the height of the victims shoulder, and the final height the height of the hole in the wall. Using this displacement, the acceleration due to gravity, and the fact that the bullet traveled horizontally, the time could be found. Finally, using this time and horizontal displacement, we discover a velocity 30% as strong as the velocity fired, and the pieces match up.

Secondly, a body was found dead at the bottom of a hotel after Alonzo Green supposedly tried to jump to the swimming pool. We have to decide if he jumped, or was pushed. Once again, using kinematics we can find the time it takes for a person to fall the given height. The given height could be measured with a diagram and a conversion scale from cm to meters. Once we have this time, we are given  the max velocity of a 45 year old male sprinting to be 6.9 m/s, and this velocity will leave a person 2 meters short of the pool, exactly what Alonzo was. He jumped.

Lastly, Evelyn Horton drove her car off a bridge when she supposedly was sabotaged by a raging driver. However, she may be just saying this to avoid embarrassment, and so we want to know which is true before moving in to a long term investigation. Once again, kinematics are used to find the time it takes the car to fall a certain distance, and therefore allow us to find the initial velocity when hitting and breaking the rail. Horton claimed that she decelerated at least 8.83 m/s/s before hitting the rail, however, with her given initial velocity, her final velocity with this acceleration would be to slow to make it as far as she did, therefore she snoozed. 

All in all, this was a fun activity that put a spin on our daily routine in APC, and the extra credit definitely made it competitive and fun ;) 

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It's super interesting to think that kinematics can be applied to forensics! I like the very realistic application to something that we've learned in class

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It was a blast listening to the various folks talk out their reasoning, while watching others closely guard their secrets in an attempt to win the 'prize.'

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