 # Physics Practical Class 11 - To study the relationship between force of limiting friction and normal reaction and to find the coefficient of friction between a block and a horizontal surface. Viva Questions with Answers

1) The coefficient of static friction is more than the coefficient of kinetic friction. Is it true or false?

The above statement is true because between two surfaces, the normal reaction is directly proportional to the value of kinetic energy. Thus, the coefficient of static friction is more than the coefficient of kinetic friction.

2) How can one reduce the friction due to air?

By streamlining the shape of the body moving through the air, the friction due to air can be significantly reduced, for instance, the streamlined shapes of jets and fins of aeroplanes.

3) How many types of kinetic friction are there?

There are two types of kinetic friction; rolling friction and sliding friction. Sliding friction is more than rolling friction, and due to this reason, rolling a body is always easier as compared to sliding it.

4) What is sliding friction?

To keep a surface sliding along another surface, the force required is known as sliding friction, which is also identified as moving friction or kinetic friction.

5) Give some examples of sliding friction.

A car is sliding on ice.

A child is sliding through a slide in a park.

A mat is sliding against a table.

A washing machine is being pushed along with the floor.

6) What is limiting friction?

When two static surfaces come in contact with each other, the friction generated between them is known as limiting friction. It is the product of the coefficient of limiting friction and the normal force.

7) Give some examples of limiting the force of friction.

Moving a car on a cliff.

Moving an object on the ground.

8) Why are brake surfaces kept flat?

When the brakes are applied, they get pushed from the surface of the brake rotor and the hydraulic pistons. Since brakes are always applied from both sides, which produces the friction and the vehicle stops, due to this reason, the surface of brakes should be kept flat to get maximum friction.

9) Define the coefficient of friction.

At the surface of contact between two bodies, there exists a constant ratio; this ratio is known as the coefficient of friction. It is defined as the ratio of frictional force to the normal reaction on a surface.

10) After rains, the roads become slippery; why?

After rains, a thin layer of rainwater covers the surface of the road, and due to this, friction between the feet and the road reduces. So, the roads become slippery after rains.