FORCES
Kinematics
The study of how objects move
Dynamics
The study why objects move as they do.
Kinds of Forces
Gravitational Force:
Attractive force that exists
between all objects. The
gravitational force between the
Earth and the moon keeps the
moon in orbit. It may be the
most evident but it is the
weakest of all the forces.
Electromagnetic Force:
Charged particles at rest or in motion exert electric
forces on each other. They give materials their
strength, their ability to bend, squeeze, stretch or
shatter. When charged particles are in motion they
produce magnetic forces on each other. Electric and
magnetic forces are both considered to be aspects of
this single force.
Kinds of Forces
Strong Nuclear Force:
A strong force that holds the particles
of the nucleus of an atom together.
Short range attractive force that is
much larger in magnitude to the
gravitational or the electromagnetic
forces.
Weak Force:
Force involved in transmutation of particles within the nucleus.
Only observed/viewed in radioactive decay. Stronger only than the
gravitational force.
electron
neutron
proton
History Lesson
Aristotle (384-322 B.C.)
Two Types of Motion
Natural
GreekMotion
Philosopher
and scientist, student
Objects
seek their
resting of
placesAlexander the
of Plato
and
thenaturaltutor
- Boulders fall, Smoke rises
Great.Heavenly bodies move in perfect circles around the Earth
Violent Motion
Imposed Force
First Some
to external
statecausethat
i.e.. Wind a
on a force
ship
If an object is in motion
“Against its motion
nature” then some kind of force is responsible
causes
Earth not moving, is in its natural resting place
Nikolaus Copernicus (1473-1543)
Polish Astronomer who demonstrated that the Earth
rotates on its axis and that the planets revolve
around the sun
Heliocentrist – Belief in the sun centered
model of the solar system. Prior belief was
the geocentric model, with the Earth as the
center of the universe
Received his publication “ De Revolutionibus” the day he died May 24th 1543
Galileo Galilei (1564-1642)
Italian astronomer, physicist, mathematician,
and inventor
Tried and convicted of heresy for his beliefs in the
Heliocentric- Copernican model of the solar system
First to define a FORCE as a Push or Pull
Force is not necessary to keep an object in motion
So why do objects come to rest?
FRICTION
Friction is a type of force, caused by irregularities in the surface
of objects that are in contact. When friction is present a
continual contact force is needed to keep an object in motion.
Galileo believed and showed that “Experiment” not “Logic” was the best test of knowledge
Galileo’s ideas discredited Aristotle and many ancient philosophies
He died the year that Newton was born 1642
Sir Isaac Newton (1642-1727)
It Awas
during
thisEngland
timehisthat
he
family
friendin
recognized
intelligence
Born
on
and helpeda him
to get into
Trinity College,
devised
number
of
scientific
Christmas
day 1642
Cambridge University
principles that we still adhere to
today
Never knew his father, As a
young lad lived with his mother
In on
1665
thefamily
Bubonic
their
farmPlague reached
Three
LawsandoftheMotion
Cambridge
University was closed
Theory on colored light
Fluxions
Better
asa stellar
Had
Newton
few –friends
went
back
andknown
was
to hisnotfamily
farm
Calculus
student
and continued
but was very
to study
brighton his own.
The law of Gravity
Three Laws of Motion
Newton’s First Law of Motion
“Law of inertia”
An object will remain in it’s
state of motion unless a force
acts upon it.
Inertia = The reluctance of a body to change it’s state of motion.
Mass is a measure of inertia
A Body at rest `tends to stay at rest
A Body in motion tends to stay in motion
Newton’s Second Law of Motion
The acceleration produced by a net force on an object is directly
proportional to the magnitude of the net force (in the same
direction as the net force), and is inversely proportional to the
mass of the object.
F
a =m
Acceleration= Net Force/ Mass
F=ma
Newton’s Third Law of Motion
Whenever one object exerts a force on a second object, the second
object exerts an equal and opposite force on the first object.
Action – Reaction Law
Hammer & Nail
The hammer exerts a force on the nail to
drive it into the block. The nail must exert a
force on the hammer to halt it in the process
Horse and Cart
Its actually Newton’s
Second Law that
determines if the cart
accelerates
All
A horse
the forces
has some
on the
understanding
cart must be
of physics. He
identified
knows Newton’s
1.third
The law.
pull For
of the
horse
is only
every
force
applied
force
there is anone
equal
but opposite
2.
The friction between the
force.
cart and the ground is another
If
unbalanced
net force is
present
than the
cart
accelerates
So, he knows that no matter how hard
pulls
the can
cart,pull
theoncart
back
Ifhethe
Horse
the will
cartpull
more
on him
the same
force,
opposite
than
thewith
friction
applied
between
the in
direction.
forces
must
balanced.
the
cartbewill
accelerate
cart
and theThe
ground,
Hence no acceleration. So why pull?