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The achiever’s guide to academic life and beyond…

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Science IV - 1 -

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PHYSICSPHYSICSPHYSICSPHYSICS
BASIC LAWS AND CONCEPTS

PHYSICSPHYSICSPHYSICSPHYSICS

- major science, dealing with the fundamental constituents of the universe, the forces they exert
on one another, and the results produced by these forces. Sometimes in modern physics a
more sophisticated approach is taken that incorporates elements of the three areas listed
above; it relates to the laws of symmetry and conservation, such as those pertaining to
energy, momentum, charge, and parity.

VECTORS AND SCALARSVECTORS AND SCALARSVECTORS AND SCALARSVECTORS AND SCALARS

Vectors and Net ForceVectors and Net ForceVectors and Net ForceVectors and Net Force

Often, an object will have many forces acting on it

simultaneously. Calculating the effect of each of the

forces separately can be extremely complex and difficult.

However, forces are vectors, and as such, any number of

forces can be combined into a single net force vector (R)

from which the object’s behavior can be determined.

ScalarScalarScalarScalar – a measure with magnitude but no direction.
(e.g., distance, mass, speed)

VectorsVectorsVectorsVectors – a measure with both magnitude and direction.
(e.g., force, acceleration, velocity)

MechanicsMechanicsMechanicsMechanics

Mechanics, branch of physics concerning the motions of objects and their response to forces. Modern
descriptions of such behavior begin with a careful definition of such quantities as displacement (distance
moved), time, velocity, acceleration, mass, and force. Until about 400 years ago, however, motion was
explained from a very different point of view. For example, following the ideas of Greek philosopher and
scientist Aristotle, scientists reasoned that a cannonball falls down because its natural position is in the
earth; the sun, the moon, and the stars travel in circles around the earth because it is the nature of
heavenly objects to travel in perfect circles.

The Italian physicist and astronomer Galileo brought together the ideas of other great thinkers of his
time and began to analyze motion in terms of distance traveled from some starting position and the

Page 2

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USTET, DLSUCET, PSHS-NCE, and other entrance tests.

Science IV - 2 -

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time that it took. He showed that the speed of falling objects increases steadily during the time of their
fall. This acceleration is the same for heavy objects as for light ones, provided air friction (air
resistance) is discounted. The English mathematician and physicist Sir Isaac Newton improved this
analysis by defining force and mass and relating these to acceleration. For objects traveling at speeds
close to the speed of light, Newton’s laws were superseded by Albert Einstein’s theory of relativity. For
atomic and subatomic particles, Newton’s laws were superseded by quantum theory. For everyday
phenomena, however, Newton’s three laws of motion remain the cornerstone of dynamics, which is the
study of what causes motion.

KineticsKineticsKineticsKinetics

Falling objects accelerate

in response to the force

exerted on them by

Earth’s gravity. Different

objects accelerate at the

same rate, regardless of

their mass. This

illustration shows the

speed at which a ball and

a cat would be moving and

the distance each would

have fallen at intervals of

a tenth of a second during

a short fall.

Kinetics is the description
of motion without regard
to what causes the
motion. Velocity (the time

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Science IV - 10 -

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Coulomb’s LawCoulomb’s LawCoulomb’s LawCoulomb’s Law

Objects with opposite charges attract each other, and objects with similar charges repel each other.
Coulomb’s law, formulated by French physicist Charles Augustin de Coulomb during the late 18th
century, quantifies the strength of the attraction or repulsion. This law states that the force between
two charged objects is directly proportional to the product of their charges and inversely proportional to
the square of the distance between them. The greater the charges on the objects, the larger the force
between them; the greater the distance between the objects, the lesser the force between them. The
unit of electric charge, also named after Coulomb, is equal to the combined charges of 6.24 × 1018
protons (or electrons).

EEEElectriclectriclectriclectric currentcurrentcurrentcurrent - is a movement of charge. When two objects with different charges touch and
redistribute their charges, an electric current flows from one object to the other until the charge is
distributed according to the capacitances of the objects. If two objects are connected by a material that
lets charge flow easily, such as a copper wire, then an electric current flows from one object to the
other through the wire. Electric current can be demonstrated by connecting a small light bulb to an
electric battery by two copper wires. When the connections are properly made, current flows through
the wires and the bulb, causing the bulb to glow. Electric current is measured in units called amperes
(amp). If 1 coulomb of charge flows past each point of a wire every second, the wire is carrying a
current of 1 amp.

ConductorsConductorsConductorsConductors are materials that allow an electric current to flow through them easily. Most metals are
good conductors.

IIIInsulatorsnsulatorsnsulatorsnsulators Substances that do not allow electric current to flow through them are. Rubber, glass, and air
are common insulators. Electricians wear rubber gloves so that electric current will not pass from
electrical equipment to their bodies.

VVVVoltage, oroltage, oroltage, oroltage, or PPPPotential otential otential otential DDDDifferenceifferenceifferenceifference

When the two terminals of a battery are connected by a conductor, an electric current flows through the
conductor. One terminal continuously sends electrons into the conductor, while the other continuously
receives electrons from it. The current flow is caused by the voltage, or potential difference, between
the terminals. The more willing the terminals are to give up and receive electrons, the higher the
voltage. Voltage is measured in units called volts. Another name for a voltage produced by a source of
electric current is electromotive force.

ResistanceResistanceResistanceResistance

A conductor allows an electric current to flow through it, but it does not permit the current to flow with
perfect freedom. Collisions between the electrons and the atoms of the conductor interfere with the flow
of electrons. This phenomenon is known as resistance. Resistance is measured in units called ohms. The
symbol for ohms is the Greek letter omega, Ω.

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Ohm’s LawOhm’s LawOhm’s LawOhm’s Law

The relationship between current, voltage, and resistance is given by Ohm’s law. This law states that
the amount of current passing through a conductor is directly proportional to the voltage across the
conductor and inversely proportional to the resistance of the conductor. Ohm’s law can be expressed as
an equation, V = IR, where V is the difference in volts between two locations (called the potential
difference), I is the amount of current in amperes that is flowing between these two points, and R is the
resistance in ohms of the conductor between the two locations of interest. V = IR can also be written R
= V/I and I = V/R. If any two of the quantities are known, the third can be calculated. For example, if a
potential difference of 110 volts sends a 10-amp current through a conductor, then the resistance of the
conductor is R = V/I = 110/10 = 11 ohms. If V = 110 and R = 11, then I = V/R = 110/11 = 10 amp.

ELECTRIC CIRCUITSELECTRIC CIRCUITSELECTRIC CIRCUITSELECTRIC CIRCUITS

An electric circuit is an arrangement of electric current sources and conducting paths through which a
current can continuously flow. There are two basic ways in which the parts of a circuit are arranged.
One arrangement is called a series circuit, and the other is called a parallel circuit.

Series CircuitsSeries CircuitsSeries CircuitsSeries Circuits

If various objects are arranged to form a single conducting path between the terminals of a source of
electric current, the objects are said to be connected in series. The electron current first passes from the
negative terminal of the source into the first object, then flows through the other objects one after
another, and finally returns to the positive terminal of the source. The current is the same throughout
the circuit. In the example of the light bulb, the wires, bulb, switch, and fuse are connected in series.

Parallel CircuitsParallel CircuitsParallel CircuitsParallel Circuits

If various objects are connected to form separate paths between the terminals of a source of electric
current, they are said to be connected in parallel. Each separate path is called a branch of the circuit.
Current from the source splits up and enters the various branches. After flowing through the separate
branches, the current merges again before reentering the current source.

MAGNETISMMAGNETISMMAGNETISMMAGNETISM

Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature. Magnetic forces
are produced by the motion of charged particles such as electrons, indicating the close relationship
between electricity and magnetism. The unifying frame for these two forces is called electromagnetic
theory (see Electromagnetic Radiation). The most familiar evidence of magnetism is the attractive or
repulsive force observed to act between magnetic materials such as iron. More subtle effects of
magnetism, however, are found in all matter. In recent times these effects have provided important
clues to the atomic structure of matter.

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Science IV - 19 -

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the differences in quality, or timbre. The ear perceives distinctly different qualities in the same note
when it is produced by a tuning fork, a violin, and a piano.

Speed of Sound Speed of Sound Speed of Sound Speed of Sound

The speed of sound in dry, sea level air at a temperature of 0°C (32°F) is 332 m/sec (1,088 ft/sec). The
speed of sound in air varies under different conditions. If the temperature is increased, for example, the
speed of sound increases; thus, at 20°C (68°F), the speed of sound is 344 m/sec (1,129 ft/sec). The
speed of sound is different in other gases of greater or lesser density than air. The molecules of some
gases, such as carbon dioxide, are heavier and move less readily than molecules of air. Sound
progresses through such gases more slowly.

Decibel ScaleDecibel ScaleDecibel ScaleDecibel Scale
The decibel scale is used primarily to compare sound intensities although it can be used to compare
voltages.

Decibels Typical sound

0 threshold of hearing

10 rustle of leaves in gentle breeze

10 quiet whisper

20 average whisper

20-50 quiet conversation

40-45 hotel; theater (between performances)

50-65 loud conversation

65-70 traffic on busy street

65-90 Train

75-80 factory (light/medium work)

90 heavy traffic

90-100 Thunder

110-140 jet aircraft at takeoff

130 threshold of pain

140-190 space rocket at takeoff

NUCLEAR PHYSICSNUCLEAR PHYSICSNUCLEAR PHYSICSNUCLEAR PHYSICS

NuclearNuclearNuclearNuclear F F F Fusionusionusionusion

The release of nuclear energy can occur at the low end of the binding energy curve (see accompanying
chart) through the fusion of two light nuclei into a heavier one. The energy radiated by stars, including
the Sun, arises from such fusion reactions deep in their interiors. At the enormous pressure and at

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temperatures above 15 million ° C (27 million ° F) existing there, hydrogen nuclei combine according to
equation (1) and give rise to most of the energy released by the Sun.

Fission and FusionFission and FusionFission and FusionFission and Fusion

Nuclear energy can be released in two different ways: fission, the splitting of a large nucleus, and

fusion, the combining of two small nuclei. In both cases energy—measured in millions of electron volts

(MeV)—is released because the products are more stable (have a higher binding energy) than the

reactants. Fusion reactions are difficult to maintain because the nuclei repel each other, but fusion

creates much less radioactive waste than does fission.