# NCERT Solutions Class 8 Science Chapter 12

## NCERT Solutions for Class 8 Science Chapter 12

Science is enthralling. Science is a method of learning what exists in the universe and how it functions today, functioned in the past, and will do so in the future. Scientists are inspired by the pleasure of uncovering or discovering something previously unknown. Science exists all around us. The fact that you can read this text and live simultaneously is Science.

Friction is the resistance that any item encounters when travelling across or through a surface or medium. NCERT Class 8 Science Chapter 12 is Friction. It teaches that in the absence of frictional force, an object’s movement would either not begin or, if already underway, would not come to a complete halt. The chapter discusses the numerous forms of friction we observe daily.

Extramarks NCERT solutions provide detailed and authentic answers to all the textbook questions. Through those, the students can understand, remember and retain answers to NCERT questions and thus, perform well in exams.

The experts have prepared Class 8 Science Chapter 12 Solution. Going through the NCERT Solutions of a chapter is essential for students to get better results in the examinations. Hence, Extramarks provides Class 8 Science Chapter 12 NCERT Solutions of the chapter Friction. These solutions not only help to learn the concepts but also to retain them.

Extramarks can be a one-stop solution for all students’ problems. Apart from NCERT Solutions for Class 8 Science Chapter 12- Friction, NCERT Solutions, Additional Questions, Sample Papers, Revision Notes, CBSE Previous year question papers, and a lot more can be found on the Extramarks website.

## Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 12

Making it easier for the students and listing below the key topics that are covered in NCERT Solutions for Class 8 Science Chapter 12:

 What is Friction? What causes friction? Factors affecting friction Types of Friction Friction- Both Friend and Enemy How do you increase and reduce friction? What is Drag Force?

Let us look at Extramarks in-depth information on each subtopic in NCERT Solutions for Class 8 Science Chapter 12- Friction.

### What is Friction?

A ball thrown on the floor moves all over. However, if no opposite force is exerted in the direction of motion, the ball should continue to roll as per Newton’s first law, but this does not happen. In place of it, the ball comes to a halt after a set distance, indicating that an opposite force is operating on it and causes it to stop. Friction is what we term this force as.

Extramarks’ NCERT Solutions for Class 8 Science Chapter 12 defines friction as the resistance provided by the surfaces in contact as they move past one another.

Relative Motion

A relative motion occurs when one thing moves in relation to another.

### What causes friction?

Due to uneven surfaces of the objects coming into contact, a frictional force is created. This frictional force interlocks micro-level irregularities between the two characters and ploughs harder surfaces into smoother surfaces. As a result, the frictional force is the opposite of the force of motion and causes a speed reduction, and eventually, the object stops its state of motion.

Surface Irregularities

• If zoomed in to a microscopic level, all surfaces have hills and valleys that interlock when they move or brush against one another.
• Surface irregularities or roughness refers to the unevenness of the surface.
• Surface imperfections are bigger on rough surfaces and smaller on smoother surfaces.

• When two surfaces come into contact, they begin to create bonds and adhere to one another. Adhesion is the term for this phenomenon.
• When we try to move things stacked on top of one another, we are breaking or overcoming adhesive forces.

Ploughing Effect

• When surfaces are soft or easily flexible, they distort when they come into touch with another item. For example, when a heavy object is put on a carpet, the distortion of the shape creates the appearance of a valley.
• Ploughing is the term for the action of surfaces sinking into one other.

Extramarks NCERT Solutions for Class 8 Science Chapter 12 explains friction causes in the above points. Refer to Extramarks for more details on such information.

### Factors affecting friction

Multiple factors affect Friction; Extramarks NCERT Solutions for Class 8 Science Chapter 12 states the following:

Nature of Surface in Contact

• Friction is determined by how strongly the two surfaces are forced together; as more surfaces come into contact, more bonds are created, and more bonds are broken, the friction increases.
• Friction is increased only when the usual response force (perfectly perpendicular) to the two surfaces is applied.

Calculating Frictional Force using a Spring balance

• We can discover the frictional forces that various materials resist using a spring balance.
• In comparison to stainless steel, sandpaper offers a greater reading.

Polishing surfaces in contact to change friction

• Surface polishing removes imperfections and hence smooths the surface.
• Friction is reduced.

Normal Reaction Force

• The typical reaction force is an applied force perpendicular to the surfaces in contact.
• The frictional force is increased.

### Types of Friction

Extramarks NCERT Solutions for Class 8 Science Chapter 12 explains different types of friction as follows:

Static Friction

It is the force of friction operating on a body when it is at rest. This force is always equal to and opposing the object’s applied force. Limiting friction is the force that acts when the body is just at the point of slipping on the surface.

Sliding Friction

The force that resists sliding motion between two surfaces in touch, is called friction. The sliding  friction is usually less than the static friction.

Rolling Friction

When one body rolls over the other, friction is created between the two surfaces. However, the frictional force of rolling is generally less than that of sliding.

Kinetic Friction

Kinetic friction describes the friction that occurs when things are in motion.

### Friction- Both Friend and Enemy

Extramarks NCERT Solutions for Class 8 Science Chapter 12 explains that friction has benefits, so it is seen as a friend, but it also has drawbacks, so it is regarded as an enemy. Friction may be beneficial or detrimental, depending on the situation. As a result, it is an unavoidable evil.

NCERT Solutions for Class 8 Science Chapter 12 by Extramarks gives you some advantages of friction as follows:

• We can write on paper because of the friction between the pen and the paper.
• Standing, walking, and running are all made possible by friction between our feet and the earth.
• The friction between the road surface and our cars’ tyres allows our vehicles to go along the road without sliding.

NCERT Solutions for Class 8 Science Chapter 12 by Extramarks gives you some disadvantages of friction as follows:

• As their motion is resisted, moving things tend to stop or slow down due to friction.
• Friction generates heat, which leads to energy waste in machinery.
• Over time, friction is responsible for the wear and tear of moving components in machinery, shoe bottoms, and road tyres.

How does friction produce heat?

It is because friction involves breaking bonds, which causes particles to vibrate, increasing kinetic energy and heat.

### How do you increase and reduce friction?

Ways to Increase Friction:

• By firmly pushing the surfaces together, we may increase friction. For example, when we apply brakes to a bicycle or automobile, the brake pads are forced against a moving element of the wheel, resulting in increased friction force.
• The roughness of the surfaces that come into contact can also be enhanced to create friction. Threading shoes and tyres, for example, is done to improve friction, which allows them to travel over the road without slipping.

Ways to Decrease Friction:

• By polishing the surfaces in contact, the frictional force operating between the sliding surfaces of two objects can be minimised.
• Oil, grease, graphite, or any other lubricant can minimise sliding friction between moving components of vehicles and machines. This is because the frictional force of rolling is generally less than that of sliding. As a result, sliding friction is often replaced with rolling friction by employing rollers, such as ball bearings between the hub and axles in machine and vehicle moving components.
• As a result, wheels are utilised in luggage and school backpacks for children to decrease friction.

Extramarks NCERT Solutions for Class 8 Science Chapter 12 explains how to Increase and Decrease friction in the above points. Extramarks are like a bundle of quality study material. Refer to the Extramarks website to gain more information.

### What is Drag Force?

Drag is a force particular only to liquids and is the term used for their frictional force.

The drag force on an item is determined by its speed and the form of its body, and the fluid’s composition.

Due to their streamlined structure, aircraft, boats, fish, and birds can travel through fluids, reducing friction and avoiding energy waste.

## NCERT Solutions for Class 8 Science Chapter 12 Exercise and Solutions

The best approach to absorb all of the topics of each chapter is to study the NCERT Solutions for that chapter. As a result, Extramarks provides NCERT Solutions for each chapter. Subject specialists prepare these Solutions to fulfil all of the students’ needs. Click on the below links to view NCERT Solutions for Class 8 Science Chapter 12:

• Class 8 Science Chapter 12: Very Short Answer Type Questions
• Class 8 Science Chapter 12: Short Answer Type Questions
• Class 8 Science Chapter 12: Long Answer Type Questions

Students may access NCERT Solutions for Class 8 Science Chapter 12 and other chapters by clicking here. In addition, students can also explore NCERT Solutions for other classes below.

By getting access to NCERT Solutions for Class 8 Science Chapter 12- Friction, students can easily understand all the chapter’s concepts.

NCERT Solutions Class 8 Science Chapter-wise List

### Key Features of NCERT Solutions for Class 8 Science Chapter 12

Extramarks NCERT solutions provide detailed and authentic answers to all the textbook questions. Through those, the students can understand, remember and retain answers to NCERT questions and thus, perform well in exams.

Our NCERT Solutions are customised for each chapter, considering all of the students’ demands. These answers are highly beneficial to students and help them understand things more easily and rapidly. A few reasons why you should choose Extramarks:

• These solutions have been made in simple language to make it convenient for the students to grasp the concepts.
• Based on the NCERT standards, Extramarks has compiled the most relevant material on this topic.
• These solutions help students save time while preparing.

Q.1 Fill in the blanks.

(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces.
(c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.

Ans-

(a) Friction opposes the motion between the surfaces in contact with each other.
(b) Friction depends on the nature of surfaces.
(c) Friction produces heat.
(d) Sprinkling of powder on the carrom board reduces friction.
(e) Sliding friction is less than the static friction.

Q.2 Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

(a) rolling, static, sliding
(b) rolling, sliding, static
(c) static, sliding, rolling
(d) sliding, static, rolling

Ans-

The correct option is (c).

Explanation: The force of friction acts due to irregularities between two surfaces. Static friction acts when an object is moved from rest. Sliding friction comes into play when an object slides over the surface of another object. In sliding friction, the time given for interlocking is very less. Hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Due to this, sliding friction is less than static friction. Also, the area of contact in case of rolling friction is smallest as compared to static or sliding friction. This area of contact changes gradually because of rolling. Thus, rolling friction is lesser than both static and sliding friction. So, the correct sequence is – static, sliding, rolling.

Q.3 Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(a) wet marble floor, dry marble floor, newspaper and towel.
(b) newspaper, towel, dry marble floor, wet marble floor.
(c) towel, newspaper, dry marble floor, wet marble floor.
(d) wet marble floor, dry marble floor, towel, newspaper

Ans-

The correct option is (a).

Explanation: Frictional force depends on the nature of surfaces in contact. The rougher the surface, the more is the friction between the surfaces in contact. According to roughness present in the given surfaces, we can arrange the force of friction acting between different surfaces as, wet marble floor, dry marble floor, newspaper and towel.

Q.4 Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

When the book slides on the desk, the force of friction acts between the book and the surface of the desk. The direction of frictional force is opposite to the direction of the motion of book and acts in upward direction.

Q.5 You spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?

Ans-

A person can walk because of the friction present between our feet and the ground. In order to walk, the person pushes the ground in the backward direction with his feet and the force of friction pushes it in the forward direction. When there is soapy water spilled on the floor, the force of friction between the ground and feet decreases. Thus, it becomes difficult to walk on the soapy floor.

Q.6 Explain why sportsmen use shoes with spikes.

Ans-

A sportsman wears shoes with spikes because these shoes give him a better grip while running. Due to this, force of friction between the shoes and the ground increases.

Q.7 Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Ans-

When a heavy object is kept on the floor, the interlocking of irregularities on the surfaces of box and floor become very powerful. It is because the two surfaces in contact are pressed harder. Thus, more force is required to overcome the interlocking. Therefore, to push the heavier box, Seema has to apply a larger force than Iqbal.

Q.8 Explain why sliding friction is less than static friction.

Ans-

Friction arises between two objects when irregularities present in the surfaces get interlocked with each other. In the case of sliding, the time given for interlocking is very small. Therefore, interlocking is not strong. Hence, less force is required to overcome from this interlocking. Thus, sliding friction is less than static friction.

Q.9 Give examples to show that friction is both a friend and a foe.

Ans-

Friction as a Friend:

1. Due to friction, a person is able to walk.
2. Friction between the tip of a pen and a paper helps us to write.

Friction as a Foe:

1. Due to friction, tyres and soles of shoes wear out.
2. Friction between different parts of machines can generate heat. This can damage the parts of machines.

Q.10 Explain why objects moving in fluids must have special shapes.

Ans-

An object moving through a fluid experiences an opposing force which tries to oppose its motion. This opposing force is also called the drag force. This force depends on the shape of the body. By giving the body a special shape, this force can be minimised. Thus, it becomes easier for the body to move through the fluid.

## FAQs (Frequently Asked Questions)

### 1. What is meant by friction as per Class 8th Science's chapter 12?

Friction is the force that prevents one item from moving when it comes into contact with another. It happens when two surfaces come into touch with each other. For example, the mechanical advantage of a machine is dropped due to friction. When we push a heavy box stored on the floor, for example, friction occurs between the surface of the floor and the bottom of the box.

### 2. What exactly are Lubricants when it comes to friction?

Lubricants are chemicals that are used to minimise friction. To improve efficiency, friction should be decreased. For example, oil, grease, or graphite can minimise friction between machine moving components. Then a thin coating forms, preventing the moving surfaces from rubbing against one other. As a result, the interlocking of imperfections is avoided to the most significant degree possible, and movement is smooth. Oil-based, water-based, and silicone-based lubricants are the three primary varieties.