This force works against the movement of different layers within liquids or gases.
Viscosity: Viscosity is a characteristic of both liquids and gases. It refers to the resistance they show against the relative motion between different layers.
- 1. In liquids, viscosity is due to the cohesive force between their molecules.
- 2. In gases, viscosity arises from the diffusion of molecules between layers.
- 3. Gases have much lower viscosity compared to liquids, and solids have no viscosity.
- 4. For an ideal fluid, viscosity is zero.
- 5. Temperature affects viscosity: as it rises, the viscosity of liquids decreases while that of gases increases.
- 6. Viscosity is measured using the coefficient of viscosity, with its SI unit being the pascal second or decapoise (kg/ms). It's usually denoted by the symbol η.
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Terminal Velocity: When an object falls through a thick fluid like air or water, its speed initially increases but eventually levels off. This constant speed is called terminal velocity. At this point, the force of gravity pulling the object down is balanced by the combined forces of friction and buoyancy pushing up.
Streamline Flow: If a fluid flows smoothly and evenly, with all its particles moving at the same speed and following the same path, it's called streamline flow. Each particle travels in the path laid out by previous particles passing through that point.
Critical Velocity: This is the maximum speed at which fluid flow remains smooth and streamline. If the flow speed is below critical velocity, it's streamline; if it's above, it becomes turbulent.
Bernoulli's Theorem: According to this principle, in a smooth flow of an ideal fluid (one that's non-viscous and incompressible), the total energy per unit volume stays constant. This total energy includes pressure energy, potential energy, and kinetic energy. Venturimeter, a device used to measure fluid flow rate, relies on Bernoulli's theorem.
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