NCERT 8th Class CBSE Science: Friction

Friction 8th Science – Question: Discuss the harms of friction.

Answer: Following are the harms of friction:

1. It results in wear and tear of shoes and tyres, machine parts, clothes, etc. It causes monetary loss.
2. Heat is generated by friction, which results in wastage of energy. Moreover, a significant amount of energy is wasted in overcoming friction.

Question: Discuss the benefits of friction.

Answer: Benefits of friction are as follows:

1. It is not possible to even walk on the road; in the absence of friction. Walking on ice is almost impossible because of lack of friction.
2. Friction is necessary to keep a ladder against a wall. The ladder will not find grip against the wall in the absence of friction.
3. It is very difficult to drive on a wet road because of less friction. A thin film of water is made over the surface of road. This thin film of water greatly reduces friction. Due to this, the driver finds it difficult to control the vehicle while driving on a wet road.

Friction 8th Science – Question: Discuss different types of friction.

Answer: Following are the three types of friction:

1. Static Friction: The minimum amount of force that is required to overcome the force of friction is called static friction. In other words, the minimum force that is required to make an object moving is called static friction.
2. Sliding Friction: Once an object starts moving on a surface, some force is required to keep the object moving. The minimum force that is required to keep a moving object in motion at a constant speed is called sliding friction. Sliding friction is always less than static friction. Due to this, it is easier to push a moving box compared to pushing a static box.
3. Rolling Friction: When an object rolls over a surface, the friction created is called rolling friction. Rolling friction is less than sliding friction.

Question: Boats and aeroplane are made in streamlined shape. Why?

Answer: A shape which is wide in middle and tapered at ends is called a streamlined shape. Such a shape reduces drag or fluid friction. Hence, a streamlined body can easily move through a fluid. Birds and fish are naturally endowed with streamlined body. Boats and airplanes are also made streamlined so that they can easily move through air or water.

Question: Why is it difficult to write on a glass surface?

Answer: Glass surface is so smooth that it does not provide friction to the tip of the pen. Hence, it is difficult to write on a glass surface.

Question: How does sand paper help in increasing friction?

Answer: A smooth surface can be made rough with the help of sandpaper. There are more irregularities on a rough surface than on a smooth surface. Thus, sand paper helps in increasing friction; by increasing the roughness of a surface.

Question: Why is it difficult to drive on a wet road?

Answer: It is very difficult to drive on a wet road because of less friction. A thin film of water is made over the surface of road. This thin film of water greatly reduces friction. Due to this, the driver finds it difficult to control the vehicle while driving on a wet road.

Question: It is easier to open a bottle cap by gripping it with a towel. Why?

Answer: Rough surface of towel helps in increasing friction, and thus provides a better grip. The towel, thus, makes it easier to open the bottle cap.