Friction in Solids and Liquids

Origin of Friction
Friction originates from the idea that no surface is perfectly smooth, and that a part of kinetic energy is lost due to moving on such a surface.

When two bodies are kept in contact with each other, they exert electromagnetic force on each other. The negative charges and positive charges align themselves close to each other, thus offering resistance to the relative motion between the objects.

Types of Friction
Static Friction : Friction acting on an object so as to keep it static.

Kinetic Friction : Friction acting on a moving object so as to reduce its velocity .The direction of Kinetic Frictional Force is in opposite direction to its motion.

Rolling Friction : Friction acting on Rolling objects.

Laws of Friction
F = usN

This is followed by all three kinds of frictions.

Fluid Pressure
The pressure exerted by a fluid on the walls of container or surface that supports it is called as Fluid Pressure.

P =hρg = ρgV

Pascal's Law
Pascal's Law states that the Pressure is the same at all points in a Fluid enclosed in a container.

Applications of Pascal's Law
 * 1) Hydraulic Lift
 * 2) Hydraulic Press
 * 3) Hydraulic Brakes

Hydrostatics
The study of Water Molecules at rest is called as Hydrostatics.

Buoyancy
Buoyancy is the property of a fluid to provide an upthrust to an object immersed in it. The upthrust is also called as Buoyant Force.

Archimedes Principle
The Archimedes Principle states that the amount of buoyant force applied on a body is equal to the weight of the fluid that is displaced by it.

Flow of Liquid
Flow of liquid can be streamlined or turbulent.

In streamlined flow, the layers of fluid smoothly flow over each other and do not mix up.

In turbulent flow, the layers of liquid randomly mix up with each other and flow.

R <= 2000 Streamline Flow

R > 2000   Turbulent Flow

Viscosity
(Poiseulle Equation excluded for JEE)

Viscosity is the resistance to flow of a fluid. It occurs between the layers of a fluid. It is similar t friction and both have a common origin.

Viscous Force = ηAv ; where η is co-efficient of Viscosity.

SI unit of Coefficient of viscosity is poiseulle.

1 Poise = 10 Poiseulle

Stoke's Law
Viscous Force = 6πηrv

Terminal Velocity
v = 2/9 [rg(ρ-σ)/η]

Bernoulli's Principle
(Theorem and Application for JEE)

The Sum of Pressure Energy, Kinetic Energy and Potential Energy of a Fluid is constant

Applications of Bernoulli's Theorem
 * 1) Aerodynamic Lift

Toricelli's Law
v = √2gh

Tips and Tricks

 * 1) For friction, draw the free body diagram and resolve the vectors . Mostly , the free body diagram is standard , so you can learn the resolved forces beforehand.