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10. (C) Drag The frictional force exerted by a fluid is called drag.
Drag is a kind of frictional force exerted by fluid which opposes the motion of an object through that fluid. Drag force acts in direction opposite to the direction of motion of the object.
9. (A) Increases the friction with road Tyres are made corrugated and rough in order to increase the friction between tyres and the surface of the road.
8. The glaze paper or a wax paper has a smooth nature and therefore less friction and that is why it is difficult to write on it.
7. (D) All of these Friction comes into play when two irregular surfaces come in contact. The continuous rubbing of these surfaces together causes it to gradually wear out. Also, much of the applied force or energy is wasted in overcoming the force of friction. Hence, it is considered as evil, but it is necessary too.
Disadvantages of Friction
• Friction causes moving objects to stop or slow down.
• Friction produces heat causing wastage of energy in machines.
• Friction causes wear and tear of moving parts of machinery, soles of shoes, etc.
2. (C) Both A & B The interlocking of irregularities of the two surfaces opposes the motion of one object over the other and give rise to force of friction. Friction is caused by the interlocking of irregularities in the surface of two objects which are in contact with each other. Friction is a force that resists the relative motion between two objects or materials. The causes of this resistive force are molecular adhesion, surface roughness, and deformations. Adhesion is the molecular force resulting when two materials are brought into close contact with each other.
3. (B) Limiting friction The maximum friction that can be generated between two static surfaces in contact with each other. Once a force applied to the two surfaces exceeds the limiting friction, motion will occur. For two dry surfaces, the limiting friction is a product of the normal reaction force and the coefficient of limiting friction.
We define limiting friction as the friction which is exerted when equilibrium is on the point of being broken by one body sliding on another.
Hence, the maximum force of friction when the body is just beginning to move is known as the limiting friction.