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Transcript of Physics Gened Jean
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PHYSICS
Licensure Examination for Teachers:
GENERAL EDUCATION
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VECTORS & SCALARS
Scalar quantitiesdescribed by magnitude,
e.g. 5 meters
Vector quantities
descibed both by magnitudeand direction, e.g. 5 metersNorth
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VECTORS SCALARS
DisplacementVelocity
Acceleration
Force, Momentum,Impulse, ElectricField, Magnetic Field
DistanceSpeed
Time, Temperature,Mass, Density,Electric Charge
Vector & Scalar Quantities
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Distance vs. Displacement
What is the displacement of an athletewho has run a lap on a 400-meter track?
Answer: Zero.
After running a lap, the athlete is back
where he or she started. The distancetraveled by the athlete, and not thedisplacement, is 400 meters.
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Speed vs. Velocity
As distance is to displacement, so speedis to velocity: the crucial differencebetween the two is that speed is a scalar
and velocity is a vector quantity.
A speedometer tells us the cars speed,
not its velocity, because it gives only a
number and not a direction. It does not tellus the average speed, but theinstantaneous speed, or the speed at a
given moment.
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Acceleration
Acceleration is a vector quantity thatmeasures the rate of change of thevelocity vector with time. Acceleration
happens when we speed up, slow down(deceleration), or change direction.
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Newtons Lawsof Motion
First Law: Inertia
Second Law: Acceleration
Third Law: Interaction
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LAW OF INERTIAA body remains atrest or moves in a straight line at a
constant speed unless acted upon by aforce.
INERTIA natural tendency of a body toresist changes in motion
First Law of Motion
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A soccer ball standing still on thegrass does not move until
someone kicks it. An ice hockeypuck will continue to move with thesame velocity until it hits the
boards, or someone else hits it.
First Law of Motion
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First Law of Motion
In free space where there is neither frictionnor air resistance to change the speed of amoving object, there is no force required to
maintain the object at a constant speed. It willcontinue moving in a straight line indefinitely.
When you push a glass with water initially at
rest, it begins to move, but the water has atendency to remain in its initial position. Ittends to get left behind and spills.
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First Law of Motion
Any change in the velocity of an object(non-uniform or accelerated motion) isevidence of a net force acting on that
object.
If you are in a moving car or bus that iscoming to a stop, your body tends to keep
moving forward. In a sudden stop, youtend to lurch forward.
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First Law of Motion
Mass is a measurement of a bodys
inertia, or its resistance to beingaccelerated.
Inertia of an object is proportional to itsmass: the greater the mass, the greaterthe inertia.
A piano is harder to push than a smallwooden chair because the piano is heavierand, therefore, has more inertia.
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Second Law of Motion
THE LAW OF ACCELERATION
Force = mass x acceleration
If the forces on an object are unbalanced, theresultant force will cause the object toaccelerate.
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Second Law of Motion
Acceleration is directly proportional to the netforce & inversely proportional to the mass.
The bigger the force and/or the smaller themass, the bigger the change in motion.
You accelerate by pushing harder on the sameobject, or by lightening the load while pushingwith the same force.
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Second Law of Motion
The forces are in the same direction and are,therefore, added producing a net or resultantforce of 25N to the right.
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Second Law of Motion
The box accelerates with a net force of 8N. Ifinitially the box is not moving, it will start tomove to the right. If it is already moving to the
right, it will move faster. If initially it is movingto the left, it will decelerate or move slower.
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Third Law of Motion
THE LAW OF INTERACTION
When an object exerts a force onanother object, the second object alsoexerts a force on the first object. Thesetwo forces act in opposite directions butare equal in magnitude.
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Third Law of Motion
Illustrations: When you push a book towards the left , the
book also exerts a force of equal magnitude onyour hand towards the right.
When a porter carries a heavy load on his head ,the load pushes down on his head. The porter'shead pushes the load upwards. Again, these
opposite forces are equal in magnitude. When you fire a gun, it thrusts the bullet out with
a great force. The bullet exerts the same forceon the gun, causing it to recoil.
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Third Law of Motion
When a stone is dropped, itfalls. This shows that the earthattracts the coin, i.e., it exertsa force on the coin in thedownward direction. Also, thecoin attracts the earth in theupward direction.
Air rushes out of a balloon,and the balloon streaks ahead.
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Third Law of Motion
Through its nozzle, a rocketspits gases (from burnt fuel)with tremendous speed; as aresult rocket is pushed up.
The birds, while flying, pushthe air downwards with thehelp of their wings, and the
air in turn exerts a force onthe bird in the upwarddirection.
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Third Law of Motion
When we walk on the ground, our foot pushesthe ground backward and the ground in turnexerts a force on the foot pushing the foot
forward. If you hit a wall with your fist, the wall also hits
your fist with the same force, which you feel.
If you slap someone on the cheek, his cheekalso 'hits' your hand with a force of equalmagnitude.
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Third Law of Motion
Points to remember:
Even though the action and reaction forcesare equal and opposite, their resultant is not
equal to zero as the action and reactionforces are acting on two different bodies
The third law holds good when the interacting
bodies are at rest or in motion This law does not give us the magnitude of
force
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Newtons Laws of Motion
The first law states that unbalanced forcesproduce a change in the velocity of the body.
The second law gives the exact amount of
force needed to produce a givenacceleration.
Newton's third law is a relation between the
forces themselves. When a body exerts aforce on another body, the other body alsoexerts a force of equal magnitude butopposite in direction on the first.
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Understanding Newtons Laws
While driving a car on the highway you hit abug. The bug hit the windshield and thewindshield hit the bug. Which of the twoforces is greater, the force on the bug or theforce on the windshield?
Answer: The same according to Newton's
third law you can only exert back as muchforce as is exerted on you. Because the bughas less mass, its motion is effected more bythe force.
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Understanding Newtons Laws
The resultant force is in the direction wherethe car is going. The bug changes velocity in
the reverse direction (decelerates)considerably. The car also decelerates,although this is hardly noticeable due to the
cars significantly larger mass compared tothe bugs.
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Mass vs. Weight
Mass measure of the quantity of matter,which is constant all over the universe.
Weight proportional to mass butdepends on location in the universe; forceexerted on a body by gravitationalattraction (usually by the earth).
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Law of Conservation of Energy
Energy can neitherbe created nordestroyed.
It is converted fromone form toanother.
The total energyalways remainsconstant.
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Law of Conservation of Energy
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Potential Energy
- Capacity to do work of objects at rest dueto their position or state
- A stone at the top of a hill, a strung arrow,an elongated rubber band, a wound clockor the wound spring of a toy car, waterstored in an over head tank, a tightly
coiled spring
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Kinetic Energy
- Capacity to do work of a moving body
- Blowing wind, water falling from heights, amoving vehicle
- For a moving object to do more work, itshould be moving faster
- If an object is moving, it also has momentum
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Momentum
Amount of motion in a body
Measure of how hard it is to stop a movingbody
Momentum = mass x velocity
Depends on how fast an object is movingand on its mass
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Work
Done by a force when it moves an objectthrough a distance in the direction in whichthe force is acting
Work = Force x Distance
No work is done even if force is applied toan object that does not move, e.g. pushinga concrete wall
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Archimedes Principle or
Law of Buoyancy When an object is wholly or partly immersedin a fluid, the fluid exerts an upward force onthe object. This force is equal to the weight ofthe fluid displaced by the object.
Principle behind the design of life savers,submarines, canoes, hot-air balloons
FLUID - any substance that tends to flow orfollow the shape of its container; liquids andgases
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Buoyancy: Hot-air Balloons
Hot air balloons rise into the air becausethe density of the air (warmer air) insidethe balloon is less than the density of the
air outside the balloon (cooler air). Theballoon and the basket displaces a fluidthat is heavier than the balloon and the
basket, so it has a buoyant force acting onthe system. Balloons tend to fly better inthe morning, when the surrounding air is
cool.
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Sound
Speed of sounddepends on theproperties of the
medium.
Travels markedly fast
in solids and liquids.
Cant travel in
vacuum.
These are the few examples of threshold decibels of noises made:
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Threshold Decibels
Threshold of hearing 0 dB Motorcycle (30 feet 88 dB
Rustling leaves 20 dB Food blender (3 feet) 90 dB
Quiet whisper (3 feet) 30 dB Subway (inside) 94 dB
Quiet home 40 dB Diesel truck (30 feet)
100
dB
Quiet street 50 dB Power mower (3 feet)107dB
Normal conversation 60 dB Pneumatic riveter (3 feet) 115 dB
Inside car 70 dB Chainsaw (3 feet) 117 dB
Loud singing (3 feet) 75 dBAmplified Rock and Roll (6feet)
120dB
Automobile (25 feet) 80 dB Jet plane (100 feet)130dB
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Radioactivity
The spontaneous emission of radiation ofparticles as a result of radioactive decay,or the disintegration of an unstable
nucleus
All elements heavier than lead, frombismuth (atomic number = 83), are
naturally radioactive
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Radioactive Decay
Alpha decay the nuclide splits out analpha particle, made up of two protons andtwo neutrons
Beta decay the nuclide emits betaparticles or electrons
Gamma decay an excited nuclide
releases its energy by emitting gammarays
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Radioactive Decay Series:
Uranium Uranium-238 naturally disintegrates in aseries of alpha and beta decays until it
becomes lead-206, which is stable1. Uranium-238 Thorium-234 + alpha
2. Thorium-234 Palladium-234 + beta minus
3. Palladium-234 Uranium-234 + beta minusOther radioactive decay series: thorium,neptunium, and actinium series
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Fusion Process in the Sun
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If a radio station were to increase its frequency from94.5 MHz to 99.1 MHz, what would happen to the
station's wavelength?
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The wavelength would go down.
As frequency increases, wavelengthdecreases, and vice versa.
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In the figure above, why are beta particles deflectedmore than alpha particles?
Beta particles are less massive than alpha particles.
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Radiation
The emissions from radioactive particles.
Gamma rays have no mass and carry noelectric charge.
The neutron to proton ratio determines thestability of an atom.
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Alpha and beta particles are alwaysassociated with the formation of newatoms. Gamma rays are massless forms
of energy that, on their own, do not lead tothe formation of new atoms.
Nuclear reactions change one element to
another, a process called transmutation.
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References
http://exploration.grc.nasa.gov/education/rocket/newton.html
http://www.gcsescience.com/pfm15.htm
Santisteban, C.J. 2007. Breaking ThroughPhysics. QC: C&E Publishing, Inc.
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