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The METRIC system was standardized in France between 1791 and 1795, the imperial system in ENGLAND 1824.

The metric system was standardized in France between 1791 and 1795, the imperial system in England 1824.

SYSTEMS of UNITS BASED on arbitrary unit VALUES, formalized as standards, some unit values occur naturally in SCIENCE, systems of units based on these are called natural units.

Systems of units based on arbitrary unit values, formalized as standards, some unit values occur naturally in science, systems of units based on these are called natural units.

The units of length, MASS, time, temperature, electric CURRENT, LIGHT intensity and amount of SUBSTANCE are called base units.

The units of length, mass, time, temperature, electric current, light intensity and amount of substance are called base units.

The TENDENCY of an object to OPPOSE any alteration in its state of rest or a uniform MOTION is called INTERIA.

The tendency of an object to oppose any alteration in its state of rest or a uniform motion is called interia.

It is ZERO, because G = 0 in SPACE.

It is zero, because g = 0 in space.

Mass: It is the quantity of MATTER contained in the object. It is a constant quantity. It is measured in kilogram. It is a scalar quantity. It is measured by the physical BALANCE.

Weight: It is the FORCE with which the body is pulled towards the EARTH. It is not a constant quantity. It is measured in newton. It is a vector quantity. It is measured by a spring balance.

Mass: It is the quantity of matter contained in the object. It is a constant quantity. It is measured in kilogram. It is a scalar quantity. It is measured by the physical balance.

Weight: It is the force with which the body is pulled towards the earth. It is not a constant quantity. It is measured in newton. It is a vector quantity. It is measured by a spring balance.

Weight is the FORCE with which a body is pulled towards the earth. It is the product of the MASS and the ACCELERATION due to gravity at that place.

Weight is the force with which a body is pulled towards the earth. It is the product of the mass and the acceleration due to gravity at that place.

A unit or DISTANCE in astronomy in the solar SYSTEM. It is equal to approximately 1.496 * 1011 METRE. That is the MEAN distance of sun from earth.

A unit or distance in astronomy in the solar system. It is equal to approximately 1.496 * 1011 metre. That is the mean distance of sun from earth.

A TYPE of CALORIMETER MEASURING the heat evolved by the combustion of a FUEL.

A type of calorimeter measuring the heat evolved by the combustion of a fuel.

A UNIT used to express the intensity of a sound WAVE. It is measured on a logarithmic SCALE.

A unit used to express the intensity of a sound wave. It is measured on a logarithmic scale.

The difference in amplitude between the quietest SOUNDS and sounds so loud they HURT is almost too GREAT to write down in numbers. The DECIBEL scale is an EXAMPLE of a logarithmic scale.

The difference in amplitude between the quietest sounds and sounds so loud they hurt is almost too great to write down in numbers. The decibel scale is an example of a logarithmic scale.

1. To DETERMINE the thickness of a PIECE of matter.
2. RADAR (RADIO detection and ranging), to determine the distance of an aeroplane from radar station.
3. SONAR (Sound Navigation and Ranging), to determine distance of a submarine, in non - destructive, mechanical testing of MATERIALS.

Mass of an object is the QUANTITY of matter CONTAINED in the objects. It is the basic property of matter. It is a CONSTANT quantity i.e. it does not depend upon temperature, pressure and LOCATION of the object in SPACE.

Mass of an object is the quantity of matter contained in the objects. It is the basic property of matter. It is a constant quantity i.e. it does not depend upon temperature, pressure and location of the object in space.

To find out the distance between moon and earth, we send a radar signal from earth which will be reflected from the SURFACE of moon back to the receiver. If the time between SENDING and RECEIVING of the signal be “ t ” and “ V ” be the velocity of the signal, the distance between moon and the earth is v * t / 2. A radar signal travels with the velocity of light i.e. equal to 3 * 108 m/s.

To find out the distance between moon and earth, we send a radar signal from earth which will be reflected from the surface of moon back to the receiver. If the time between sending and receiving of the signal be “ t ” and “ v ” be the velocity of the signal, the distance between moon and the earth is v * t / 2. A radar signal travels with the velocity of light i.e. equal to 3 * 108 m/s.

The apparent SHIFT of a body with respect to another, with the shift of eye is called parallax. The nearer body ALWAYS appears to move in a DIRECTION OPPOSITE to that of the eye.

The apparent shift of a body with respect to another, with the shift of eye is called parallax. The nearer body always appears to move in a direction opposite to that of the eye.

1. ANGULAR DISTANCE METHOD
2. PARALLAX method
3. REFLECTION Method

• MICRON. 1 Micron = 10-6
• Mill micron. 1 Mill micron = 10-9
• Angstrom UNIT ( A ). 1 A = 10-10
• Fermi. (F) 1 f = 10-15

• PARSEC (PARALLACTIC SECOND)
• 1 parsec = 3.08 * 1016m

• Light year; 1 light year = 9.46 * 1015 METRES
• Astronomical units ( A.U ) ; 1 A.U= 1.496 * 1011 metres , One Astronomical Unit ( A.U ) is the DISTANCE between the earth and the SUN.

When it is not possible to measure a particular distance by its direct comparison with a CERTAIN STANDARD, we need indirect methods. We need indirect methods when the distance to be measured is EITHER too LARGE or too small.

When it is not possible to measure a particular distance by its direct comparison with a certain standard, we need indirect methods. We need indirect methods when the distance to be measured is either too large or too small.

A PARTICULAR PHYSICAL quantity expressed in a bigger unit has a SMALLER MAGNITUDE and vice versa.

A particular physical quantity expressed in a bigger unit has a smaller magnitude and vice versa.

The distance of SEPARATION between two POINTS in SPACE is called LENGTH.

The distance of separation between two points in space is called length.

All the units are well defined and easily reproducible at the entire place. All the units do not change with TIME, place, pressure, temperature etc., because they depend upon some FUNDAMENTAL property of the atom. In S.I system the unit of ENERGY (all FORMS) is joule and watt as the unit of power.

All the units are well defined and easily reproducible at the entire place. All the units do not change with time, place, pressure, temperature etc., because they depend upon some fundamental property of the atom. In S.I system the unit of energy (all forms) is joule and watt as the unit of power.

This system is now internationally ACCEPTED. It stands for the system International d’ units. These are the metre (m) for length, the kilogram (kg) for mass, the second (s) for the TIME, KELVIN (k) for temperature, ampere (A) for the current, candela (CD) for light intensity and MOLE (mol) for amount of substance. This system is used by almost all the countries of the world.

This system is now internationally accepted. It stands for the system International d’ units. These are the metre (m) for length, the kilogram (kg) for mass, the second (s) for the time, Kelvin (k) for temperature, ampere (A) for the current, candela (cd) for light intensity and mole (mol) for amount of substance. This system is used by almost all the countries of the world.

It is BASED upon the THREE BASIC units, the metre, the kilogram and the second for the length, the MASS and the time respectively.

It is based upon the three basic units, the metre, the kilogram and the second for the length, the mass and the time respectively.

It is based on three BASIC UNITS, the foot, the pound and the second for the length, the MASS and the TIME, RESPECTIVELY.

It is based on three basic units, the foot, the pound and the second for the length, the mass and the time, respectively.

It is based UPON three basic units, the CENTIMETER, the gram and the second for the length, the MASS and the time MEASUREMENTS RESPECTIVELY.

It is based upon three basic units, the centimeter, the gram and the second for the length, the mass and the time measurements respectively.

The COMMON SYSTEMS are the C.G.S. SYSTEM, the F.P.S system, the M.K.S system, and the S.I. system.

The common systems are the C.G.S. system, the F.P.S system, the M.K.S system, and the S.I. system.

There are seven physical quantities i.e. length, mass, time, ELECTRIC current, temperature, LIGHT intensity, and AMOUNT of SUBSTANCE are called fundamental physical quantities.

There are seven physical quantities i.e. length, mass, time, electric current, temperature, light intensity, and amount of substance are called fundamental physical quantities.

The measurement of physical QUANTITY is NECESSARY because WITHOUT it, we can’t study the characteristic features of the PROBLEM.

The measurement of physical quantity is necessary because without it, we can’t study the characteristic features of the problem.

The REFERENCE STANDARD for MEASUREMENT is CALLED UNIT.

The reference standard for measurement is called unit.