LESSON 1
Physics is a major science, dealing with the systematic study of the basic properties of the universe, the forces they exert on one another, and the results produced by these forces. It is the remaining core of naturl philosophy and concerns itself with questions of what underlies the interactions of matter, energy, space and time, and even with what constitutes reality. It is not surprising that a field that has produced the theories of relativity and quantum mechanics and has drastically altered our concept of the universe has an aura of mystery --- of being remote from everyday experience and impossible to understand. Once one becomes accustomed to looking for an explanation of various phenomena in terms of underlying scientific principles, it is possible to see physics everywhere. The flight of birds, the operation of a microwave oven, the color of the sunset, and the pitch of one’s voice all have basic explanations in physics. Those explanations can be understood by anyone, not just professional scientists.
Physics is closely related to the other natural sciences and, in a sense, encompasses them. Chemistry, for example deals with the interaction of atoms to form molecules. Much of modern geology is largely a study of the physics of the earth and is known as geophysics. Astronomy deals with the physics of the stars and outer space. Even living systems are made up of fundamental particles and, as studied inbiophysics and biochemistry, they follow the same type of laws as the simpler particles traditionally studied by a physicist.
The emphasis on the interaction between particles in modern physics, known as the microscopic approach, must often be supplemented by a macroscopic approach that deals with larger elements or systems of particles. This macroscopic approach is indispensable to the application of physics to much of modern technology.Thermodynamics, a branch of physics developed in the 19th century, deals with the elucidation and measurement of properties of a system as a whole and remains useful in other fields of physics; it also forms the basis of much of chemical and mechanical engineering. Such properties as the temperature, pressure and volume of a gas have no meaning for an individual atom or molecule; these thermodynamic concepts can only be applied directly to a very large system of such particles. A bridge exists, however, between the microscopic and macroscopic approach; another branch of physics; known as statistical mechanics, indicates how pressure and temperature can be related to the motion of atoms and molecules on a statistical basis.
Physics emerged as a separate science only in the early 19th century, until that time a physicist was often also a mathematician, philosopher, chemist, biologist, engineer, or even primarily a political leader or an artist. Today, the field has grown to such an extent that with few exceptions modern physicists have to limit their attention to one or two branches of the science. Once the fundamental aspects of a new field are discovered and understood, they become the domain of engineers and other applied scientist. The 19th century discoveries in electricity and magnetism, for example, are now the concentrations of electrical and communication engineers; the properties of matter discovered at the beginning of the 20th century have been applied in electronics; and the discoveries of nuclear physics, have passed into the hands of nuclear engineers for applications to peaceful or military uses.
MATHEMATICS as a language of science
Mathematics is the language of physics; that is when ideas in science are expressed in mathematical terms:
1. They are unambiguous.
2. They do not have double meanings, that so often confuse the discussion of ideas expressed in
common language.
3. They are easier to verify or disprove by experiment.
4. The methods of mathematics and experimentation led to enormous success in science.
5. The abstract mathematics developed by mathematicians is often years later found to be the
exact language by which nature can be described.
Mathematics is the language of physics does not mean that mathematics is physics or physics is mathematics.
THE SCIENTIFIC METHOD – is a method that is extremely effective in gaining, organizing, and applying new knowledge. The steps are :
1. Recognize a problem.
2. Make an educated guess --- a hypothesis. Hypothesis is an educate guess that is only considered factual after it has been demonstrated by experiments. If a hypothesis has been tested over and over again and has not been contradicted it may become known as a law or principle.
3. Predict the consequences of the hypothesis
4. Perform experiments to test predictions.
5. Formulate the simplest general rule that organizes the three main ingredients --- hypothesis, prediction, and experimental outcome --- into a theory.
The success of science has more to do with an attitude common to scientists than with a particular method. This attitude is one of inquiry, observation, experimentation and humility.
PHYSICS IN THE HEALTH SCIENCES
Physics, whether one is aware of it or not, is encountered in many situations --- recreational, occupational, and even social. The situations described in this section are but a few, of the many, particularly in the health sciences.
* Athletics. We do not all have an intuitive feeling for how to use our bodies most effectively. Even the great athletes learn from their coaches. One important area of study in modern athletics is kinesiology, literally the study of motion. It is based on the relationships between distance, time, velocity, and acceleration, as well as the
concepts of force, work, energy, and power. Studying these chapters will allow a deeper understanding of the body, its muscles, and its utilization of energy in terms of underlying physics that may already been familiar. As an illustration, one knows that it is harder to carry an object at arm’s length than close to the body. Experience makes it obvious, but physics tells us why. ( It has to do with where the muscles are attached to bones in relation to the joints).
* Traction systems. Some traction systems seem to have wires, pulleys, and weights going every which way and performing altogether mysterious tasks. The traction system will show the importance of not only the strength of a force, but also the direction of the force and the point where it is applied. The strength of the force in traction will obviously depend on how large a weight is used. The direction of the force will be the same as the direction of the wire attached to the subject. The point of application is the place where the wire is attached. The analysis if the traction system is by using Newton’s laws.
* Nutrition and Exercise. Few things have caught the attention of the public as have nutrition and exercise over the last several years. It turns out that work is the manifestation of energy changing forms. In humans, work changes stored food energy into heat, motion and other forms of energy. When work, energy, power, and efficiency are studied, they will be related to food energy and human exercise. Energy is one of the central concepts of physics.
* Body Temperature. Humans and other warm-blooded animals maintain a constant body temperature by converting food energy to heat energy. However, the body continues to produce heat even when surrounding temperature are higher than the body temperature. That excess heat is dissipated by perspiring. Various methods of heat transfer are presented, and it will become clear why perspiration is the body’s only possible method of dissipating heat when surrounding temperatures are high. It will also be seen why an alcohol rub reduces body temperature, as might be necessary with a high fever. The concept of efficiency makes it evident that the body te body creates even more heat than normal during exercise since a large fraction of the food energy used in producing muscle contractions ends up s heat instead. As a consequence, the body requires more cooling and perspires more during exercise than when at rest.
* Physical Therapy. Patients undergoing physical therapy usually have weakened or damaged muscles or suffer from nerve disorders that make it difficult for them to move their muscles effectively. A great deal of physical therapy takes place in water because the water helps to support the weight of the person. Being in water greatly reduces the effective weight of the person and of his limbs, making it possible for him to perform exercises that would be impossible out of the water. The underlying physical principle is called Archimedes’ principle and the physics of fluids.
* Blood Flow and Respiration. Liquids and gases can be made to move by application of pressure. Pressure and methods of transmitting and measuring pressure are in the later chapters. The flow of liquids and gases in general as well as in biological systems will also be studied in depth. For example, the heart creates blood pressure by exerting force on the blood with a muscular contraction. The subsequent blood flow is regulated by blood vessels changing diameter and thereby changing their resistance to flow. Other examples of the body’s use of pressure include breathing, maintenance of reduced pressure in the chest cavity to keep the lungs from collapsing, and pressure in the eye to maintain its shape.
* Hearing. Hearing is the perception of sound. Sound is the first example of a wave phenomenon. Hearing and sound will be studied in chapter 8 and 9, where it will be shown how hearing does not simply reproduce the actual physical properties of sound. For example, loudness is the perceived intensity of sound waves. However, humans do not perceived ultrasound at all, so loudness is not a perfect indication of intensity and hence differs from that physical characteristics.
* Ultrasonic Scanners. Ultrasound is any sound that is so high pitched that the average person can’t hear it. Ultrasound still behaves in a fashion similar to audible sound waves. For example, it scatters from boundaries between substances and so can be used to probe the inside of the body noninvasively, much as submarines use sonar to view objects in dark waters. Ultrasonic waves can be made perfectly safe by keeping their intensity low enough. If this is done, the ultrasound can not cause injury because it lacks energy to do so. Ultrasonic scanners are compared with other tools for probing the interior of the body, such as x-rays.
* Electrical Safety. Certain medical procedures make hospital patients extremely sensitive to electric shock. The reasons for the sensitivity will be explained in chapter 12 and some of the major methods of protection will be presented. This include the three-wire-system, proper grounding of appliances and the use of circuit breakers. As usual, the study of electrical safety will be based on the principles of physics ( learned from the study of electricity and magnetism in chapter 10 and simple electric circuits in chapter 11).
* Nervous System. The nervous system is a complex of biological electric circuits that controls the muscles, among others things. Chapter 13 is entirely devoted to bioelectricity. In this chapter it will be seen that bioelectricity can be recorded and interpreted to yield great deal of information on the functioning of certain body organs. The most common such recording is the electrocardiogram, literally recording of the electrical impulses that control the beating of the heart. Electrocardiograms give detailed information about the condition of that organ. Similarly, information can be obtained about brain functions by recording its electrical impulses in an electroencephalogram. ( This is possible even though the brain is extremely complex, even when compared with the most advanced modern computers.)
* Vision. Most people consider vision to be their most important sense. Vision is covered in chapter 15 as one application of the general physics of optics. Among the aspects of vision that have their explanation in the laws of physics are how the eye forms an image on the retina and the correction of common vision defects. The laws of optics, which applied in chapter 14 to lenses, mirrors, and microscopes, can also describe the near miracle of vision.
* From microwave Deep Heating to Sun Lamps. These are but two examples of application of electromagnetic ( EM) waves. EM waves take many forms, including radio waves, microwaves, visible light, ultraviolet ( as from a sunlamp), and gamma rays. The behavior of all these EM waves is analogous to that of sound waves. Learning the essential physics behind EM waves will make it possible to understand why they exhibit so many different properties. For example, the microwaves can be used for deep heating, while ultraviolet waves cannot, ultraviolet waves cause both tanning and sunburn and can be used to sterilize objects even if re very dim.
* Spectroanalysis. Spectroanalysis is a useful tool in detection of trace amounts of toxic substances. Spectroanalysis is based on the fact that all elements and compounds emit EM spectra that re uniquely characteristic of the particular substance. The uniqueness of atomic spectra is explained by atomic physics (chapter 17). Spectroanalysis is used in medicine and a host of other disciplines, from chemistry to astronomy. It was used as a tool long before atomic physics was understood.
* X rays. X-rays are a part of the EM spectrum that will be studied in chapter 16 and 17. As in the immediately preceding discussion of microwaves and ultraviolet waves, it will be possible to understand why x rays have the properties they do and why they are so useful as a diagnostic tool in medicine. The study of the effects of radiation
(chapter 18) will show that x rays are hazardous and cannot be made perfectly safe – that is, their use involves calculated risk.
* Radiotherapy, Radiation Diagnostics, and Radiation Protection. Chapter 18 starts with radioactivity and nuclear physics. It then applies nuclear physics and principles of physics studied earlier to such things as radiotherapy, radiation diagnostics, and radiation protection. It will be possible to understand the uses as well as the hazards of radiation. The energy and other characteristics of radiation and the physical laws governing it give insight into these problems and help one gain the ability to assess for oneself the risk versus the benefit.
THE DOMAIN OF PHYSICS
A. According to size of objects studied
1. Quantum domain – the domain of small objects. Objects are considered small if their sizes are
comparable to or smaller than the size of an atom.
2. Non-quantum domain – the domain of large objects. Objects are considered large if they are larger than the size of an atom.
B. According to speed of objects studied
1. Relativistic domain – the domain at high speed, that is if the speed of the moving object is comparable to
the speed of light.
2. Non-relativistic domain – the domain at low speed, that is the speed of the moving object is less than the
C. Newtonian domain – a combination of the division according to size and speed. It is the domain of large
objects at low speeds, the one we deal in our daily lives. (In honor of Sir Isaac Newton, the 17th century
D. Mechanics – is the study of the relation between the force and the resulting motion. It seeks to account
quantitatively for the motion of objects having given properties in terms of the force acting on them.
1. Newtonian mechanics – is the mechanics of the Newtonian domain. It deals with systems containing
objects which are large and which move at low speed.
- Relativistic mechanics – is the mechanics of the relativistic domain. In 1905, Einstein showed that a
different approach was necessary for the study of objects moving at speeds so high as to be comparable
to the speed of light.
3. Quantum mechanics – is the mechanics of the quantum domain. It was developed about the same time
with relativistic mechanics by Max Planck, Louis de Broglie, Erwin Schrodinger and others. They found
out that the Newtonian mechanics could not explain the motion of objects whose size is in the atomic
scale or smaller.
E. Electromagnetism – is the study of the properties and consequences of the electromagnetic force, which is
one of the fundamental forces in nature. The fundamental forces are gravitational force, electromagnetic
force, strong nuclear force and weak nuclear force.
F. Solid-state physics is a branch of physics that deals with the properties of solids. A particular problem in
solid – state physics, for instance the properties of materials use in transistors, is solve by employing the
mechanics of whichever domain is most appropriate.
G. Heat and Thermodynamics
THE FUNDAMENTAL MEASURABLE QUANTITIES IN PHYSICS
1. Length 3. Time 5. Luminous intensity 7. Molecular quantity
2. Mass 4. Temperature 6. Electric charge ( current )
THE FUNDAMENTAL MEASURABLE QUANTITIES IN MECHANICS
1. Length 2. Mass 3. Time
Measurement is a scientific comparison between an unknown quantity to a fixed known quantity called standard.
Systems of Measurement
1. English system (British Engineering system) – originated in England
2. Metric system – originated in France
Systeme International d’Unites ( SI ) adopted by the International Bureau of Weights and Measures in 1960.
The units of the MKS is adopted as the base units of the SI system.
Base Units of each System of measurement
Measurable Quantities in Mechanics
|
Metric System
|
English System
| |
CGS
|
MKS
|
FPS
| |
Length
|
Centimeter ( cm )
|
Meter ( m )
|
Foot ( ft )
|
Mass
|
Gram ( g )
|
Kilogram (kg )
|
Slug ( lbm )
|
Time
|
Second ( s )
|
Second ( s )
|
Second ( s )
|
Reasons for adopting the Metric system:
1. It is scientifically planned.
2. It is a decimal system.
3. It is universally accepted.
DISADVANTAGES OF THE ENGLISH SYSTEM
1 yard = ( King Henry I ) distance from the tip of his nose to the end of his thumb
1 inch ( 1324 ) = length of three grains of barleycorns laid end to end
1 mile = 1000 double step of an average soldier
1 foot = length of the foot of the king
THE CONCEPT OF THE METER
To be discuss in class with demonstrations
MAKING AND RECORDING MEASUREMENTS
Reasons for uncertainty in Measurements
1. The limitations inherent in the measuring instrument.
2. The conditions under which the measurement was made.
3. The different ways under which the person uses or reads the measuring instrument.
Terminologies:
- Fundamental or base unit – the standard unit for length, mass and time.
- Derived unit a combination of any of the three fundamental base units; i. e. m/s, m/s2, ft2, m3 etc.
- Accuracy – refers to the closeness of a measurement to the standard value for a specific physical quantity. It is express either as an absolute error or relative error.
- Absolute error ( EA ) is the actual difference between the observed ( O ) or measured value and the accepted value ( A ).
EA = | O – A |
- Relative error ( ER ) I expressed as a percentage error and is often called a percentage error.
ER = EA/A
- Absolute deviation ( DA ) is the difference between a single measured value ( O ) and the average ( M ) of several measurements made in the same way.
DA = | O – M |
- Relative deviation ( DR ) is the percentage average deviation of a set of measurements.
DR = DA / M
- Precision is the agreement among several measurements that have made in the same way. It tells how much reproducible the measurements are and is express in terms of the deviation.
- Tolerance is the degree of precision obtainable in a measuring instrument.
- Significant figure are those digits in a number that are known with certainty plus the digit that is uncertain.
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