physics part 1

• Objects in equilibrium may not have any

  • Force acting
  • Velocity
  • Acceleration
  • Torque acting upon it
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• Newton's law of gravitation


  Every body in the universe attracts every other body with a force, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres and directed along the line joining their centres
• Gravitational constant in M.K.S system
• When a body falls freely

  a = g
• An astronaut will feel comfortable at a distance of 10m from axis of rotation if the space craft is revolving about its axis at 9.6 Revolutions per minute
• At a depth equal to half the radius of the earth, the value of 'g' reduces to half its value on the surface of the earth
• At a distance of 1.41 times of radius of earth, the gravitational acceleration have half the value that it has on earth's surface
• Gravitational acceleration 'g'


  All the bodies fall downward with some acceleration as this acceleration is due to the gravitational force
• Gravitational constant 'G'


  If two bodies each of masses 1 kg are placed at a distance of 1m, then the force of attraction exists between them is equal to the gravitational constant
• The value of gravitational constant is very small, ie., 6.67 x 10^-11 Nm²/kg². So we cannot feel the force of attraction between the bodies around us
• The equation (i) expressing the law of gravitation in vector form which gives the direction as well as the magnitude
• In M.K.S system the value of 'G' (gravitational constant) is 6.67 x 10^-11 Nm²/kg
• The greater the value of 'h', the smaller is the value of 'g' or simply we can say that value of 'g' decreases with altitude
• Al-Razi wrote about two hundred (200) original monographs, half of which pertained to medicine
• Al-Beruni was the most famous scholar of the golden age of Islam. He wrote more than one hundred and fifty books on such subjects as Mathematics, Physics, History, Geography etc. He discussed the measurement of earth, the shape of earth, the movement of sun and moon. One of his famous books was Qanoon-ul-Masoodi. He also determined the density of metals
• Yaqoob Kindi worked on metrology, specific gravity and on tides, but his most important work was on optics and refraction. He also constructed pinhole camera
• Ibn-e-Sina worked a lot in medicine. He also wrote Al-Shifa, an Encyclopedia of Philosophy
• Dr. Abdus Salam established the International Center for Theoretical Physics at Trieste. He was awarded the Nobel Prize in Physics in 1979 for his work on Grand Unification Theory (GUT)
• Dr. Abdul Qadeer Khan established the nuclear research Laboratory at Kahuta, where a large number of Pakistani scientists are engaged in research work, in the field of nuclear Physics
• Different systems of units

  • MKS system (meter, Kg, second system)
  • CGS system (cm, gm, second system)
  • FPS system (ft, pound, second system)
• MKS System


  The fundamental units of length, mass and time are meter, kilogram and second respectively
• CGS System


  The fundamental units of length, mass and time are centimeter, gram and second
• FPS System


  The unit of force, length and time are pound, foot and second. The unit of mass is a derived unit
• SI Units


  Derived from the earlier MKS system. Introduced in 1960 and now used worldwide. Comprise seven basic units: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), candela (cd)
• Derived Units


  Units of other physical quantities derived from the fundamental units
• Dimensions


  Represent the physical nature of a quantity, expressed as a combination of the dimensions of fundamental quantities (length, mass, time)
• Positive x, y and z axes


  Denoted by i, j and k respectively
• Finding the magnitude of a resultant vector in a three dimensional rectangular co-ordinate system

  1. Consider a vector "A" with its initial points placed at the origin

  2. Find the rectangular components of the vector 'A' along positive x, y, & z axes as "Ax", 'Ay' & 'Az' respectively

  3. Add the rectangular components such as Ax, Ay and Az to get the original vector A

  4. The magnitude of the resultant vector A is given by A = √(Ax)² + (Ay)² + (Az)²
• Free vector


  A vector which can be displaced parallel to itself & applied at any point
• Position vector


  A vector which determines the position of a point relative to the fixed point
• Null vector


  If two vectors are identical in magnitude and opposite in direction, then the difference vector is called Null or ZERO vectors
• Commutative law of vector addition

  A + B = B + A
• Associative law of vector addition

  (A + B) + C = A + (B + C)
• Resolution of vector


  The process of splitting a vector into its components
• Addition of vectors by rectangular components method


  1. Resolve the vectors into their x and y components

  2. Add the x components to get the x component of the resultant

  3. Add the y components to get the y component of the resultant

  4. The magnitude of the resultant is √(Ax² + Ay²)
• Scalar product or dot product

  The product of magnitudes of two vectors and the cosine of the angle between them