Science questions in on sentence. [1 M]

Friction comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other. In sliding, the time given for interlocking is very small. Hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Because of this reason, sliding friction is less than static friction.

The cars, aeroplanes and rockets are streamlined so as to reduce the fluid friction. The air drag obstructs the vehicle to move forward and the fuel is consumed mainly for opposing this opposite frictional force. Therefore, the objects are given special shape called streamline shape, which itself cuts the air friction.

Force of friction arises because of the interlocking of irregularities of the two surfaces in contact. When a heavy object is placed on the floor, the interlocking of irregularities on the surfaces of box and floor becomes strong. This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus, to push the heavier box, Seema has to apply a greater force than Iqbal who has to push a lighter box. Concept insight: It is difficult to push a heavier object because friction increases with the weight of object. In case of a heavier object, interlocking becomes stronger.

Force of friction is desirable in many cases for example:
Stopping of vehicles: If there were no friction then we cannot stop our vehicles and the vehicles keeps on going and never stop but there is friction which helps us to stop our vehicles because it opposes motion always.
Writing: When we write on paper or blackboard then the pencil lead gets dragged on the paper due to friction and gets deposited on the sight where we move it, if there were no friction then there would be no writing on paper with pencil.
Walking on ground: When we walk on the ground it is due to friction which gives us forward reaction force due to which we are able to walk and if there were no friction then we were not able to walk..
Picking of objects: When we pick objects this is only due to force of friction because gravity is always acting on objects and if we pick an object it’s net force should be zero in order it to not to move.

When the body is in stationary state or is at rest, the frictional forces acting on the body is known as static frictional forces. But when the object is pushed and it moves, the friction that comes into action is sliding friction. The static friction is greater than sliding friction because more force is required to remove the object from rest state into dynamic state. Once the object comes into motion, it is easier to keep the object moving by applying comparatively lesser force.

The friction depends on the roughness as well as smoothness of the surface. If the surface is rough, then the surfaces in contact have more interlockings and the thus the friction is more. Thus, the object is not able to move easily due to more friction. If the surface is smooth, then the surfaces in contact have very less interlockings and the thus the friction is less. Thus, the object is able to move easily due to less friction.

When no person is sitting on the mat, then the mat and floor are not pressed together. Thus, there is no friction. But, when a person is sitting on the mat. Then due to the weight of the person, the mat and floor are pressed together harder, increasing the friction too much. Thus, then it is very difficult to drag the person.