"Definition of PHYSICS "
Science is built up with facts
as a house is with stones.
But a collection of facts
is no more a science
than a heap of stones
is a house.
as a house is with stones.
But a collection of facts
is no more a science
than a heap of stones
is a house.
Jules Henri Poincaré 1903
la Science et l'Hypotheses
la Science et l'Hypotheses
Physics is the study of the interactions between physical systems. The physicist attempts to describe the interaction with the most fundamental and general law or principle possible. As an example James Clerk Maxwell summarized all of classical electromagnetic theory into four simple equations; Maxwell's Equations. With these relations one can understand such diverse phenomena as electric power generation, the refrigerator magnet that holds up your shopping list, the bonding of chemical elements, and why a balloon will stick to the ceiling after it has been rubbed on your sweater. Nature is complex and beautiful. To the physicist this beauty is enriched when we perceive the underlying simplicity of physical laws. Achieving this understanding is very difficult in the face of the complex interactions that take place around us each day. The physicist begins with the simplest systems that she or he can identify. The history of Maxwell's insight illustrates how the physics community works from simple isolated systems toward a fundamental and general law (or set of laws).
All electrical phenomena involve the interaction between positive and negative charges. The earliest studies began by isolating positive and negative objects and observing their interactions. Charles Augustin de Coulomb (and others) performed these experiments. His results were rewritten in a particularly powerful form by the great mathematician Karl Friedrich Gauss. Hans Christian Oersted was the first to report a connection between magnetism and electricity when he noticed that a wire carrying an electric current disturbed the needle of a nearby compass. André Marie Ampére and others described how electric currents can create magnetic effects and Michael Faraday showed that changing magnetic phenomena creates electrical phenomena. This increasingly complex understanding was built at each step on relatively simple experiments or observations. With the addition of a single term to Ampére's Law, Maxwell recognized that all classical electromagnetic effects were described by the four equations he compiled.
Sir Isaac Newton is often mentioned as the person who made the greatest contribution to physics. It is easy to understand why he receives this distinction. Newton was the first to describe a fundamental force of nature mathematically. Not satisfied that his arguments were sound, Newton invented the calculus to help calculate the gravitational force of the Earth on the Moon.Being the first to find a truly fundamental and universal law of nature would have insured his reputation. However Newton's contribution was deeper than this. The basic relationship between causes (forces) and effects (motion) was not established in Newton's time. More than four thousand years of debate among natural philosophers had not resolved this fundamental issue. Newton demonstrated that force produces acceleration (not velocity!). In his famous Principia Mathematica Newton solved the problem of the Moon's motion around the Earth. His reasoning extended from the fundamental force law all the way to the resulting motion, with both crucial links devised by him. This was a compelling achievement. More than this, it established a model for all physicists to follow.
These two pieces of the history of physics serve well to illustrate the spirit and essence of physics. Some part of the physical world draws our attention. As we seek to understand it we must first tease away the distracting elements. If we succeed by stages to reach a truly fundamental understanding, all of the secrets of the original complex phenomena should become clear to us. Of course science, like life, is rarely this easy. The process of discovery is ongoing. To appreciate the central problem of physics today one final piece of history sets the stage.
In 1949 Richard Feynman put the finishing touches on Quantum Electro-Dynamics (QED). In one theory Feynman had united Quantum Mechanics, Relativity, and Electromagnetism (viewed as a single force since Maxwell's time). QED is the single most accurate predictor that science has devised and in one step it has removed electromagnetics as a research field in physics because it is now completely understood (at least in principle).
By the middle of this century physics had discovered that four fundamental forces were responsible for all of the interactions in nature that we could perceive. These were the Strong and the Weak nuclear forces, the Electromagnetic force (now described by QED), and Newton's gravitational force. Between 1966 and 1968 Stevan Weinberg and Abdus Salam brought the Weak Nuclear force and the Electromagnetic Force together and described them as a single type of interaction (called the Electroweak force).This great success in unifying separate fundamental interactions in a single theory established the theme for modern physics.
The physics community took the hint. Electricity and Magnetism are one phenomena not two. Then, the Electromagnetic Force and the Weak nuclear force are one phenomena not two. Why stop there? Is it not possible that all of the four forces were really different aspects of a single fundamental force?
The answer is that we are stuck. Many clever proposals have been made since QED was published. In each case our understanding of some phenomena has improved. But each theory has proved unsatisfactory in some way. The search has produced the theory of the Big Bang, Lasers, the transistor, computers, and the World Wide Web. All are direct products of QED and the subsequent search for a Unified Field Theory. We're still working on it.
Sticking to the central theme brings us to the end of the story quickly, but of course many interesting and exciting parts get left out. Finding the underlying law is like finding the architects plan for the house. Having natures plan helps us devise tools to increase our understanding. But having the plans and the tools will not by itself build the house. You must also gather the stones.
Considerable research took place between Maxwell's publication and the invention of radio. With radio reception we are able to gather data about stars and galaxies that were invisible before. Pulsars (rapidly spinning nutron stars) were discovered in 1968 by Jocelyn Bell Burnell. Another part of the electromagnetic spectrum, X-Rays, gives us the signature of black holes. But X-Rays can also let us look into the human body or determine the structure of crystals. The structure of DNA was deduced by Rosalind Franklin from a crystallized sample in just this way. As another example, we understand the Strong Nuclear Force, but the detailed structure of the nucleus is still an active research area. And one of the early experimental tools in this research was Nuclear Magnetic Resonance. This phenomena, exhibited by all atoms, is at the heart of every Magnetic Resonance Imaging (MRI) exam in our hospitals. Because of its ability to show soft tissue structure MRI has been a powerful tool in biological research.Even building the mathematical tools has led to remarkable technologies. An early difficult mathematical problem in the field of Nuclear and Particle Physics was the Inverse Scattering Problem. The Inverse Scattering Problem is to deduce the structure of any object (in this case the nucleus) by reconstructing the history of scattered waves.The solution of this famous problem led directly to the development of devices used for oil exploration and earthquake prediction by deducing the geologic structure of the earth. This technology is also built into the computer that analyzes every diagnostic ultrasound exam.
The field of physics lies behind all of our technology. No brief summary could do justice to the topic. As you study physics do not become too distracted by the pretty stones you find. (Also do not become discouraged if you trip over a few.) Remember you want to see the entire house.
CHAPTER 1 : INTRODUCTION TO PHYSICS
1.1 : Understanding physics -- natural phenomena in daily life
-- field of study in physics
1.2 : Base quantities and derived quantities -- 5 base quantities
-- derived quantities
-- prefixes and scientific notation
( standard form )
1.3 : Scalar and vector quantities -- scalar quantities
-- vector quantities
1..4 : Measurements -- errors in measurement
-- consistency , accuracy , and sensitivity
-- measurement instruments
1.5 : Scientific investigations -- making inference
-- formulating a hypothesis
-- controlling variables
-- list of apparatus and materials
-- procedure of experiment
-- tabulation of data
-- analysis of data
1.1 understanding physics
1. Physics
The branch of science concerned with the study of natural phenomena and properties
of matter and energy .
2. A phenomenon
An occurrence that can be perceived by our senses .
3. Fields of study in physics :
(a) introduction to physics
(b) forces and motion
(c) forces and pressure
(d) heat
(e) light
(f) waves
(g) electricity
(h) electromagnetism
(i) electronics
(j) radioactivity
4. Importance of physics
(a) There is a close relationship between the study of physics and other sciences ,
including astronomy , biology , chemistry and geology .
(b) There is a close connection between physics and the practical developments in
engineering , medicine and technology .
(c) The application of fundamental laws and theories have enabled engineers and
scientists to put satellites into orbit , receive information from space probes ,
and improve telecommunications .
(d) Research in physics has led to the use of radioactive materials in the study ,
diagnosis , and treatment of certain diseases.
(e) Physics improves the quality of life , i.e many home appliances function through
The operation of principles of physics .
1.2 Base Quantities and Derived Quantities
1. A physical quantity
A quantity that can be measured .
2. Every physical quantity is expressed as a numerical value in a particular unit of
measurement . For example .
Length of a meter rule = 100 cm
Physical quantity numerical value unit of measurement
3. A unit
A quantity adopted as the standard by which any other quantity of the same kind is
measured .
4. Base quantity
Physical quantity that cannot be defined in terms of other physical quantity
5. Table below shows five base quantities and their respective SI units .
Base quantities | S. I . units | ||
Name | Symbol | Name | Symbol |
Length | l | meter | m |
Mass | M | kilogram | kg |
Time | T | second | s |
Temperature | T | Kelvin | K |
Electric current | I | Ampere | A |
6. Derived quantities
Physical quantities derived from base quantities by multiplication or division or both
Derived quantities | Formula | Derived units | |
Name | Symbol | Units | |
Area | A | Length x breadth | m x m = m 2 |
Volume | V | Length x breath x height | m x m x m = m 3 |
velocity | v | Displacement / time taken | m / s = m s -1 |
Acceleration | a | Change in velocity / time | m s -1 / s = m s -2 |
Momentum | mom. | Mass x velocity | kg m s -1 |
Density | ρ | Mass / volume | kg m -3 |
Force | F | Mass x acceleration | kg m s-2 // |
Pressure | P | Force / surface area | N m -2 // Pascal , Pa |
Work | W | Force x displacement | Nm // Joule , J |
Power | P | Work / time taken | J s -1 // watt , w |
7. Scientific notation ( standard form )
(a) a shorter method of expressing very large or very small numbers .
(b) is based on powers of the base number 10 .
(c) in standard form is written as : - A x 10 n
where 1 < A < 10 , and n is an integer .
8. Prefixes
(a) is a group of letters placed at the beginning of a word to modify its meaning .
(b) acts as multipliers
(c) for easier recording and comparison of very large or very small measurements of
physical quantities .
Prefix | Power / factor | Symbol | Example | Symbol |
Tera | x 10 12 | T | Tetrameter | Tm |
Giga | x 10 9 | G | Gigagram | Gg |
Mega | x 10 6 | M | megawatt | MW |
Kilo | x 10 3 | k | kilojoule | kJ |
hecto | x 10 2 | h | hectometer | hm |
deca | x 10 1 | da | decasecond | das |
deci | x 10 -1 | d | decimeter | dm |
centi | x 10 -2 | c | centimeter | cm |
milli | x 10 -3 | m | milliampere | mA |
micro | x 10 -6 | μ | microsecond | μs |
nano | x 10 -9 | n | nanometer | nm |
pico | x 10 -12 | p | picometer | pm |
1.3 Scalar and Vector quantities
1. A scalar quantity
Is a physical quantity which has magnitude only .
2. A vector quantity
Is a physical quantity which has both magnitude and direction .
3. Table shows examples of scalar quantities and vector quantities.
Scalar quantities | Vector quantities |
distance | displacement |
speed | velocity |
mass | weight |
energy | momentum |
time | impulse |
electric current | acceleration |
power | deceleration |
density | force |
1.4 Measurements
A : Measurement
1. Measurements
Trials to determine the value of a particular physical quantity .
2. Error
The difference between the true value of a quantity and the value obtained in
measurement .
3. There are two main types of errors
(a) systematic errors
(b) random errors
4. Systematic errors
-- are cumulative errors that can be compensated for , if the errors are known.
-- result from (i) an incorrect position of the zero point or zero error .
(ii) an incorrect calibration of the measuring instrument .
-- can be eliminated or corrected if the measuring instruments are calibrated of
adjusted frequently .
5. Random errors
-- arise from unknown and unpredictable variations in condition , and will produce a
different error every time you repeat the experiment .
-- may be due to
(a) personal error ( human limitations of sight and touch )
(b) lack of sensitivity ( instrument does not respond / indicate insignificant or
small change )
(c) natural errors ( wind , temperature , humidity , refraction , magnetic field or
gravity )
(d) wrong technique ( applying excessive pressure when turning a micrometer
screw gauge )
-- can be minimized by repeating the measurement several times and taking the
average or mean value of the reading .
6. Parallax error
An error in reading an instrument because an observer’s eye and the pointer are not
in a line perpendicular to the plane of the scale .
B : Consistency , Accuracy , and Sensitivity
Consistency // Precision
1. The ability to record the same / consistent readings when a measurement is repeated .
2. A measurement is considered consistent will have a small relative deviation or no
deviation from the mean / average value .
3.. A deviation
The difference between a measurement value and its mean value or average value .
Deviation
4. average deviation = ---------------------------
No. of values taken
average deviation
5. relative deviation = ------------------------------- x 100 %
average value
6. Consistency can be improved by
(a) eliminating parallax errors
(b) exercising greater care and effort when taking readings.
(c) using an instrument which is not defective .
Accuracy
1. the degree of a measuring instruments to record close to / almost equal to the actual
value .
2. The level of accuracy is related to the relative error .
error
3. relative error = ----------------------- x 100 %
actual value
4. An error
The difference between the measured value and the actual value or true value .
5. Accuracy can be improved by : -
(a) repeated readings are taken and the average value is calculated
(b) avoid parallax errors
(c) avoid zero errors
(d) use measuring instruments with a higher accuracy . For example , a vernier
caliper is more accurate than a ruler .
Comparisons between Consistency and Accuracy
Sensitivity
1. The ability to detect quickly a small change in the value of a measurement .
2. A measuring instrument that has a scale with a smaller divisions is more sensitive .
Measuring instruments.
A : Measurement of length
Measuring instruments | Accuracy / sensitivity |
Ruler | 0.1 cm |
Vernier caliper | 0.01 cm |
Micrometer screw gauge | 0.001 cm |
1. Ruler
To measure length from a few cm up to 1 m
2. Precations to be taken when using a ruler :
(a) ensure that the object is in contact with the ruler to avoid inaccurate readings.
(b) avoid parallax errors
(c) avoid zero and end errors .
3. For example : A ruler is to determine the diameter of the wire ?
Solution :
Length of wire
Diameter of wire , d = ----------------------------
No. of coils
1.5 - 1.0
= -------------------
10
= 0.05 cm
Vernier caliper
1. Two pairs of jaws
(a) outside jaws : to measure linear dimensions and outer diameters
(b) inside jaws : to measure inner diameters
2. Two steel bar scales
(a) the main scale
(b) the vernier scale -- has a scale on which ten divisions are equal to nine small
divisions on the main scale .
3. Errors in the vernier caliper
(a) No zero error
(b) Positive zero error (c) Negative zero error
Positive zero error = + 0.04 cm Negative zero error = - ( 0.1 - 0.08 )
= - 0.02 cm
4. For example : Figure below shows the use of a vernier caliper to measure the size of
spherical object . Determine the correct size of the object if the zero
error of the vernier caliper is (a) - 0.08 cm ; (b) + 0.08 cm .
(a) Zero error = - 0.08 cm
Main scale reading = 2.10 cm
Vernier scale reading = 0.05 cm
Vernier caliper reading = 2 . 1 + 0.05 = 2.15 cm
Correct size of object = vernier caliper reading - zero reading
= 2.15 - ( -0.08 ) = 2. 23 cm
(b) Correct size of object = 2.15 - ( +0.08 ) = 2. 07 cm
Micrometer Screw Gauge
1. comprises of (a) main scale on the sleeve
(b) thimble scale on the thimble
2. Errors in micrometer screw gauge
(a) No zero error
(b) Positive zero error (c) Negative zero error
Correct reading Correct reading
= micrometer reading - ( 0.04 ) = micrometer - ( -0.03 )
3. For example :
Figure above shows a micrometer screw gauge used to measure the size of an object.
Determine the size of the object if the micrometer has a zero error of (a) + 0.01 mm
; (b) - 0.03 mm
Solution :
The main scale reading = 4.50 mm
The thimble scale reading = 0.21 mm
The reading of the gauge = 4.50 + 0.21 = 4.71 mm
(a) Size of object = the reading of the gauge - zero error
= 4.71 - 0.01
= 4.70 mm
(b) Size of object = 4.71 - ( - 0.03 )
= 4.74 mm
B : Measurement of time
1. Stop watches are used to measure time interval .
2. Two types of stop watches
(a) The analogue stop watch which is mechanically operated
(b) The digital stop watch which is electronically operated.
C : Measurement of mass
1. The mass of an object can be measured using a beam balance or an electronic balance .
D : Measurement of temperature
1. A thermometer is an instrument used to measure temperature
2. Types of thermometer
(a) clinical thermometer
(b) mercury thermometer ( range – 10 0 C to 110 0 C with an accuracy of 1 0 C )
(c) mercury thermometer ( range 0 0 C to 360 0 C with an accuracy of 2 0 C )
3. A mercury thermometer is a sensitive instrument because : -
(a) Mercury is a liquid metal which is sensitive to temperature changes. It expands
And contracts uniformly with the temperature .
(b) The thin – walled glass bulb allows a quick heat transfer between the heat
source and the mercury
(c) The capillary tube , which has a small diameter , amplifies a small expansion
in the bulb into a large linear expansion along the length of the capillary tube .
E : Measurement of electric current and voltage
Ammeter
1. An instrument used to measure the amount of electric current flowing through a
particular point in an electrical circuit .
2. The SI unit for current is Ampere , A
3. For a small current , a milliammeter is used ( an accuracy of 0.1 m A or 0.2 mA is used )
4. It is usually connected in series in an electrical circuit .
Voltmeter
1. An instrument used to measure the potential difference ( voltage ) between any two
points in an electrical circuit
2. The SI unit for potential difference is volt / V.
3. It is connected in parallel in an electrical circuit .
1.5 Scientific Investigations
1. The steps for a systematic scientic investigation.
Steps 1 : Making an observation
2 : Drawing an inference
3. : Identifying and controlling variables -- manipulated variable
-- responding variable
-- constant variable
4 : Formulating a hypothesis
5 : Conducting the experiment -- aim
-- apparatus and material
-- procedure
-- tabulating data
-- drawing graph
-- analysis data
2. The steps for a laboratory report .
Steps 1 : inference
2 : hypothesis
3 : aim
4 : variables --manipulated variable , responding variable , constant variable
5 : apparatus and materials
6. : arrangement of apparatus
7 : experiment procedures -- the method for controlling manipulated variable -- the method for measuring responding variable
8 : tabulation of data
9 : graph to show relationship between manipulated and responding variable
CHAPTER 2 : FORCE AND MOTION
2.1 : Linear motion -- distance and displacement ; speed and velocity
-- acceleration and deceleration ; linear motion
2.2 : Motion graphs -- displacement – time graphs ; velocity - time graphs
-- acceleration – time graphs
2.3 : Inertia : -- concept of inertia ; relationship between inertia and mass
-- Newton
2.4 : Momentum and Conservation of momentum : -- concept of linear momentum
-- collisions and explosion
-- principle of conservation of momentum
2.5 : The effect of a force -- force , F = m a ; balanced and unbalanced forces
-- Newton
2.6 : Impulse and Impulsive Force -- change in momentum ; impulsive forces
-- benefits of impulsive force ; ways of reducing impulsive forces
2.7 : Safety Features in the Vehicles -- safety features in vehicles and its importance
2.8 : Gravity : -- gravitational force ; gravitational field strength
-- gravitational acceleration , g ; weight , W = m g
2.9 : Forces in Equilibrium -- zero resultant forces ; principle of resultant forces
-- Newton
2.10 : Work , Energy , Power and Efficiency -- work , W = F s
-- kinetic energy ; potential energy , Power
2.11 : The Importance of maximizing the Efficiency of Devices
-- appreciating the importance of maximizing efficiency
-- maximizing of efficiency of devices
2.12 : Elasticity -- intermolecular force
-- Hooke ‘s Law
2.1 Linear motion
1. Kinematics
The study of motion of objects without involving the forces acting on the object .
2. Dynamics
The study of motion of objects with the forces acting on the object .
3. Linear motion
Motion in a straight line
4. Distance , s
Total distance of the path traveled by an object .
-- scalar quantity .
-- S .I unit is metre / m
5. Displacement , s
The distance of its final position from its initial position in a specific direction .
-- vector quantity
-- S. I unit is metre / m
6. Speed , u , v
The rate of change of distance
Distance traveled
Speed = ---------------------------
Time taken
-- S. I unit is m s -1
-- scalar quantity
7. Velocity , u , v
The rate of change of displacement .
Displacement
Velocity = ----------------------
Time taken
-- S.I unit is m s -1
-- vector quantity
8. Uniform speed
Speed that remains the same in magnitude regardless of its direction
9. Uniform velocity
Velocity that remains the same in magnitude and direction.
10 . A non – uniform velocity :-
(a) the direction of motion changes or the motion is not linear
(b) the magnitude of velocity changes
11. Acceleration , a
The rate of change of velocity
Change in velocity
Acceleration = -------------------------------
Time taken
Final velocity - initial velocity
= ------------------------------------------
Time taken
v - u
a = -------------
t
-- vector quantity
-- S. I unit is m s -2
-- positive acceleration // + a
12. Deceleration , - a
The velocity of an object decreases from an initial velocity , u to a lower final
velocity , v ( u > v )
-- negative acceleration
13. Acceleration is zero
An object is moving at a constant velocity i.e , the magnitude and direction of the
velocity remain unchanged .
Note :
14. An object is moving with a decreasing acceleration , is not necessary experiencing a
deceleration .
15. Example 1 : A boy is moving 100 m to the East , then 100 m to the North and at the
end 100 m to the West . What is the total distance travelled by the boy
and the displacement from the starting point ?
