Download Fundamental Forces of the atom

"Now I am become Death, the destroyer of worlds."
Robert Oppenheimer after the first test of the atomic bomb.
Elementary Particles
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By the mid - 1930s,
experimental evidence
confirmed the existence
of three sub-atomic
particles.
These are protons,
electrons, and neutrons.
The Four Forces of Nature

The four basic
forces of nature
are
electromagnetism,
gravity, strong
nuclear force, and
the weak nuclear
force
The Strong Force
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
This force is
responsible for
holding the nucleus
together.
This force is so strong
that it binds and
stabilizes the protons
of similar charges
within a nucleus.
However, it is very
short range. No such
force will be felt
beyond the order of 1
fm (femtometer or 1015 m).
Electromagnetic Force
This is the force which
exists between all
particles which have an
electric charge.
 For example, electrons
(negative charge) bind
with nucleus of an
atom, due to the
presence of protons
(positive charge).
 The force is long range,
in principle extending
over infinite distance.
 However, the strength
can quickly diminishes
due to shielding effect.

Electromagnetic Force continued
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Many everyday
experiences such as
friction and air
resistance are due to
this force.
This is also the
resistant force that we
feel when pressing our
palm against a wall.
This is originated
from the fact that no
two atoms can occupy
the same space.
Electromagnetic Force 3
its strength is about 100
times weaker within
the range of 1 fm,
where the strong force
dominates.
 But because there is no
shielding within the
nucleus, the force can
be cumulative and can
compete with the
strong force.
 This competition
determines the stability
structure of nuclei.

The Weak Force



This force is
responsible for nuclear
beta decay and other
decay processes
involving fundamental
particles.
The range of this force
is smaller than 1 fm
and is 10-7 weaker than
the strong force.
It is important in
understanding the
behavior of
fundamental particles.
Gravitational Force





This is the force that
holds us onto the
Earth.
It is important in our
daily life.
On the scale of the
atomic world it is of
negligible or no
importance at all.
Gravitational force is
cumulative and
extended to infinity.
It exists whenever
there is matter.
Gravitational Force

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
Your body is experiencing
a gravitational pull with,
say, your computer (or
anything close to you or
as far away as stars and
galaxies) but the effect is
so small you will never
sense it.
However, you can sense
the gravitational pull with
the Earth (that is, your
weight).
This is due to the
cumulative effect of
billions of billions of the
atoms that make up your
body with those atoms of
the Earth.
Gravitational Force 3


This means that the
larger the body
(contains more
matter), the stronger
the force.
But on the scale of
individual particles,
the force is extremely
small, only in the
order of 10-38 times
that of the strong
force.
Familiar and unfamiliar Forces



Of the 4 basic forces
two of them can be
experienced in our
daily life.
They are also called the
familiar forces which are
the electromagnetic
and gravitaional forces.
Similarly, the strong
force and the weak
force are called the
unfamiliar forces.
Mystery of the Forces
How do the forces
work?
 Why do we sense forces
- pushing and pulling?
 The basic forces
between particles of
matter all act through a
'force carrier', which is
exchanged between the
interacting particles.
 These exchange carriers
are also known as field
particles, or gauge boson

The Strong Force Carrier: Gluons (g)

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Gluons have no mass
and no electric
charge.
They carry a special
'charge-like' property
that hold quarks
(constituents of
protons and
neutrons) together.
The theoretical
treatment of this
carrier is described in
the theory of quantum
chromodynamics
(QCD)
The electromagnetic force Carrier: Photons (g)
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Photons are responsible to
'carry' electromagnetic
forces.
It is also known as the
particle of 'light' as they also
'carry’ the light that we see.
They have no mass, and no
charge and can exchange
between two particles over
infinite distance.
This is also the reason why
light can travel to infinite
distance and we can see
stars that are far away.
Detailed theoretical
description of photons is
given in quantum
electrodynamics (QED).
The weak force Carrier: W and Z (W+, W-, Z0)

The carrier W can be
either positively
charged (W+) or
negatively charged
(W-), while Z is
neutral (Z0). The
reason why the force
is weak is because
these carriers are
massive, about 100
times that of the
weight of a proton.
The gravitaional force Carrier: Graviton (?)
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The existence of
this carrier is yet to
be confirmed.
If it exists it should
have zero mass and
zero charge.
It may will be the
discovery of the
century if its
presence is ever
detected.
Antiparticles



Particles have their
antiparticles.
Antiparticles are
produced in nuclear
reactions when
enough energy is
available.
When an antiparticle
and a particle meet
they annihilate each
other.
Fate and origin


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The energy of their vanished
mass along with any kinetic
energy they possessed is
converted to electromagnetic
energy.
Antiparticles are extremely
rare in nature; they are
mostly produced in particle
accelerators.
This picture shows the Large
Hadron Accelerator located
between France and
Switzerland.
People use magnetic and
electric fields to accelerate
protons and have them
collide.
These collisions result in
many new subatomic
particles.