What is friction –
If another solid object is placed on a fixed solid object in such a way that both the flat surfaces touch each other, then in this case a force has to be applied to move the second object on the first object. The value of this force is When less than a limit, the second object cannot slide on the first object. This opposing force is called friction.
Friction is a force that opposes relative tangential motion between two surfaces. The value of frictional force depends on the normal force between the two planes.
There are two types of friction: static friction and kinetic friction. Static friction occurs in the direction parallel to the contact surface of two bodies, but kinetic friction does not depend on the direction of motion.
Cause of friction –
Generally, no surface is completely smooth, but it has ups and downs of very small magnitude. These can be seen only with a good microscope. Hence, when two such surfaces touch each other, the depressions of one surface get trapped in the depressions of the other surface. In this condition, on applying force to slide one surface on another surface, the texture of the surface gets distorted. Accordingly, due to the elasticity of the material, stress acts in the opposite direction to the applied force, which is called the force of friction.
Uses of friction –
Friction has a very important place in our daily life. The movement of every vehicle moving on the surface of the earth is possible only due to the force of friction between the surface and the base of the vehicle. Therefore, friction is both a hindrance and an enabler. Friction also plays a major role in the behavior of bearings and lubricants.
The magnitude of friction –
To displace a solid body on a solid surface, a force parallel to the surface of contact has to be applied. If the applied force is less than a certain magnitude (extreme frictional force), then the body is not displaced and if it is greater, it is displaced with a certain velocity. This is due to the friction between the touching surfaces, This means that there is a force acting parallel to the surface of contact on a solid body in the direction opposite to the applied force, which is called the force of friction. The force of friction is due to the roughness of the surfaces.
Before displacement (when the body is at rest) the frictional force is equal to the applied force, which is called static friction. The force used for displacement must be of at least such a magnitude that the deformation exceeds the elastic limit. The magnitude of this minimum force required for displacement is called the ultimate frictional force.
The ultimate frictional force (Fa) and the normal pressure (P) between the two surfaces have the following relation:
Fa = b1 P
While (b1) is called the static friction constant. Its value can be determined by placing the body on the surface and finding the minimum inclination angle (q) of the surface at which the body starts sliding. This angle is called the angle of friction. The tangent of the angle of friction is equal in magnitude to the constant of static friction, i.e.
B1 = tan q
Even during motion, the force of friction acts on the body. Its magnitude mainly depends on the type of displacement. A solid body can be displaced only by sliding or rolling it on a solid surface; Therefore, according to these two types of displacement, there are two types of kinetic friction.
1 – sliding friction
2- rolling friction For both types of motion, the magnitude of frictional force is expressed by the following formula:
Fb = bc x P
While (Fb) is the force of friction, (P) is the pressure normal to the surface, and (bc) is the constant of kinetic friction, the value of which depends on both surfaces. For the small relative motion of surfaces, the value of Kg does not depend on the magnitude of the motion. But when the magnitude of speed exceeds the critical velocity, then the value of Kg increases with the increase of velocity. The value of Kg is different for twisting and rolling and sliding motions.
Friction coefficient –
The static friction coefficient is the relative motion tendency of two objects but no friction coefficient when moving relative to each other, usually denoted by the symbol μ0. Friction coefficient = friction force /hh normal force
Μ = F / η
Where μ = friction coefficient
F = force of friction
Η = normal force
The friction coefficient of some materials –
static friction | | between (substance) dry | clean lubricated |
Aluminium | Steel | 0.61 | |
copper | Steel | 0.53 | |
Brass | Steel | 0.51 | |
Cast | Iron Copper | 1.05 | |
Cast | iron Zinc | 0.85 | |
Concrete | Rubber | 1.0 | 0.30 (wet) |
concrete | timber | 0.62 | |
copper | glass | 0.68 | |
glass | glass | 0.94 | |
metal | wood | 0.2–0.6 | 0.2 (wet) |
Polyethene | Steel | 0.2 | 0.2 |
Steel | Steel | 0.80 | 0.16 |
Steel | (Teflon) | 0.04 | 0.04 |
PTFE | PTFE | 0.04 | 0.04 |
Wood | Wood | 0.25–0.5 | 0.2 |
By Chanchal Sailani | January 17, 2023, | Editor at Gurugrah_Blogs.
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