Physics Education

Introduction - we always see that our sandal is worn out, our bicycle tires are worn. This is because of frictions. Similar friction occurs in liquid’s different layers. In case of liquid; this friction is termed as viscosity. Concept of viscosity Consider two plates, Plate-1 is fixed & plate-2 is free to move. If some oil is present between two plates; then plate-2 moves with certain velocity. Now if oil is replaced by "honey" then greater force is required to move plate-2. This shows that honey is more viscous than oil. Now let us consider Layer L 1 , L 2 & L 3 moving with velocities V-dv, V & V+dv respectively. Layer L 3 , forces layer L 2 to move with its velocity at the same time layer L 1 , pulls L2 in backward direction. As a result of which there is the opposition to relative motion between them. Hence friction is created between two liquid layers; which is called viscous force. Viscous force - The force that opposes relative motion between two ...

Capillary action - It describes the ability of a liquid to flow against gravity in a narrow space such as a thin tube. Capillarity - The phenomenon of rise & fall of liquid in a Heron capillary on account of surface tension is called capillarity. Examples of capillary action - Rise of oil in lamp is due to capillarity. Moisture rises in plant by capillarity action. A blotting paper absorbs ink by capillary action. Moisture from the foundation of the house rises in the wall due to capillary action. The action of a towel in soaking up moisture from the body is due to capillary action of cotton in towel. Shape of meniscus (top surface in capillary tube) –   In case of water Consider water molecule "P" on the surface near wall. It experience two forces one is force of adhesion (R A ) & the other is force of cohesion (R C ). In order to balance these two forces the resultant force (R) is in such direction which tends liquid surface in concave shape.   In ca...