Friction

Electromagnetic Waves

Electromagnetic Waves

Text Box: INTRODUCTION DO YOU KNOW WHAT FRICTION IS? Friction is the force resisting the relative motion of two surfaces in contact or a surface in contact with a fluid (e.g. air on an aircraft or water in a pipe). It is not a fundamental force, as it is derived from electromagnetic forces between atoms and electrons, and so cannot be calculated from first principles, but instead must be found empirically. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects is often referred to as dry friction or sliding friction and between a solid and a gas or liquid as fluid friction. Both of these types of friction are called kinetic friction. Contrary to many popular explanations, sliding friction is caused not by surface roughness but by chemical bonding between the surfaces. Surface roughness and contact area, however, do affect sliding friction for micro- and nano-scale objects where surface area forces dominate inertial forces. Internal friction is the motion-resisting force between the surfaces of the particles making up the substance. Friction should not be confused with traction. Surface area does not affect friction significantly because as contact area increases, force per unit area decreases. However, in traction surface area is essential. Simple example of friction is shown by a figure below TYPES OF FRICTION 1. Static friction 2. Rolling friction 3. Kinetic friction STATIC FRICTION Static friction is a force between two objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction, typically denoted as μs, is usually higher than the coefficient of kinetic friction. The initial force to get an object moving is often dominated by static friction. Another important example of static friction is the force that prevents a car wheel from slipping as it rolls on the ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction. The maximum value of static friction, when motion is impending, is sometimes referred to as limiting friction, although this term is not used universally. The value is given by the product of the normal force and coefficient of static friction. PICTURES GIVING EXAMPLES OF STATIC FRICTION ROLLING FRICTION Rolling friction hinders the motion of an object rolling along a surface. Rolling friction slows down a ball rolling on a basketball court or softball field, and it slows down the motion of a tire rolling along the ground. Another force must be present to keep an object rolling. For example, a pedaling bicyclist provides the force necessary to the keep a bike in motion. Rolling friction depends on the coefficient of rolling friction between the two materials (µr) and the normal force (N) of the object. The coefficient of rolling friction is usually about t that of sliding friction. Wheels and other round objects will roll along the ground much more easily than they will slide along. PICTURES GIVING EXAMPLES OF ROLLING FRICTION KINETIC FRICTION Kinetic friction is the type of friction that an object is subject to after it is in motion. Kinetic friction is typically lower than static friction. The force of kinetic friction can be calculated if one knows the coefficient of kinetic friction and the normal force on the object. It can be calculated using the equation Ff=muf times Fn, where Ff is the force of kinetic friction, μf is the coefficient of kinetic friction, and Fn is the normal force on the object. PICTURES SHOWING THE EXAMPLES OF KINETIC FRICTION ADVANTAGES AND DISADVANTAGES OF FRICTION ADVANTAGES OF FRICTION
Friction plays a vital role in our daily life. Without friction we are handicap.
1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it becomes difficult to walk due to low friction of ice.
2. We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
3. A horse can not pull a cart unless friction furnishes him a secure Foothold.
DISADVANTAGES OF FRICTION Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:
1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
2. Due to friction we have to exert more power in machines.
3. It opposes the motion.
4. Due to friction, noise is also produced in machines.
5. Due to friction, engines of automobiles consume more fuel which is a money loss.
METHODS OF REDUCING FRICTION There are a number of methods to reduce friction in which some are discussed here. USE OF LUBRICANTS The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity. USE OF GREASE Proper greasing between the sliding parts of machine reduces the friction. USE OF BALL BEARING In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.
DESIGN MODIFICATION Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.