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Friction
Friction
TYPES OF FRICTION
CONTACT FORCE AND NORMAL REACTION
When two bodies are kept in contact, Electro magnetic forces act between charged particles at the surfaces of the bodies. As a result each body exerts a force on the other body. The resultant molecular force exerted by the surface of one body on the contacting surface of other body is called contact force. Contact forces make an action -reaction pair.
However the direction of a contact force may not be perpendicular to contact surface. It can be resolved into two components. One, parallel to contact surface is called friction and the other, perpendicular to contact surface is called normal reaction force.From the above discussion we can conclude that normal reaction and friction are Electro- magnetic in nature. Normal reaction is normal to the contact surface and friction is parallel to contact surface.
Normal reaction is the normal component of contact force acting on a body placed rigid surface perpendicular to the plane of contact.
Normal reaction depends only on the nature of the contact. It does not depend on the area of contact. Even in the event of the motion of the body on the surface this force remains unaltered.
Consider a body of mass 'm' lying on a horizontal surface. The weight of the body acts vertically down on the surface. The surface exerts a reaction "N" of same magnitude on the body in a direction vertically up, then N = mg
When a body of mass "m" is on an inclined plane of inclination "\(\theta\)", the weight of the body "mg" acts vertically downwards, and a component mg cos\(\theta\) perpendicular to the inclined plane is exerting a contact pressure, then N = mg Cos \(\theta\) -
Friction
FRICTION:
According to Newton's first law of motion, a body continues in its own state of rest or state of uniform motion unless it is compelled by an external force to change that state.
Let us see some examples,
(a) If a body is placed on horizontal surface and a small force is applied on it, then it may not move. It is clear that some or other force must have come into play to keep the body in equilibrium
(b) If the force on the above body is sufficiently large then it is set into motion. If the application of force is ceased then the body moves through some distance on the surface and comes to hault. Here also some force must have come into play to stop the motion of body on the surface.
(c) If we stop peddling our bicycle, then it comes to rest after traveling certain distance.
In all these examples, the force that is impending motion or that is opposing relative motion and is called friction or frictional force
Friction may be defined as the opposing force which comes into play tangentially between two surfaces so as to destroy the relative motion between them.
Friction is the contact force along common tangent to the contacting the surfaces to destroy the relative motion between them.
Friction non conservative force. -
Friction
CAUSES OF FRICTION:
1.A surface though appears smooth by visual inspection or by touch, but when viewed under a powerful microscope, it consists of a large number of surface irregularities.
2.When two bodies are placed one above the other, these surface irregularities interlock together and oppose any attempt to bring a relative motion between the bodies.
3. At the actual points of contact a sort of "welding" takes place due to intermolecular forces.
4.When a sufficiently large force is applied, these irregularities will be sheared off and breaking of welded joints takes place and the body starts sliding on the surface.
5. Friction is due also to cohesive or adhesive force among molecules at close proximity.
6. Friction is regarded as electromagnetic force -
Friction
ADVANTAGES AND DISADVANTAGES OF FRICTION:
A) ADVANTAGES OF FRICTION :
The advantage of friction can be understood if we imagine the situation when friction is absent. The surfaces in contact will slip on each other without opposition in the absence of friction. This may produce undersirable and dangerous motion. Friction is very much necessary to produce a controlled motion. The following are a few examples.
1. Safe walking on the floor is possible because of friction between the floor and the feet.
2. Nails and screws are held in the walls or wooden surfaces due to friction.
3. Friction helps the fingers to hold a drinking water tumbler or a pen.
4. Vehicles move on the roads without slipping due to friction and they can be stopped due to friction.
5. The mechanical power transmission of belt- drive is possible due to friction. -
Friction
B) DISADVANTAGES OF FRICTION:
1.Friction is disadvantageous because it results in loss of mechanical energy and hence produces many undersirable effects. Few examples are given below.
Friction results in the large amount of power loss in engines and hence brings down their efficiency.
2. The wear and tear of the machines increases due to friction reducing their life.
3. Friction causes unnecessary heating of the parts of the machinery which may alter their operating conditions. -
Friction
METHODS OF REDUCING FRICTION
1. Polishing :
Friction between two surface of contact can be reduced by polishing the surfaces to some extent. But if this polishing is carried beyond certain extent the molecules on the surfaces come so close that the intermolecular force opposes the relative motion and thus friction increases.
2. Using Lubricants:
A thin layer of an oil (or) a fluid is used between the surfaces in contact to reduce friction. A suitable lubricants is used based on the degree to which the friction should be reduced and the operating condition. Specially laminated organic oils, compressed air are generally used as lubricants. Lubricants help in preventing the surfaces in contact from getting overheated.
3. Using ball bearings:
The free wheels of vehicles like bicycles, two wheelers, motor cars, shafts of motors, dynamos etc., are provided with ball bearings to reduce friction by replacing sliding with rolling. This is because, friction while in rolling motion is less than friction while in sliding motion.
4.Streamlining:
Automobiles and aeroplan specially designed with curved surfaces, so that the air layers may get streamlined during the motion and hence reduce friction.
Note s: A thin cushion of air maintained between solid surfaces in relative motion is another effective way of reducing friction.