Chapters :
  • Physics Properties of Matter – 02

Physics Properties of Matter – 02


 The French Scientist Blaise Pascal observed that the pressure in a fluid attest is the same at all points if they are at the same height. Distributed uniformly throughout. We can say whenever external pressure is applied on any part of a fluid contained in a vessel, it is transmitted undiminished and equally in all directions. This is the Pascal’s law for transmission of fluid pressure and has many applications in daily life. A number of devices such as hydraulic lift and hydraulic brakes are based on the Pascal’s law.  The flow of the fluid is said to be steady if at any given point, the velocity of each passing fluid particle remains constant in time. The path taken by a fluid particle under a steady flow is a streamline.

 BERNOULLI’S PRINCIPLE states when a fluid flows from one place to another without friction, its total energy (Kinetic + Potential + Pressure) remains constant.  You must have noticed that, oil and water do not mix; water wets you and me but not ducks; mercury does not wet glass but water sticks to it, oil rises up a cotton wick, in spite of gravity.  Sap and water rise up to the top of the leaves of the tree, hairs of a paint brush do not cling together when dry and even when dipped in water but form a fine tip when taken out of it. All these and many more such experiences are related with the free surfaces of liquids. As liquids have no definite shape but have a definite volume, they acquire a free surface when poured in a container. 

These surfaces possess some additional energy. This phenomenon is known AS SURFACE TENSION and it is concerned with only liquid as gases do not have free surfaces. Mathematically, surface tension is defined as the force acting per unit length of an imaginary line drawn on  the free surface of the liquid. The surface tension is expressed in NEWTON/METER.  
  • Most of the fluids are not ideal ones and offer some resistance to motion. This resistance to fluid motion is like an internal friction analogous to friction when a solid moves on a surface. It is called viscosity.
  • Mechanical waves require a material medium to travel (air, water, ropes). 
  • Transverse waves cause the medium to move perpendicular to the direction of the wave.
  • Longitudinal waves cause the medium to move parallel to the direction of the wave.
  • Surface waves are both transverse waves and longitudinal waves mixed in one medium.
  • Electromagnetic waves do not require a medium to travel (light, radio).  
    • Matter waves are produced by electrons and particles.
    • A point of maximum positive displacement in a wave, is called crest, and a point of maximum negative displacement is called TROUGH.
    • Measuring Waves: Any point on a transverse wave moves up and down in a repeating pattern. The shortest time that a point takes to return to the initial position (one vibration) is called period, T.
    • The number of vibrations per second is called frequency and is measured in hertz (Hz). Herat’s the equation for frequency: f = 1 / T
    • The shortest distance between peaks, the highest points, and troughs, the lowest points, is the wavelength,
    • By knowing the frequency of a wave and its wavelength, we can find its speed. Here is the equation for the velocity of a wave:
     However, the velocity of a wave is only affected by the properties of the medium. It is not possible to increase the speed of a wave by increasing its wavelength. By doing this, the number of vibrations per second decreases and therefore the velocity remains the same.  
    • The amplitude of a wave is the distance from a crest to where the wave is at equilibrium. The amplitude is used to measure the energy transferred by the wave. The bigger the distance, the greater the energy transferred.
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