Friction Questions and Answers:Solved Important Questions Class 11 Physics

Ans. To increase friction.

Ans. It remains same.

Ans. Coefficient of friction between road and synthetic rubber is large.

Ans. In case of normal plane surface the coefficient of friction is less than unity, but when the surfaces are so irregular that sharp minute projection and cavities exist on the surface. The coefficient friction may exceed

Ans. $\theta=\tan ^{-1}(\mu)=\tan ^{-1}(1 / \sqrt{3})=30^{\circ}$ where $\theta=$ friction angle $\mu=$ coefficient of friction.

Ans. Sand is thrown on snow to increase the force of friction, so that tyres of the vehicles may not slip over the snow.

Ans. As the wheel rolls forward the part of the wheel in contact of the road slides backward hence the force of friction acts in the forward direction along the tangent to the surface of the road and the part of the wheel in contact.

Ans. The lubricant forms a thin layer between the two surface in contact. Thus sliding friction is replaced by liquid friction which is much smaller.

Ans. Because ball bearing convert sliding friction into rolling friction.

Ans. Normally friction decreases when smoothness of surface increases however, when surface in contact are made too smooth then binding force of adhesion increase which increases friction. This phenomena is called cold welding.

Ans. The weight of the vehicle and its occupants cause some flattening of the part of the wheel in contact with the ground and make some hollow space in the ground hence work is done in lifting the wheel Less work would be done if the rubber wheels are hard that is fully inflated. When they will be flattened less, less work would require less consumption of fuel per unit distance covered.

Ans. Friction is called a necessary evil. It is necessary because we cannot do without it. At the same time it is an evil because it involves unnecessary wastage of energy. The following facts make the point clear Friction is a necessity

Ans. There are five laws of friction. (1)The direction of the force of limiting friction is always opposite to the direction in which the motion takes place or tend to take place. (2) The force of friction acts tangentially along the surface of contact of two bodies. (3) The magnitude of the limiting force of friction (F) is directly proportional to the normal reaction (R) between the two surface. i.e. F µ R. (4) Force of limiting friction is independent of the area of the surface of contact of two bodies as long as normal reaction is constant. (5) The force of limiting friction depends on the nature of the surfaces in contact.