Long Answer Questions on Friction for Class 8
- Why is friction considered a necessary evil?
Answer:
Friction is essential for many everyday activities (such as walking, driving, and holding objects). Thus it is necessary. But it also causes problems such as wear and tear of machine parts and reduces efficiency by wasting energy into heat. Thus, it acts as evil. Hence, the friction is considered a necessary evil. - What is rolling friction? Arrange the following in descending order of magnitude: (i) static friction (ii) sliding friction (iii) rolling friction.
Answer:
Rolling friction is the frition force that acts when an object rolls over a surface. It is generally much less than sliding friction. The order of magnitude from greatest to least is: Static friction > Sliding friction > Rolling friction - Describe the factors on which the force of friction depends.
Answer:
The force of friction depends on several factors:
1. Nature of the surfaces: Rougher surfaces cause higher friction because there could be better interlocking.
2. Normal force between two surfaces: The frictional force is proportional to the normal force pressing the two surfaces together. More weight or pressure increases friction.
3. Surface area: Contact surface area does not affect friction. - How can friction between two surfaces be reduced?
Answer:
Friction between two surfaces can be reduced by:
Lubrication: Applying a lubricant (like oil or grease) between the surfaces.
Polishing: Smoothing the surfaces reduce the roughness and hence the friction.
Using rollers or ball bearings: These change sliding friction into rolling friction, which is much lower. - What is meant by saying that friction is a self-adjusting force?
Answer:
Saying that friction is a self-adjusting force means that it adjusts itself to match the applied force up to a certain limit (the maximum static friction). When a force is applied to an object at rest, the frictional force increases to oppose the applied force until the object begins to move. This self-adjusting nature of friction ensures that objects remain stationary until the applied force exceeds the maximum static friction.
