*Reference: Course on Subject Clearing*

This is the KHTK Glossary for PHYSICS. You can find out more about KHTK at **What is KHTK?** This glossary is to be used with Subject Clearing.

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## Key Concepts

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## Glossary

**ABSOLUTE VALUE**, **ACCELERATION**, **ADIABATIC PROCESS**

**BODY**, **BOLTZMANN CONSTANT**

** CARNOT CYCLE**,

**CASE OF CONSTANT ACCELERATION**,

**CONSISTENCY**,

**CONSCIOUSNESS**,

**COORDINATE SYSTEM**

**DISPLACEMENT**, **DISTANCE**

**ENERGY**, **ENERGY SUBSTANCE**, **ENTROPY**

**FORCE**, **FREELY FALLING BODIES**, **FUNCTION**

** GAS CONSTANT**,

**GRAVITY**,

**GRAPH**

** IDEAL GAS**,

**INERTIA,**,

**INTERNATIONAL SYSTEM OF UNITS (SI)****,**

**INVERSE FUNCTION**

**ISOTHERMAL PROCESS****KINEMATICS**

**LAWS OF THERMODYNAMICS**, **LINEAR EQUATION**

** MACROSTATES**,

**,**

**MASS****MATERIAL**,

**MATERIALISM**,

**MATERIAL SUBSTANCE**,

**MATHEMATICS**,

**MATTER**,

**MAXWELL-BOLTZMANN DISTRIBUTION**,

**MICROSTATES**,

**MOTION**

**ONE-DIMENSIONAL**

**PARTICLE**, ** PHYSICAL**,

**PHYSICS,**

**PRIMARY SUBSTANCE****QUANTUM “PARTICLES” **

**SCIENCE**, **SCIENTIFIC NOTATION**, **SIGNIFICANT FIGURES**, **SIMULTANEOUS EQUATIONS**, **SPECIFIC HEAT CAPACITY**, **SPECTRUM OF SUBSTANCE**, **SPEED**, **STANDARD**, **STATE VARIABLE**, **STATISTICAL THERMODYNAMICS**, **STATISTICS**, **SUBSTANCE, SYSTEM**

**THERMODYNAMIC CYCLE**, **THERMODYNAMIC EQUILIBRIUM**, **TIME**, **TRIGONOMETRIC FUNCTION**

**VARIABLES**, **VELOCITY**,

**UNITS**

# —A—

**ABSOLUTE VALUE**

The value without regards to its sign. It is the magnitude of a number.

**ACCELERATION**

Acceleration is the time rate of change of velocity.

The **average acceleration** is defined as,

Like velocity, acceleration can be positive, negative or zero.

**Instantaneous acceleration** is the acceleration of the particle at a given instant of time. It is determined by the slope of the tangent line to the v-t curve at any time. The instantaneous acceleration at time *t _{1}* is given by

**ADIABATIC PROCESS**

An adiabatic process occurs without transferring heat or mass between a thermodynamic system and its surroundings. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work. It also conceptually forms the foundation of the theory used to expound the first law of thermodynamics and is therefore a key thermodynamic concept. Q = 0 but ΔT ≠ 0.

# —B—

**BODY**

Body is any mass, especially one considered as a whole.

**BOLTZMANN CONSTANT**

It is the proportionality factor that relates the average relative kinetic energy of particles in a gas with the thermodynamic temperature of the gas.

# —C—

**CARNOT CYCLE**

The Carnot cycle is a thermodynamic cycle. When acting as a heat engine, it consists of the following steps:

- Isothermal Expansion. Heat is transferred reversibly from high temperature reservoir at constant temperature Th (isothermal heat addition or absorption).
- Isentropic (reversible adiabatic) expansion of the gas (isentropic work output).
- Isothermal Compression. Heat transferred reversibly to low temperature reservoir at constant temperature Tc. (isothermal heat rejection).
- Adiabatic reversible compression.

Essentially, there are two “heat reservoirs” forming part of the heat engine at temperatures Th and Tc (hot and cold respectively). They have such large thermal capacity that their temperatures are practically unaffected by a single cycle.

Since the cycle is theoretically reversible, entropy is conserved. During the cycle, an amount of energy ThΔS is extracted from the hot reservoir and a smaller amount of energy TcΔS is deposited in the cold reservoir. The difference in the two energies (Th-Tc)ΔS is equal to the work done by the engine. Thus, heat is converted into work.

**CASE OF CONSTANT ACCELERATION**

For a particle starting at origin, x = 0, t = 0, and v = v_{0}. Also, x = displacement from origin, and t = time elapsed.

**CONSISTENCY**

Consistency refers to degree of density, firmness, viscosity, etc. For example, “*The liquid has the consistency of cream.”*

**CONSCIOUSNESS**

Consciousness is the ability to sense. There is primitive consciousness only, “to evolve”, in the “primary substance.” This leads to evolution. As the substance and its form evolve, its consciousness also evolves. This consciousness is weak in inanimate objects, greater in animate organisms, and the greatest in the humankind. There is no consciousness independent of the universe. The common denominator of all consciousness is “to evolve.” The ultimate evolved consciousness is yet to be realized. It is possible that, over the millennia, many individuals may have evolved to the ultimate consciousness; but the humankind and the universe as a whole have yet to evolve to that state.

**COORDINATE SYSTEM**Origin: “order together.” A coordinate system is a fixed system of directions and angles from an ‘origin point’ that uses numbers to define the position of a point, line, or the like.

# —D—

**DISPLACEMENT**Displacement is the measure of the position of the object in a coordinate system.

**Absolute displacement**specifies a particle’s location as measured from the origin. It has both a magnitude and a sign. Its magnitude is the straight-line distance from the origin to the location of a particle. Its sign is positive if the particle is on the positive side of the axis, and negative if it is on the negative side.

**Relative displacement**is the location of the particle as measured from an

*arbitrary*point. Like absolute displacement, relative displacement can be either positive or negative. If right is chosen as the positive direction, then the relative displacement is negative when the position of the particle is to the left of the position from which it is measured.

**DISTANCE**Distance is the absolute value of the relative displacement. Therefore, the distance traveled is always positive.

# —E—

**ENERGY**

- Origin: “to be active.” Energy is the capacity for vigorous activity; available power. The substance of light is called energy because of its extreme speed.
- Energy is a substance that is made up of flows rather than discrete units. It does not have the property of center of mass. But, energy has a variable consistency that gives us the electromagnetic spectrum.

**ENERGY SUBSTANCE**

The energy substance is that which fills the atom beyond its nucleus. It is not solid. It is more like “liquid” because it is the material substance thinned out thousands of times. From electron to microwave we have continually thinning substance. Light has substance because it has momentum that can be sensed and measured. Energy substance does not have center of mass, therefore, there are no discrete energy particles. The concept of energy quanta relates to the consistency of energy substance and how it is sensed through interactions.

**ENTROPY**

The word ‘entropy’ comes from the Greek words, `en-tropie’ (intrinsic direction). The concept of entropy came about from investigations into lost energy in heat engines. Entropy was introduced as the concept of ‘transformation-energy’, i.e. energy lost to dissipation and friction. Entropy is a macro state variable for a system that is defined only when the system is in equilibrium.

1789 Count Rumford – heat could be created by friction as when cannon bores are machined.

1803 Lazare Carnot – Losses of moments of activity

1824 Sadi Carnot – Work or motive power can be produced when heat falls through temperature difference

1843 James Joules – expresses the concept of energy and its conservation in all processes. He is unable to quantify the effects of friction and dissipation.

1850s Rudolf Clausius – objected to the supposition that no change occurs in the working body. There is inherent loss of usable heat when work is done, e.g. heat produced by friction. This was in contrast to earlier views, based on the theories of Isaac Newton, that heat was an indestructible particle that had mass.

1877 – Boltzmann – visualized a probabilistic way to measure the entropy of an ensemble of ideal gas particles

Entropy is a state variable. Its thermodynamic definition is “Q/T,” and its statistical mechanics definition is “k ln Ω.” Essential problem in statistical thermodynamics has been to determine the distribution of a given amount of energy E over N identical systems.

# —F—

**FORCE**

Origin: “strong.” Force is an influence on a body or system, producing or tending to produce a change in movement or in shape or other effects.

**FREELY FALLING BODIES**A body falling freely under gravitation has

- Constant downward acceleration (g) of 9.81 m/s
^{2}, or 32.2 ft/ s^{2} - Negligible air resistance.

**FUNCTION**

Origin: “performed, executed.” A function is a mathematical relationship between two variables. If one of the variables takes on a particular value, the relationship tells us the corresponding value of the other variable.

# —G—

**GAS CONSTANT**

The gas constant R is a physical constant that is featured in many fundamental equations in the physical sciences, such as the ideal gas law. It relates the energy scale to the temperature scale, when a mole of particles at the stated temperature is being considered. It is defined as the Avogadro constant multiplied by the Boltzmann constant.

**GRAVITY**

Gravity is substantial enough to be perceived as force. Therefore, gravity is a substance that is different from matter and energy.

**GRAPH**

Whenever one has a mathematical relationship between two variables, one can represent the function by a two dimensional graph. **[Page 3 – axes, origin, independent variable, dependent variable, slope, intercept]**

# —H—

# —I—

**IDEAL GAS**The volume of ideal gas is essentially made up of electromagnetic substance. At very high pressures and very low temperatures the Ideal gas approximations are not valid.

**INERTIA**

Inertia is the property of substance that resists any perturbation.

**INTERNATIONAL SYSTEM OF UNITS (SI)**

The set of units most commonly used throughout the world, and which is almost exclusively used in scientific work. In mechanics, the units are the meter, the kilogram, and the second, and are what is commonly called the *mks* system.

**INVERSE FUNCTION**

A function gives us a y value for every x value. Inverse function turns it around and gives us an x value for every y-value. To get the graph of inverse function, rotate the graph of the function 90 deg clockwise so that y appears along the horizontal.

**ISOTHERMAL PROCESS**

An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change in the system will occur slowly enough to allow the system to continue to adjust to the temperature of the reservoir through heat exchange. ΔT = 0 but Q ≠ 0.

# —K—

**KINEMATICS**

Kinematics is the study of physical quantities that describe the motion of an object.

# —L—

**LAWS OF THERMODYNAMICS**

**FIRST LAW:**Energy cannot be created or destroyed, only transformed.

**LINEAR EQUATION**

Such equation are represented by straight lines on a graph.

# —M—

**MACROSTATES**

Pressure, temperature and volume are macrostates of a system.

**MASS**

Origin: “barley cake.” Mass is the quantity of matter as determined from its weight or from Newton’s second law of motion.

**MATERIAL**

Origin: “belonging to matter.” Material pertains to the substance or substances of which a thing is made or composed.

**MATERIALISM**

Materialism holds matter to be the fundamental substance in nature, and all things, including mental states and consciousness, are results of material interactions.

**MATERIAL SUBSTANCE**

The material substance comes in the forms of solids, liquids and gases. All of these forms of material substance can be reduced to discrete particles. These discrete material particles have a solid form and a center of mass. The ultimate material particles are protons and neutrons.

**MATHEMATICS**

Origin: “something learned.” Mathematics is the systematic treatment of magnitude, relationships between figures and forms, and relations between quantities expressed symbolically.

**MATTER**

Origin: “woody part of a tree.” Philosophy defines matter as that which by integrative organization forms chemical substances and living things. Matter seems to refer to *substance *in general. See SUBSTANCE.

**MAXWELL-BOLTZMANN DISTRIBUTION**

A **Maxwell**–**Boltzmann Distribution** is a probability **distribution** used for describing the speeds of various particles within a stationary container at a specific temperature. The **distribution** is often represented with a graph, with the y-axis defined as the number of molecules and the x-axis defined as the speed.

**MICROSTATES**

State of every atom and molecule.

**MOTION**

Origin: “to move.” Motion is the action or process of moving or of changing place or position.

# —O—

**ONE-DIMENSIONAL**One-dimensional means, in a straight line; in the same direction; along the x-axis.

# —P—

**PARTICLE**

- In Science, the definition of PARTICLE is missing. This word has been used in very general terms only. A MATERIAL PARTICLE in space is defined by its center of mass. An ENERGY PARTICLE is defined by the amount of substance participating in an interaction. A QUANTUM is a discrete amount drawn from a continuum by an interaction at the atomic level.
- In Mechanics, a particle is an infinitesimally small object located at a definite point in a coordinate system. The particle is the representation of the mathematical ‘center of mass’ of an object. If there is no center of mass, as in the case of a “light particle” then the laws of mechanics do not apply.
- Originally, a particle was understood to be a small part of matter that obviously had a fixed boundary and a center of mass. Example of this would be a dust particle, or a particle of sand. In Chemistry, a particle was related to the smallest part of substance that took part in chemical reactions. Ultimately, a particle of matter was reduced to the idea of an atom or a molecule. Its boundaries were considered to be well defined and fixed, and it had a center of mass.
- This idea of particle shifted as one looked at the sub-atomic region beyond the nucleus. Here the substance is no longer rigidly structured as in the case of matter, or even an atom. This sub-atomic substance is rather thin in consistency and spread out. It appears as a continuum with no definite boundaries and no center of mass. Only definite amount of this substance seem to take part in sub-atomic reactions. Therefore, we fall back to the concept of particle similar to that in Chemistry. It is a definite amount of “energy substance” that takes part in a reaction. At sub-atomic level, this is referred to as a “quantum.”
- In atomic physics, a particle is a high-energy pulse with an energy field forming its background. The particle maintains continuity with its background.
- In its most basic sense, a particle is defined in terms of its associations; a perceptual element.

**PHYSICAL**

Origin: “pertaining to nature.” Physical indicates connected with, pertaining to that which is material.

**PHYSICS**

Origin: “pertaining to nature.” Physics is the science that deals with matter, energy, motion, and force.

**PRIMARY SUBSTANCE**

The intellectual “substance-in-itself.” It is what a substance inherently is. In Hinduism, it is symbolized as SHIVA, which is then formed into substances through SHAKTI.

# —Q—

**QUANTUM “PARTICLES” **

Quantum “particles” are not really discrete particles; but they have a very high consistency like syrup. Quantum “particles” participate in discrete interactions like matter.

# —S—

**SCIENCE**

Origin: “to know.” Science is systematic knowledge of the physical or material world gained through observation and experimentation.

**SCIENTIFIC NOTATION**

Scientific notation is a method for expressing a given quantity as a number having significant digits necessary for a specified degree of accuracy, multiplied by 10 to the appropriate power, as 1385.62 written as 1.386 × 10^{3}.

**SIGNIFICANT FIGURES**

Whenever a measured value is given for a physical quantity, it can only be an approximation, because it is not possible to measure anything with “infinite” accuracy. A scientist or engineer who specifies the numerical value of a physical quantity keeps only as many figures in the number as are justified by the accuracy to which the physical quantity is known. For any measured quantity there is always some uncertainty in the last digit given. The number of significant figures provide a rough measure of percent uncertainty.

**SIMULTANEOUS EQUATIONS**

When we have two different relationships involving the same two variables, then both relationships can be valid only for specific values of the variables.

**SPECIFIC HEAT CAPACITY**

The specific heat capacity of a substance is the amount of energy that must be added, in the form of heat, to one unit of mass of the substance in order to cause an increase of one unit in its temperature. The SI unit of specific heat is joule per kelvin per kilogram, J/(K kg). Liquid water has one of the highest specific heats among common substances, about 4182 J/(K kg) at 20 °C. The specific heat often varies with temperature, and is different for each state of matter.

**SPECTRUM OF SUBSTANCE**

The primary substance evolves into thought substance (SPACE), energy substance (ENERGY), and material substance (MATTER) by gradual condensation. This process of evolution is essentially the process of forming. This process may be called TIME. This gives us the spectrum of substance.

**SPEED**

Average speed is defined as the total distance traveled in a given time divided by that time interval. Since distance traveled is always positive, the average speed is always positive. Its units are the same as those of velocity. Average speed is either equal to or greater than the average velocity. Instantaneous speed is always the same as instantaneous velocity.

**STANDARD**

The physical specimen, which defines the unit, is called the *standard*.

**STATE VARIABLE**

Internal energy, enthalpy, and entropy are state quantities or state functions because they describe quantitatively an equilibrium state of a thermodynamic system, irrespective of how the system arrived in that state. In contrast, mechanical work and heat are process quantities or path functions, because their values depend on the specific transition (or path) between two equilibrium states.

**STATISTICAL MECHANICS**

Statistical mechanics involves dynamics, Where the attention is focused on statistical equilibrium (steady state). Statistical equilibrium does not mean that the particles have stopped moving (mechanical equilibrium), rather, only that the ensemble is not evolving.

**STATISTICAL THERMODYNAMICS (equilibrium statistical mechanics)**

The primary goal of statistical thermodynamics is to derive the classical thermodynamics of materials in terms of the properties of their constituent particles and the interactions between them. In other words, statistical thermodynamics provides a connection between the macroscopic properties of materials in thermodynamic equilibrium, and the microscopic behaviors and motions occurring inside the material.

**STATISTICS**

We can’t keep track of trillions of molecules individually, so we track the average.

**SUBSTANCE**

Origin: “That which stands under.” A thing is made of *substance*. The substance is a spectrum that extends from tangible matter to intangible light to ephemeral thought. This whole spectrum of substance is substantial enough to be sensed one way or other. The substance may be divided broadly as material substance, energy substance and thought substance.

**SYSTEM**

Origin: “that stands together.” In physics, system refers to a physical structure considered as a whole.

# —T—

**THERMODYNAMIC CYCLE**

Every single thermodynamic system exists in a particular state. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. In the process of going through this cycle, the system may perform work on its surroundings, for example by moving a piston, thereby acting as a heat engine.

**THERMODYNAMIC EQUILIBRIUM**

Macrostates are not changing, but microstates are constantly changing. When a system changes state, the beginning and final states may be well-defined, but the intermediate states may not be defined because the system is not in equilibrium. However, if we can maintain equilibrium the whole time by making the changes very slowly and in very small steps (quasi-static process). Then we can describe the path from beginning and final states. Most quasi-static processes are reversible because there is no loss of energy. In real world there is no perfectly reversible process.

**THOUGHT SUBSTANCE**

The thought substance is the material substance thinned out trillions of times. It is more like “gaseous”. Its space is filling the universe almost. Here we see space also expanding and time becoming swifter compared to material space and time. We encounter “quantum entanglement” when thought (and energy) space and time are superimposed over material space and time.

**TIME**Time is a measure of when the object is at a certain position in a coordinate system. Time elapsed is always positive.

**TRIGONOMETRIC FUNCTION**

Trigonometric Functions are most usually defined in terms of ratios of sides of a right triangle, in which the angle plays the role of the independent variable.

# —U—

**UNITS**

Origin: “unity.” Unit is an identity element. We need **units of measurement** to measure physical quantities, such as, length, area, volume, velocity, acceleration, mass, time and temperature. Not all measurable quantities require their own units. Often, the unit is automatically defined in terms of other units. Such units are called **derived units**. In the subject of mechanics, only three physical quantities must have their units defined independently. These three quantities are usually taken to be length, mass and time, and their units are called ** fundamental units**. It turns out that units can be treated algebraically in any physics equation.

# —V—

**VARIABLES**

Variables are quantities that can take on a range of values.

**VELOCITY**Velocity is the time rate of change of displacement.

The **average velocity** is defined as,

Since the time difference in the denominator is always positive, the sign of average velocity is the sign of the relative displacement, and thus it indicates whether the particle has moved to the right (plus) or to the left (minus).

**Instantaneous velocity** is the velocity of the particle at a given instant of time. It is determined by the slope of the tangent line to the x-t curve at any time. The instantaneous velocity at time *t _{1}* is given by