CBSE Class 8 Science Friction Worksheets with Answers - Chapter 12 - PDF
FAQs on CBSE Class 8 Science Friction Worksheets
1. What are the key factors that affect friction, and how might a question on this topic be structured for 3 marks in the Class 8 Science exam?
The two primary factors that affect friction are the nature of the surfaces in contact and the force pressing the surfaces together (normal force). For a 3-mark question, you would likely be asked to:
- State the two factors: Mention that rougher surfaces produce more friction than smoother ones, and a heavier object (or one pressed down harder) experiences more friction.
- Provide an example for each: For surface nature, compare pushing a box on a polished floor versus a carpet. For force, compare pushing a light box versus a heavy box on the same surface.
2. Explain with examples why friction is often called a 'necessary evil'. What kind of examples are important for the CBSE Class 8 exam?
Friction is called a 'necessary evil' because while it is essential for many of our daily activities, it also causes negative effects like wear and tear and energy loss. For your exam, you should prepare examples for both aspects:
- Necessary (Advantages): Friction enables us to walk without slipping, allows car brakes to work, and helps us write with a pen or pencil on paper.
- Evil (Disadvantages): It causes the soles of shoes and tyres to wear out, generates unwanted heat in machine parts, and reduces the efficiency of machines by opposing motion.
3. Differentiate between static, sliding, and rolling friction. Which one is the smallest, and why is this concept important?
This is a frequently asked concept in Class 8. The key differences are:
- Static Friction: The force of friction that comes into play when an object is at rest. It is a self-adjusting force that prevents an object from moving.
- Sliding Friction: The force that opposes motion when one object is sliding over another. It is slightly smaller than the maximum static friction.
- Rolling Friction: The force that opposes motion when an object rolls over a surface.
4. What is fluid friction (drag)? Explain why the bodies of aeroplanes and boats are streamlined, a common question in exams.
Fluid friction, also known as drag, is the frictional force exerted by fluids (liquids and gases) on objects moving through them. The shape of an object significantly affects the amount of drag. Aeroplanes and boats are given a special, pointed shape called a streamlined shape. This design allows the fluid (air or water) to flow smoothly around the object, minimising the resistance or drag. This is crucial for achieving higher speeds and better fuel efficiency, making it an important real-world application of reducing friction.
5. What types of questions, including MCQs, can be expected from the topics of increasing and reducing friction?
From these topics, you can expect a variety of question formats in your exam:
- MCQs (Multiple Choice Questions): These might ask you to identify an example of increasing friction (e.g., treads in tyres) or reducing friction (e.g., using lubricants).
- Short Answer Questions (2-3 marks): These questions often ask for methods to increase or decrease friction. For example, 'Give two methods to reduce friction' (Answers: using ball bearings, lubrication, polishing surfaces) or 'Why do gymnasts apply a coarse substance to their hands?' (Answer: to increase friction for a better grip).
6. From an exam perspective, how would you explain why it is easier to roll a log than to slide it?
To answer this important application-based question, you must use the correct terminology from the chapter. The reason it's easier to roll a log than to slide it is because rolling friction is significantly less than sliding friction. When you slide the log, a large surface area is in contact with the ground, creating high sliding friction. However, when you roll the log, the area of contact at any given moment is much smaller, resulting in very low rolling friction. This massive reduction in opposing force requires less effort to move the log.
7. If friction were to suddenly disappear, what would be the immediate consequences? Explain with three important examples.
This is a Higher Order Thinking Skills (HOTS) question that tests deep understanding. If friction disappeared, our world would be chaotic. Key consequences include:
- Inability to Move or Stop: We wouldn't be able to walk, as our feet would just slip. Similarly, vehicles could not start moving, and once moving, their brakes would not work to stop them.
- Objects Wouldn't Stay Put: Any object placed on a surface, especially a slightly inclined one, would slide off. We couldn't hold a glass of water, and nails or screws would not hold things together.
- No Fire or Writing: We couldn't light a matchstick, as it requires friction to ignite. It would also be impossible to write with a pencil or pen, as there would be no friction between the tip and the paper.
