ADVANTAGES AND DISADVANTAGES OF FRICTION - METHODS OF REDUCING FRICTION

ADVANTAGES AND DISADVANTAGES OF FRICTION - METHODS OF REDUCING FRICTION

ADVANTAGES OF FRICTIONFriction plays a vital role in our daily life. Without friction we are handicap. 1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it     becomes difficult to walk due to low friction of ice. 2. We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail. 3. A horse can not pull a cart unless friction furnishes him a secure Foothold. DISADVANTAGES OF FRICTION Despite the fact that the friction is very important in our daily life, it also has some disadvantages like: 1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way     some useful energy is wasted as heat energy. 2. Due to friction we have to exert more power in machines. 3. It opposes the motion. 4. Due to friction, noise is also produced in machines. 5. Due to friction, engines of automobiles consume more fuel which is a money loss. METHODS OF REDUCING FRICTIONThere are a number of methods to reduce friction in which some are discussed here. USE OF LUBRICANTS:The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity. USE OF GREASE:Proper greasing between the sliding parts of machine reduces the friction. USE OF BALL BEARING:In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings. DESIGN MODIFICATION:Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.

FORCE & MOTION

"Force is an agent which changes or tends to change the state  of rest or of uniform motion of a body."
In the light of Newton's 2nd law of motion Force may be defined as :
"Force acting on a body is equal to the product of the mass and acceleration produced in the body."
i.e.
F = ma
Force can accelerate or decelerate a body.  Force is a vector quantity.
UNITS OF FORCE
(i) NEWTON (N) in S.I system    (ii) DYNE in C.G.S system    (iii) POUND (Lb) in BRITISH ENGINEERING SYSTEM (F.P.S)
NEWTON
Newton is the unit of force and can be defined as:
"The amount of force that produces an acceleration of 1 m/s2 in a body of mass 1-kg is equal to 1 NEWTON."
1 N = 1 kg x 1m/s2
[ N = kg m/s2]
NEWTON 'S FIRST LAW OF MOTION
STATEMENT:    Newton 's first law of motion states that:
"Every body remains at rest or continues to move with uniform velocity in straight line unless an unbalanced force acts upon it".
EXPLANATION
First law of motion consists of two parts:
PART NO 1:
The first part states that a body at rest remains at rest unless an unbalanced force acts upon it.    This part is in accordance with our common experience for example, a book lying on a table remains at    rest unless it is lifted or pushed by an external force.
PART NO 2 :
Second part states that a body in motion remains in motion with uniform velocity unless an unbalance    force acts upon it. This part is not self-evident because a ball pushed once does not continue its motion    forever. A little consideration however, shows that there is an opposing force like ground friction and air    friction acting in this case. These frictional forces are responsible to stop the ball. If we eliminate these    opposing forces, a body in motion will continue its motion forever.
INERTIA
"Tendency of a body by virtue of which the body at rest or moving with uniform velocity retains its state is called INERTIA."
OR
"Property of a body by which a body resists a force, applied to it to change its state of rest or of uniform velocity is called INERTIA."
INERTIA of a body is directly related to its mass. Heavy bodies have greater inertia while lighter bodies    have little inertia.
LAW OF INERTIA AND THE FIRST LAW OF MOTION
Every body in the universe opposes the force which tends to change its state of rest or of uniform    motion. This property INERTIA is a direct consequence of FIRST LAW OF MOTION. As heavy bodies due    to greater INERTIA requires forces of large magnitude and bodies of small masses require small forces.    By the above explanation of INERTIA we conclude that the state of rest or motion does not change by its    self unless an external force acts upon it, which is according to the FIRST LAW OF MOTION.    Thus the FIRST LAW OF MOTION is also called LAW OF INERTIA.

DISTRIBUTIVE LAW FOR DOT PRODUCT

DISTRIBUTIVE LAW FOR DOT PRODUCT
According to distributive law for dot product:
	PROOF
	Consider three vectors , and .Here we will use geometric interpretation of dot product by drawing projection as shown below. First we obtain the sum of vectors  and by head to tail rule then we draw projection  and from the terminal point of vector respectively onto the direction of . The dot product  is equal to the projection of vector  onto the direction of  multiplied by the magnitude of. i.e.

SCALARS & VECTORS

SCALAR QUANTITIES
Physical quantities which can completely be specified by a number (magnitude) having an appropriate unit are known as "SCALAR QUANTITIES".
Scalar quantities do not need direction for their description. Scalar quantities are comparable only when they have the same physical dimensions. Two or more than two scalar quantities measured in the same system of units are equal if they have the same magnitude and sign. Scalar quantities are denoted by letters in ordinary type. Scalar quantities are added, subtracted, multiplied or divided by the simple rules of algebra.
	EXAMPLES
	Work, energy, electric flux, volume, refractive index, time, speed, electric potential, potential difference, viscosity, density, power, mass, distance, temperature, electric charge, electric flux etc.
	VECTORS QUANTITIES
	Physical quantities having both magnitude and direction with appropriate unit are known as "VECTOR QUANTITIES".
	We can't specify a vector quantity without mention of deirection.  vector quantities are expressed by using bold letters with arrow sign such as: vector quantities can not be added, subtracted, multiplied or divided by the simple rules of algebra. vector quantities added, subtracted, multiplied or divided by the rules of trigonometry and geometry.
	EXAMPLES
	Velocity, electric field intensity, acceleration, force, momentum, torque, displacement, electric current, weight, angular momentum etc.
	REPRESENTATION OF VECTORS
	On paper vector quantities are represented by a straight line with arrow head pointing the direction of vector or terminal point of vector.
	A vector quantity is first transformed into a suitable scale and then a line is drawn with the help of the
	scale choosen in the given direction.

Chemical Names

Systematic and Common Names

There are many ways to name a chemical. Here is a look at the difference between different types of chemical names, including systematic names, common names, vernacular names and CAS numbers.

Systematic or IUPAC Name

The systematic name, also called the IUPAC name is the preferred way to name a chemical because each systematic name identifies exactly one chemical. The systematic name is determined by guidelines set forth by the International Union of Pure and Applied Chemistry (IUPAC).

Common Name

A common name is defined by the IUPAC as a name that unambiguously defines a chemical, yet does not follow the current systematic naming convention. An example of a common name is acetone, which has the systematic name 2-propanone.

Vernacular Name

A vernacular name is a name used in a lad, trade or industry that does not unambiguously describe a single chemical. For example, copper sulfate is a vernacular name which may refer to copper(I) sulfate or copper(II) sulfate.

Archaic Name

An archaic name is an older name for a chemical that predates the modern naming conventions. It's helpful to know archaic names of chemicals because older texts may refer to chemicals by these names. Some chemicals are sold under archaic names or may be found in storage labeled with the older names. An example of this is muriatic acid, which is the archaic name for hydrochloric acid and is one of the names under which hydrochloric acid is sold.

CAS Number

A CAS number is an unambiguous identifier assigned to a chemical by the Chemical Abstracts Service (CAS), a part of the American Chemical Society. CAS numbers are assigned sequentially, so you can't tell anything about the chemical by its number. Each CAS number consists of three strings of numbers that are separated by hyphens. The first number contains up to six digits, the second number is two digits, and the third number is a single digit.

Other Chemical Identifiers

Although the chemical names and CAS Number are the most common way to describe a chemical, there are other chemical identifiers you may encounter. Examples include numbers assigned by PubChem, ChemSpider, UNII, EC number, KEGG, ChEBI, ChEMBL, RTES number and the ATC code.

Example of Chemical Names

Putting it all together, here are the names for CuSO4·5H2O:

Systematic (IUPAC) Name: copper(II) sulfate pentahydrate

Common Names: copper(II) sulfate, copper(II) sulphate, cupric sulfate, cupric sulphate

Vernacular Name: copper sulfate, copper sulphate

Archaic Name: blue vitriol, bluestone, copper vitriol

Periodic Table Notes and Review

Periodic Table Notes and Review

The periodic table is an important tool in chemistry. These notes review the periodic table, how it is organized, and periodic table trends.

Invention and Organization of the Periodic Table

In 1869, Dmitri Mendeleev organized the chemical elements into a periodic table much like the one we use today, except his elements were ordered according to increasing atomic weight, while the modern table is organized by increasing atomic number. The way the elements are organized makes it possible to see trends in element properties and to predict the behavior of elements in chemical reactions.

Rows (moving left to right) are called periods. Elements in a period share the same highest energy level for an unexcited electron. There are more sublevels per energy level as atom size increases, so there are more elements in periods further down the table.

Columns (moving top to bottom) form the basis for element groups. Elements in groups share the same number of valence electrons or outer electron shell arrangement, which gives elements in a group several common properties. Examples of element groups are alkali metals and noble gases.

Periodic Table Trends or Periodicity

The organization of the periodic table makes it possible to see trends in properties of elements at a glance. The important trends relate to atomic radius, ionization energy, electronegativity, and electron affinity.

• Atomic Radius
  Atomic radius reflects the size of an atom. Atomic radius decreases moving from left to right across a period and increases moving from top to bottom down an element group. Although you might think atoms would simply become larger as they gain more electrons, electrons remain in a shell, while the increasing number of protons pulls the shells in closer to the nucleus. Moving down a group, electrons are found further from the nucleus in new energy shells, so the overall size of the atom increases.
• Ionization Energy
  Ionization energy is the amount of energy needed to remove an electron from an ion or atom in the gas state. Ionization energy increases moving from left to right across a period and decreases moving top to bottom down a group.
• Electronegativity
  Electronegativity is a measure of how easily an atom forms a chemical bond. The higher the electronegativity, the higher the attraction for bonding an electron. Electronegativitydecreases moving down an element group. Elements on the lefthand side of the periodic table tend to be electropositive or more likely to donate an electron than accept one.
• Electron Affinity
  Electron affinity reflects how readily an atom will accept an electron. Electron affinity varies according to element group. The noble gases have electron affinities near zero because they have filled electron shells. The halogens have high electron affinities because the addition of an electron gives an atom a completely filled electron shell.

Chemistry Notes and Review

Atomic and Molecular Structure

The building blocks of matter are atoms, which join together to form molecules or compounds. It's important to know the parts of an atom, what ions and isotopes are, and how atoms join together.

Parts of an Atom

Atoms are made up of three components:

• protons - positive electric charge
• neutrons - no electric charge
• electrons - negative electric charge

Protons and neutrons form the nucleus or center of each atom. Electrons orbit the nucleus. So, the nucleus of each atom has a net positive charge, while the outer portion of the atom has a net negative charge. In chemical reactions, atoms lose, gain, or share electrons. The nucleus does not participate in ordinary chemical reactions, although nuclear decay and nuclear reactions can cause changes in the atomic nucleus.

Atoms, Ions, and Isotopes

The number of protons in an atom determines which element it is. Each element has a one- or two-letter symbol that is used to identify it in chemical formulas and reactions. The symbol for helium is He. An atom with two protons is a helium atom regardless of how many neutrons or electrons it has. An atom may have the same number of protons, neutrons, and electrons or the number of neutrons and/or electron may differ from the number of protons.

Atoms that carry a net positive or negative electric charge are ions. For example, if a helium atom loses two electrons, it would have a net charge of +2, which would be written He2+.

Varying the number of neutrons in an atom determines which isotope of a element it is. Atoms may be written with nuclear symbols to identify their isotope, where the number of nucleons (protons plus neutrons) is listed above and to the left of an element symbol, with the number of protons listed below and to the left of the symbol. For example, three isotopes of hydrogen are:

11H, 21H, 31H

Since you know the number of protons never changes for an atom of an element, isotopes more commonly are written using the element symbol and the number of nucleons. For example, you could write H-1, H-2, and H-3 for the three isotopes of hydrogen or U-236 and U-238 for two common isotopes of uranium.

Atomic Number and Atomic Weight

The atomic number of an atom identifies its element and its number of protons. The atomic weight is the number of protons plus the number of neutrons in an element (because the mass of electrons is so small compared with that of protons and neutrons that it essentially doesn't count). The atomic weight sometimes is called atomic mass or the atomic mass number. The atomic number of helium is 2. The atomic weight of helium is 4. Note that the atomic mass of an element on the periodic table isn't a whole number. For example, the atomic mass of helium is given as 4.003 rather than 4. This is because the periodic table reflects the natural abundance of isotopes of an element. In chemistry calculations, you use the atomic mass given on the periodic table, assuming a sample of an element reflects the natural range of isotopes for that element.

Molecules

Atoms interact with each other, often forming chemical bonds with each other. When two or more atoms bond to each other, they form a molecule. A molecule can be simple, such as H2, or more complex, such as C6H12O6. The subscripts indicate the number of each type of atom in a molecule. The first example describes an molecule formed by two atoms of hydrogen. The second example describes a molecule formed by 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. While you could write the atoms in any order, the convention is to write the positively charged past of a molecule first, followed by the negatively charged part of the molecule. So, sodium chloride is written NaCl and not ClNa.