Physics in Forensics
In Forensic Investigations, one way physics is used to determine the velocity of weapons. To determine the velocity of weapons, the ballistic pendulum was invented. The ballistic pendulum was developed in 1743 for the velocity of projectiles. The principle of the ballistic pendulum is the transfer of momentum from a projectile with a small mass and high velocity to a large mass with a resultant low velocity.
In one investigation, a lady in Australia was thought to have commit suicide on a very popular cliff used for suicide. Physicist used calculations and the knowledge of the Newton's law, thermodynamics, and friction to determine that the boyfriend of the young lady threw her off of the cliff. The physicist, Rod Cross, stated that "...the police did not understand that physics could help solve the problem."
Since physics deals with motion, forensic investigators keeps that in mind when dealing with blood spatter and blood patterns. The investigators looks at the angle and length of the spatter and patterns to determine what happened. The shape of the blood drop and also reveal the direction that was traveled and the angle in while a surface was struck. A investigator by the name of Kennedy, states that "Bloodstain patterns, will help the investigators understand the positions and the means by which the victim and suspect moved, interacted, and struggled through the crime scene...".
When there is a car accident, investigators are sent to view the point of impact, final resting position, skid marks, etc. With those measurements the accident can be reconstructed and investigators are able to figure out what caused the accident and what went wrong. The Conversion of Linear Momentum is used to determine the weight of the vehicles, the angle in which of they collided, and the places they came to rest. (The Principle of the Conservation of Momentum states that: if objects collide, the total momentum before the collision is the same as the total momentum after the collision (provided that no external forces - for example, friction - act on the system).)