# General Awareness

General Awareness -Physics -Friction

1-The force which opposes the relative motion of two surfaces of bodies in contact is called frictional force.

2-Frictional force acts in the opposite direction of the applied force.

3-Frictional force is the force that slows down the moving bodies.

4-Frictional force occurs due to interlocking of irregularities in the surfaces.

5-Frictional force depends on the nature of surfaces in contact and on the roughness of areas of contact.

6-Frictional force can be increased or decreased by making the surfaces in contact rough or smooth.

7-Friction is sometimes undesirable.

8-Frictional force is independent of area of contact.

9-Friction is minimised by using lubricants, polishing,streamlining and ball bearings.

10-Friction is classified into three types.They are -a) Static friction. b) Kinetic friction or sliding friction . c) Rolling friction.

11-The friction which comes into play when surfaces of the objects are at rest relative to each other is called Static friction.

12-The friction which comes into play when the surface of one object moves relative to the surface of another object is called sliding friction.

13-The friction which comes into play when the object roll on a surface is called rolling friction.

14-Frictional force is independent of weight but depends on normal force between surfaces of contact where friction exists.

15-Frictional force produces heat.

16-Friction in liquids and gases is known as drag.

17- Frictional force is used in following situations.

a- When we walk on the road.

b-When vehicles moving on the road.

c-Lighting of matchstick by a matchbox.

d-To stop the vehicles.

18-Lubricants are substances introduced to reduce friction between moving surfaces.

19-Ball bearings are spherical balls which are used in fans, cycle pedals etc,which converts static friction to rolling friction, the rolling friction is less.So ball bearings are used to reduce the friction.

20-Fluid friction- The frictional forces between the liquid layers or between the liquid surfaces that is in contact with glass surface. Fluid friction is also viscous force. We can observe fluid friction when we travel in a boat.