Introduction to
Forensic Physics
 Physics

Physics
in Forensics
is
phenomena
the
science
such
momentum,
as
that
deals
motion,
light,
with
natural
work,
energy,
electricity,
and
force,
sound,
magnetism.

A
forensic
behind
at
physicist
an
happened
and
scientist
must
motion)
and
and
how
these
can
accident
who
was
understand
especially
quantities
happened in a collision.
use
scene
at
the
to
fault.
kinetics
Newton's
can
be
evidence
determine
To
do
(the
laws
used
what
this
the
study
of
of
to
left
motion
tell
what
Let's start with some basic terms used in physics
Force:
Force is an external agent capable of changing the state of rest or motion of a particular body. It is
a push or a pull.
Weight and mass:
Weight is a force acting on that matter . Mass resists any change in the motion of objects. In
physics, the term weight has a specific meaning - which is the force that acts on a mass due to
gravity. Weight is measured in newtons. Mass is measured in kilograms.
Weight = mass x acceleration due to gravity = mg
Mass is a measure of the amount of an object that is present.
Friction
A special type of force that causes an object to slow down.

There are
kinetic.
two

Static friction is the force that must be
overcome to start an object moving. The force
required to start a parked car moving while the
brakes are still on is static friction.

Kinetic friction is the force that slows down a
moving object and the force that causes the skid
marks left at an accident scene.

The coefficient of friction (u) is determined by
dividing the force it takes to move the object
by the weight of the object.
Friction = force/weight
types
of
friction,
static
and
Velocity

It is the speed and direction a traveling object.

The velocity of an object is the rate of change of its position with respect to a frame of
reference, and is a function of time.

Velocity (v)= distance (d)/time (t).

A
positive
with
the
object is moving.
or
velocity
negative
to
value
show
Acceleration
The increase or decrease in the velocity of an object.
Acceleration (a) = velocity (v) /time (t)
is
in
often
associated
what
direction
an
Momentum

The product of the mass of an object and its velocity. It is defines as the mass in motion.

Momentum (p) = mass(m) x velocity(v).
Energy

Energy is the ability to do work.

There are two types of energy, kinetic and potential.

Kinetic energy is the energy of motion. Kinetic energy = 1/2 (mv2).

Potential energy is the energy of position.

Potential energy = mass x acceleration of gravity X height = mgh.

Newton’s
three
constant
motion,
as
how
balanced
these states of motion.
laws
and
and
of
motion
explain
accelerated
motion,
as
unbalanced
forces
act
to
rest,
well
cause

Newton’s first law of motion states that an object at rest will remain at rest,
and
an
object
in
motion
will
remain
in
motion
until
acted
upon
by
an
outside
source.
Newton
called
this
tendency
of
objects
to
remain
in motion or stay at rest Inertia.

Newton’s second law defines a force to be equal to the change in momentum
with a change in time. F= ma or F= dp/dt. p=mv= F= d(mv)/dt=mdv/dt= ma

Newton’s third law of motion states that for every action, there is an equal
and opposite reaction.

Work is a force acting through a distance. Work = force x distance.

Density is the mass of an object divided by its volume. Density can be used to identify types of
glass found at crime scenes and to match to
possible subjects. ρ = m/V

Power is the rate at which work is done. Power = work/time.