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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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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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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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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Physics Gened Jean