On a rainy day, it is difficult to drive a car or bus at high speed because the value of coefficient of friction is lowered on wetting the surface. and hence car or bus may not be stopped at a desired point.

Since on ice there is no frictional force, the foot slips when he tries to exert force on ice to make himself move forward.

If we imagine ideally smooth surface kept in contact, the frictional force acting between them is zero because there are no irregularities in the surface to interlock the other surface. Interlocking is the reason behind friction. Its absence means there will be no friction between these surfaces to resist the motion whenever they move relative to each other.

Fluid friction occurs when a solid object travels through a liquid or gas. Aeroplanes are streamlined to reduce the fluid friction.

Sand is dusted to the railway tracks to reduce the smoothness of the track. This results in increase of friction.

A good lubricant generally possesses the following characteristics:

1) High boiling point and low freezing point (in order to stay liquid within a wide range of temperature)

2) High viscosity index

3) Thermal stability

4) Hydraulic stability

5) Corrosion prevention

6) High resistance to oxidation.

Now, only liquids can have all the above properties.

Limiting friction is 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 occurs. 

A  good lubricant should be highly viscous  because due to viscosity the lubricant will stick between the solids and it overcomes the friction between the two surfaces that are in contact. 

Due to the force of friction between the ball and table top, it  opposes the motion of the ball. And, gradually its speed keeps on decreasing and the ball finally stops.

The only path will have sufficient frictional force to walk easily, hence the answer is (d) gravel.

The given statement is true.

The air resistance or friction by air for the feather will be more due to its large surface area. So the coin will go fast and strike the ground.  

Lubricants reduce the roughness of a surface and make them smooth. 

Rough surface is uneven so it provides more resisitance to motion of a body hence the frictional force increases.

Lubrication always decreases friction between two surfaces. Hence putting oil will decrease friction.

Polishing and Lubrication are two methods to reduce the friction between contact surfaces. ex- We use powder on the carrom board to reduce the friction. 

Friction is caused due to relative motion between two different objects. It is a force between two surfaces that are sliding, or trying to slide, across each other. It always works in the direction opposite to the direction in which the object is moving, or trying to move.

The force of friction opposes the relative motion between the heavy box and rough surface.

Ball bearing are used in rotating machine parts to reduce rolling friction.

Friction is desirable in braking of a vehicle. As brakes are applied, friction between brake shoes and tyres opposes rotation of tyres and hence, forces it to stop.

Glass has comparatively a better polished and regular smooth surface. So it  has least friction. 

Lift is the upward acting force which is against gravity. Drag is the resistance force or friction force in fluid. The rolling friction is a resistive friction when a body rolls on a surface. The dynamic friction is the friction that must be overcome to maintain steady motion of one object relative to another because they remain in contact.

Friction always acts between two contact surfaces of bodies. Hence it is a contact force.

Powder is used to increase smoothness of the board. It fills the irregularities and makes the surface smoother. This decreases the friction to play well.

Friction is caused by the irregularities on the two surfaces in contact. Irregularities on the two surfaces lock into one another. When we attempt to move any surface, we have to apply a force to overcome interlocking. On rough surfaces, there are a larger number of irregularities. 

The table exerts a frictional force on the coin in the reverse direction and thus, the coin stops across the table. The force of friction always opposes the applied force.

Powder is a lubricant because it consist of fine particles and makes the surfaces smooth and hence it reduces the friction among surfaces.

Oil is the best and the most commonly used lubricant used for keeping machines running smoothly and to avoiding wear and tear of machines as it reduces the friction more effectively.

When we walk on road, the friction will occur between the soles of our shoes and road so that slipping can be prevented. Thus the road wears out the soles due to friction.