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Basic Physics Quantities

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Discuss basic and derived units and measurements
Estimate the physical quantities
Explain Newton’s laws of motion
Explain Scalar and Vector

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Basic Physics Quantities

  1. 1. The purpose of the session • Discuss basic and derived units and measurements • Estimate the physical quantities • Explain Newton’s laws of motion • Explain Scalar and Vector
  2. 2. The International System of Units (SI) The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units are derived. The SI base units and their physical quantities are: • metre (m) for length • kilogram(kg) for mass • second(s) for time • ampere (A)for electric current • Kelvin(K) for temperature • Candela(cd) for luminous intensity • Mole(mol) for the amount of substance Symbols are written in lowercase except when named after person.
  3. 3. Unit of length m The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. 1 ⁄ 10,000,000 of the distance from the Earth's equator to the North Pole measured on the circumference through Paris Dimension symbol; L
  4. 4. Instruments
  5. 5. Unit of mass kg The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram. The mass of one litre of water. A litre is one thousandth of a cubic metre. Dimension symbol; M
  6. 6. Unit of Time s The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. The day is divided in 24 hours, each hour divided in 60 minutes, each minute divided in 60 seconds. A second is 1 ⁄ (24 × 60 × 60) of the day. Dimension symbol T
  7. 7. Unit of electric current A The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per meter of length. The original "International Ampere" was defined electrochemically as the current required to deposit 1.118 milligrams of silver per second from a solution of silver nitrate. Compared to the SI ampere, the difference is 0.015%. Dimension symbol; l
  8. 8. Electric Current A
  9. 9. Unit of thermodynamic temperature K The Kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The Celsius scale: the Kelvin scale uses the degree Celsius for its unit increment, but is a thermodynamic scale (0 K is absolute zero). Dimension symbol; θ
  10. 10. Unit of amount of substance mol The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol.“ When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. Atomic weight or molecular weight divided by the molar mass constant, 1 g/mol. Dimension symbol; n
  11. 11. Unit of luminous intensity cd The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. The candlepower, which is based on the light emitted from a burning candle of standard properties. Dimension symbol; J
  12. 12. Derived Units The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived. Each of these other units (SI derived units) is either dimensionless or can be expressed as a product of (positive or negative, but usually integral) powers of one or more of the base units.
  13. 13. Derived Units Name Symbol Quantity SI equivalency Hertz Hz frequency s−1 Radian rad, angle dimensionless Newton N force, weight kg⋅m⋅s−2 Pascal Pa pressure, stress kg⋅m−1⋅s−2 Joule J energy, work, heat kg⋅m2⋅s−2 watt W power, radiant flux kg⋅m2⋅s−3 coulomb C electric charge s⋅A volt V voltage, electrical potential difference, electromotive force kg⋅m2⋅s−3⋅A−1 farad F electrical capacitance kg−1⋅m−2⋅s4⋅A2 ohm Ω electrical resistance, impedance, reactance kg⋅m2⋅s−3⋅A−2
  14. 14. SI prefixes A SI prefix is a name that is added to the name of a basic unit and which indicates whether that unit is a multiple (or a fraction) of that unit. For example, the prefix "kilo“ added to "meter" gives "kilometer", which is a unit 1 000 times LARGER than the base unit "meter". Similarly, the prefix "milli" added to "gram" gives "milligram", which is a unit 1 000 times SMALLER than the base unit "gram". The table shown next slide lists the names of approved SI prefixes.
  15. 15. SI prefixes
  16. 16. Physical Quantity A physical quantity (or "physical magnitude") is a physical property of a phenomenon, body, or substance, that can be quantified by measurement. A physical quantity can be expressed as the combination of a number – usually a real number – and a unit or combination of units; for example, 1.6749275×10−27 kg (the mass of the neutron), or299792458 metres per second (the speed of light).
  17. 17. Newton's laws of motion Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They have been expressed in several different ways, over nearly three centuries,and can be summarised as follows.
  18. 18. First law: When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force. The first law can be stated mathematically as Consequently, An object that is at rest will stay at rest unless a force acts upon it. An object that is in motion will not change its velocity unless a force acts upon it.
  19. 19. Second law: The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object: F = ma. The net force on an object is equal to the rate of change (that is, the derivative) of its linear momentum p in an inertial reference frame:
  20. 20. Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body. The third law states that all forces between two objects exist in equal magnitude and opposite direction: if one object A exerts a force FA on a second object B, then B simultaneously exerts a force FB on A, and the two forces are equal and opposite: FA = −FB. The third law means that all forces are interactions between different bodies, and thus that there is no such Thing as a unidirectional force or a force that acts on only one body.
  21. 21. Scalar and Vector
  22. 22. Properties of vectors • Two vectors are equal if they have the same magnitude and the same direction. • Just like scalars which can have positive or negative values, vectors can also be positive or negative. A negative vector is a vector which points in the direction opposite to the reference positive direction. For example, if in a particular situation, we define the upward direction as the reference positive direction, then a force F1−→=30 N downwards would be a negative vector and could also be written as F1−→=−30 N. In this case, the negative (-) sign indicates that the direction of F1−→ is opposite to that of the reference positive direction. • A negative vector is a vector that has the opposite direction to the reference positive direction.
  23. 23. Addition and Subtraction of Vectors
  24. 24. Resultant of Forces
  25. 25. Multiplication of vector
  26. 26. Multiplication of Vector
  27. 27. Dot Product
  28. 28. Cross Product

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