The Role of Physics in Solving Crimes
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Physics is used in nearly every area of Forensic Science, the application of science to criminal investigations.
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Generally, physics is used mainly in ballistic study, for reverting material damage for important items (reconstitution), simulating the crime scene targeting, for example, to discover what floor of the building from which the evidence or victim was thrown.
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Gun ballistics - the trajectory of a bullet can be reconstructed using physics equations, the impact between the bullet and the target (and shooter) is analyzed using conservation of momentum. The bullet also behaves as a gyroscope while in air and follows a precession or nutation oscillatory motion. Finally, each cartridge case contains skid marks that are similar to human fingerprints (they are unique). These are photographed and studied optically to determine the type of gun that was used.
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Fluid dynamics - viscosity, surface tension, drag force and gravity all act on the blood drop from the moment it leaves the human body until a surface is reached. The ratio between the drag force and surface tension determines whether or not the blood drop disintegrates in the air, the surface tension is responsible for the spherical shape of the blood drop, the ratio between the drag force and gravity determines whether the drop will accelerate or decelerate. The maximum velocity the drop has before disintegration can be calculated. The impact between a blood drop and a surface leads to the formation of a bloodstain which is circular if the angle of impact is normal or elliptical for any other angle. For circular bloodstains, for example, the maximum spreading diameter can be computed and the spikes that appear around the edges of the bloodstains are used to determine the direction of motion of the blood source.
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Vehicle collisions - when a pedestrian collides with a car, the followed trajectory can be reconstructed, which depends on the position of the pedestrian's center of mass and the velocity of the car. In vehicle-vehicle collisions, skid marks can be used to determine the velocities of the vehicles before the impact. The amount of the energy released in the impact can be calculated. Equations of motion can also be used to tell whether a person was the driver of a car.
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Falls from heights - gravity, frictional force and air resistance act on a body in flight. We use Phys to establish whether or not a jump from a height was intentional - if a person jumped or was pushed. When a person is pushed, she/he will behave as a rigid rod and will rotate with a certain angular frequency.
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Source: https://www.quora.com/How-is-physics-used-in-forensic-science