Chapter 2 : Fundamental Definitions

Topics covered in this snack-sized chapter:



Fundamental Quantities used in the field of Mechanics arrow_upward



Body

  • A body is a matter which occupies a finite space.
  • A body is made up of atoms and molecules arranged in a complex but continuous manner. 
  • A body may be rigid or non-rigid (deformable).

    • Rigid Body

  • A Rigid body is an idealization of a solid body which has a perfectly definite and unchanging shape and size.
  • Rigid body can be represented as collection of particles.

    • Deformable Body

  • A body is considered deformable when the changes in distance between any two of its points cannot be neglected.

    • Particle

  • A Particle is an object whose size and shape can be ignored when studying its motion.
  • Only the position of the mass center of the particle needs to be considered.

    • Space

  • Geometric region extends without limit in all direction in which Physical events of interest in mechanics occurs.
  • Points in space can be determined relative to some reference system.
  • The measure used to describe the size of physical system is known as Length.

    • Time

  • Time can be defined as the interval between two events.
  • Measurement of interval is made by making comparison with some reproducible event such as the time required for the earth to orbit the sun.

    • Matter

  • Any substance that occupies space is called Matter.
  • A body is matter bounded by closed surface.

    • Mass

  • It is a measure of the inertia of a body, which is its resistance to a change of velocity.

    • Force

  • Force is any influence that causes an object to undergo
    • A change in speed,
    • A change in direction, or
    • A change in shape
  • Force can also be described by intuitive concepts such as a push or pull.
  • A force has both magnitude and direction.
  • Force is a vector quantity.

    • Push or Pull on an object




    Vector Quantity

  • A Vector is defined to be a directed line segment.
  • A vector quantity has both magnitude and direction.
    • Examples: Acceleration, velocity, force, displacement, etc.
  • Vectors can be depicted graphically in two or three dimensions.

    • Scalar Quantity

  • A Scalar quantity has only magnitude and no direction.
    • Examples: Speed, time and distance.

    Newton’s Mechanics arrow_upward


  • Newton's laws of motion are three Physical Laws that form the basis for mechanics.
    • They describe the relationship between the forces acting on a body and its motion due to those forces.


    Newton’s First Law

  • Newton’s first law of motion states that an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted on by an outside force. This is also called Inertia.

    • Newton’s Second Law

  • When a particle is acted on by an unbalanced force, the particle will be accelerated in the direction of the force

    • then magnitude of the acceleration will be directly proportional to the force and inversely proportional to the mass of the particle.

    Where

    •  is the external force acting on the body
    • is the mass of the body
    • is the acceleration of the particle in the direction of the force

    Newton’s Third Law

  • For every action there is an equal and opposite reaction.
  • The forces of action  and reaction  between contacting bodies are equal in magnitude and opposite in direction.
  • This is sometimes called the Law of Action and Reaction.


    • Example:

    • In the above figure enclosed air particles push balloon wall outwards and balloon wall pushes enclosed air particle inwards.

    Mass & Weight

  • Mass and Weight are different in physics
  • as well as mechanics.
    • For example, our mass does not change when we go to the Moon, but our weight does.
    • Mass shows the quantity, and weight shows the size of gravity.
  • If we know our mass, we can easily find out our weight through-

    •    Where

    •  is weight in Newton  
    •  is mass in  
    •  is the acceleration of gravity in

    Example:

  • If your mass is 50 kg on Earth, than weight is
  • Weight is measured by Newton

    • Units of Measurement arrow_upward



    Quantity

    Unit

    Length

    Meter

    Mass

    Kilogram

    Time

    Second

    Acceleration

    Meter/second2

    Force

    Newton

    Velocity

    Meter/second

    Pressure/Stress

    Pascal

    Density

    Kilogram/meter3

    Work, Energy

    Joule

    Spring constant

    Newton/meter

    Moment of force

    Newton-meter

    Moment of inertia, mass

    Kilogram-meter2

    Area

    Meter2

    Frequency

    Hertz



    Unit

    SI symbol

    Meter

    m

    Kilogram

    kg

    Second

    s

    Meter/second2

    m/s2

    Newton

    N

    Meter/second

    m/s

    Pascal

    pa

    Kilogram/meter3

    kg/m3

    Joule

    J

    Newton/meter

    N/m

    Newton-meter

    N-m

    Kilogram-meter2

    kg – m2

    Meter2

    m2

    Hertz

    Hz




    Thank You from Kimavi arrow_upward


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