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Transcript
A brief review.
• Force.
– A push or a pull.
• ‘Nuff said...
No longer review..
• Net force.
– The overall force on an object after all forces
are added together.
No longer review..
• Unbalanced forces acting on an object
will change the objects motion.
No longer review..
• Balanced forces on an object will not
change an objects motion.
Kind’a stupid example 1
Net Force
Net Force
Net Force
=0
Newton Rocks!
Sir Isaac Newton (1642-1727)
Sir Isaac Newton
“If I have been able to see further, it was only
because I stood on the shoulders of giants.”
As mathematician, Newton invented integral calculus, and
jointly with Leibnitz, differential calculus. He also calculated a
formula for finding the velocity of sound in a gas which was
later corrected by Laplace.
Newton made many contributions to astronomy. He defined the
laws of motion and universal gravitation which he used to
predict precisely the motions of stars, and the planets around
the sun. Using his discoveries in optics Newton constructed the
first reflecting telescope.
Sir Isaac Newton
Before Newton, science seemed a hodgepodge of
isolated facts and laws, capable of describing some
phenomena, but predicting only a few. Newton provided
science with a system of laws that can be applied to a
wide range of physical phenomena, and that can be used
to make exact predications. Newton published his works
in two books, namely "Opticks" and "Principia."
Newton’s laws
• Newton's First Law of Motion:
– Every object in a state of uniform motion tends
to remain in that state of motion unless an
external force is applied to it.
– Often termed simply the "Law of Inertia"
Wickedly Cool Example 1!
• Newton’s first law
– An object at rest…..
Wickedly Cool Example 2!
• Newton’s first law
– An object at rest…..
• tends to stay that way
Deep Thoughts On Physics
Deep Thoughts On Physics
• Interstellar Mission
– The mission objective of the Voyager Interstellar
Mission (VIM) is to extend the NASA exploration of
the solar system beyond the neighborhood of the outer
planets to the outer limits of the Sun's sphere of
influence, and possibly beyond.
Deep Thoughts On Physics
• At the start of the VIM, the two Voyager spacecraft had
been in flight for over 12 years having been launched in
August (Voyager 2) and September (Voyager 1), 1977.
Voyager 1 was at a distance of approximately 40 AU
(Astronomical Unit - mean distance of Earth from the Sun,
150 million kilometers) from the Sun, and Voyager 2 was
at a distance of approximately 31 AU.
Deep Thoughts On Physics
• Voyager 1 is now at the outer edge of our solar system, in
an area called the heliosheath, the zone where the sun's
influence wanes. This region is the outer layer of the
'bubble' surrounding the sun, and no one knows how big
this bubble actually is. Voyager 1 is literally venturing into
the great unknown and is approaching interstellar space.
Traveling at a speed of about one million miles per day,
Voyager 1 could cross into interstellar space within the
next 10 years.
Deep Thoughts On Physics
• Both Voyagers are headed towards the outer boundary of
the solar system in search of the heliopause, the region
where the Sun's influence wanes and the beginning of
interstellar space can be sensed. The heliopause has never
been reached by any spacecraft; the Voyagers may be the
first to pass through this region, which is thought to exist
somewhere from 8 to 14 billion miles from the Sun.
Deep Thoughts On Physics
•
Sometime in the next 5 years, the two spacecraft should
cross an area known as the termination shock. This is
where the million-mile-per-hour solar winds slows to about
250,000 miles per hour—the first indication that the wind
is nearing the heliopause. The Voyagers should cross the
heliopause 10 to 20 years after reaching the termination
shock
Deep Thoughts On Physics
• The Voyagers have enough electrical power and thruster
fuel to operate at least until 2020. By that time, Voyager 1
will be 12.4 billion miles (19.9 billion KM) from the Sun
and Voyager 2 will be 10.5 billion miles (16.9 billion KM)
away.
Deep Thoughts On Physics
•
Eventually, the Voyagers will pass other stars. In about
40,000 years, Voyager 1 will drift within 1.6 light years
(9.3 trillion miles) of AC+79 3888, a star in the
constellation of Camelopardalis. In some 296,000 years,
Voyager 2 will pass 4.3 light years (25 trillion miles) from
Sirius, the brightest star in the sky . The Voyagers are
destined—perhaps eternally—to wander the Milky Way
Deep thoughts….what if?..
• Both Voyager spacecrafts carry a greeting to any form of
life, should that be encountered. The message is carried by
a phonograph record - -a 12-inch gold-plated copper disk
containing sounds and images selected to portray the
diversity of life and culture on Earth. The contents of the
record were selected for NASA by a committee chaired by
Carl Sagan of Cornell University. Dr. Sagan and his
associates assembled 115 images and a variety of natural
sounds. To this they added musical selections from
different cultures and eras, and spoken greetings from
Earth-people in fifty-five languages.
Newton’s laws
• The Voyager spacecraft’s endless journey is
a great example of Newton’s first law of
motion. “An object in motion tends to stay
in motion.”
Newton’s laws
• Newton's Second Law of Motion:
– The relationship between an object's mass m,
its acceleration a, and the applied force F is
F = ma.
Acceleration and force are vectors. In this law
the direction of the force vector is the same as
the direction of the acceleration vector.
– Also called the “Law of Constant Acceleration”
Newton’s laws
• So, if
• Then,
F = ma…..
a = F/m
Newton’s laws
• Newton's Third Law of Motion:
– For every action there is an equal and opposite
reaction.
– Also called the “Law of Momentum”
So…what are the Forces?
• Strong force:
–
–
–
–
The force that holds atomic nuclei together.
The strongest of fundamental forces.
Has a very short range.
Usually attractive, but can sometimes be
repulsive.
So…what are the Forces?
• Electromagnetic force:
– Only acts between particles with electrical
charge.
– Holds atoms and molecules together.
– Has a nearly infinite range.
– Can be attractive or repulsive.
So…what are the Forces?
• Weak force:
– Is responsible for radioactive decay.
– Is much weaker than strong and
electromagnetic forces.
– Has a very short range.
So…what are the Forces?
• Gravity:
–
–
–
–
–
The force of attraction between two objects with mass.
The weakest of fundamental forces.
Has a nearly infinite range.
Always attractive, never repulsive.
Gravity’s magnitude depends on mass of and distance
between objects—the greater the distance, the smaller
the force.
– Earth’s gravity gives everything weight:
• Mass: amount of material in an object.
• Weight: force exerted on object’s mass by gravity.
So…what are the Forces?
• Friction:
– The force that slows down or stops the
movement of one object in contact with
another.
– Creates heat—the greater the friction, the
greater the heat.
– Friction experienced by objects traveling
through the air is called air resistance.
So…what are the Forces?
• Turning force:
– Results from two uneven forces independently
acting on an object (such as a push and pull).
– Causes an object to rotate around a fulcrum.
So…what are the Forces?
• Centripetal force:
– Causes an object traveling in a straight line to
follow a curved path.
– Usually creates circular motions that move
inward toward the center of rotation.