Friction

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Q1. Which of the following is a disadvantage of friction?
Friction causes wear and tear in moving parts of machines, which is a disadvantage. Walking, braking, and writing are all advantages of friction. When machine parts rub against each other, the surfaces gradually wear down, leading to reduced efficiency and eventual failure of the machinery.

Q2. Friction is called a necessary evil because:
Friction is called a necessary evil because it has both useful and harmful effects. It is necessary for activities like walking, writing, and gripping, but it also causes wear and tear, generates heat, and wastes energy. We cannot eliminate it completely, but we can reduce its harmful effects.

Q3. Which of the following is NOT a way to reduce friction?
Making surfaces rougher increases friction, not reduces it. Using lubricants, ball bearings, and polishing surfaces are all methods to reduce friction. Rough surfaces have more irregularities and therefore more friction. Smoothing surfaces reduces the interlocking between them.

Q4. Lubricants reduce friction by:
Lubricants reduce friction by creating a thin layer between the moving surfaces, which prevents direct contact and allows the surfaces to slide smoothly over each other. This reduces the interlocking of surface irregularities. Lubricants do not make surfaces rougher, increase weight, or make surfaces hotter.

Q5. Which of the following is an example of a lubricant?
Oil is a common lubricant used to reduce friction between moving parts. Sand, sawdust, and salt are not lubricants; they would actually increase friction due to their abrasive nature. Lubricants like oil, grease, and graphite reduce friction by creating a thin layer between surfaces.

Q6. Soap solution can be used to reduce friction because:
Soap solution acts as a lubricant by creating a thin, slippery film between surfaces, reducing friction. This is why soapy water makes surfaces slippery. It does not make surfaces rough, increase weight, or dry quickly. Its lubricating property is what reduces friction.

Q7. Fine powder (like talcum powder or graphite powder) reduces friction by:
Fine powders like talcum powder or graphite powder act as dry lubricants by creating a thin layer of particles that roll between surfaces, reducing friction. Graphite is often used in locks for this reason. They do not make surfaces sticky, increase roughness, or absorb all moisture.

Q8. Polishing a surface reduces friction because:
Polishing reduces friction by removing microscopic irregularities and making the surface smooth. A smooth surface has fewer points of contact and less interlocking, resulting in lower friction. Polishing does not make the surface rougher, add dust, or increase the area of contact.

Q9. Streamlining reduces friction by:
Streamlining reduces fluid friction (air or water resistance) by giving the object a shape that allows the fluid to flow smoothly around it. This reduces turbulence and drag. It does not make the object heavier, larger, or add rough patches.

Q10. Converting sliding friction into rolling friction reduces friction because:
Converting sliding friction into rolling friction reduces friction because rolling friction is much smaller than sliding friction. This is why wheels and ball bearings are used: they reduce the resistance to motion significantly. Rolling friction is less than sliding friction because there is less surface contact.

Q11. Which of the following is an example of converting sliding friction into rolling friction?
Ball bearings convert sliding friction into rolling friction, reducing resistance in machines like fans. Oiling is lubrication, polishing smooths surfaces, and adding sand increases friction. Ball bearings allow the parts to roll rather than slide, which is much more efficient.

Q12. The energy wasted in overcoming friction in machines usually appears as:
The energy wasted in overcoming friction in machines usually appears as heat energy. This is why moving parts become hot. The mechanical energy is converted into thermal energy due to friction. It does not appear as light, sound, or electrical energy in this context.

Q13. Friction causes wear and tear. This means:
Friction causes wear and tear, meaning surfaces gradually lose material and get damaged over time. This is because the rubbing action wears away particles from the surfaces. This can lead to the need for replacement or repair. It does not make objects cleaner or heavier.

Q14. Which of the following is a way to reduce friction in a bicycle chain?
Oiling the chain regularly is a way to reduce friction in a bicycle chain. The oil acts as a lubricant, reducing wear and making the chain move smoothly. Adding sand or making the chain rougher would increase friction. Heating would not reduce friction effectively.

Q15. Friction is said to be a necessary evil because without it:
Without friction, we would not be able to walk (no grip), vehicles would not move (no traction), and we could not write (no friction between pen and paper). Friction is necessary for these activities, but it also causes wear and tear, making it both essential and harmful.

Q16. Which of the following reduces friction by using a dry lubricant?
Graphite powder is a dry lubricant used in locks to reduce friction. Oil and soap solution are wet lubricants, and water does not reduce friction effectively. Graphite powder acts as a dry lubricant by creating a slippery layer between surfaces without moisture.

Q17. The shape of an aeroplane is streamlined to:
Aeroplanes are streamlined to decrease air resistance (fluid friction). A streamlined shape allows air to flow smoothly around the plane, reducing drag and improving fuel efficiency. It is not for looks or weight; the primary purpose is to reduce friction.

Q18. Why do athletes wear special smooth suits while swimming or cycling?
Athletes wear smooth suits to decrease friction (drag) with water or air. This helps them move faster by reducing resistance. The suits are designed to be smooth and streamlined, not to increase friction, look fashionable, or keep warm.

Q19. Which of the following statements about friction is correct?
Friction cannot be completely eliminated because even the smoothest surfaces have some irregularities. However, it can be reduced by various methods like lubrication, polishing, and using ball bearings. Friction is not always useful or harmful; it is both.

Q20. A heavy box is easier to move if we put rollers under it because:
Rollers make it easier to move a heavy box by converting sliding friction into rolling friction, which is much smaller. This reduces the resistance significantly. Rollers do not increase weight, make the box rougher, or increase the area of contact in a way that helps.

Q21. Excessive friction in machines can cause:
Excessive friction in machines causes overheating and damage to parts. The heat generated can degrade lubricants, cause expansion, and lead to mechanical failure. It reduces efficiency, not increases it. Proper lubrication is needed to prevent this.

Q22. Which of the following is a disadvantage of friction in a car engine?
In a car engine, friction causes engine parts to wear out and fuel efficiency to decrease as energy is wasted overcoming friction. Braking, tyre grip, and moving forward are advantages of friction. The wear and fuel loss are disadvantages.

Q23. Using soap solution on a glass stopper stuck in a bottle helps to remove it because:
Soap solution acts as a lubricant, reducing friction between the glass stopper and the bottle neck, making it easier to remove. It does not increase friction, make the glass expand, or contract. The slippery film allows the stopper to slide out.

Q24. Polishing a metal surface reduces friction. However, over-polishing can be harmful because:
Over-polishing can make a surface too smooth, causing it to lose necessary grip. This can be dangerous in applications where traction is needed, like on floors or tools. The surface does not become rough, gain weight, or increase heat due to polishing.

Q25. The use of lubricants in machines is important because they:
Lubricants are important because they reduce friction, heat, and wear in machines. They create a protective layer between moving parts, preventing direct contact. This improves efficiency and prolongs the life of the machine. They do not increase friction or wear.

Q26. A ship is given a streamlined shape to reduce friction with:
A ship is streamlined to reduce friction with both water and air. The shape allows the ship to move through water with less drag, and also reduces air resistance. It is not just for water or air alone, but both. The dock is not relevant.

Q27. Which of the following reduces friction by using a liquid lubricant?
Oil is a liquid lubricant used to reduce friction in a bicycle chain. Talcum powder and graphite are dry lubricants, and sand on ice increases friction for grip. Liquid lubricants like oil create a slippery film between surfaces.

Q28. Friction can be reduced by using fine powder because:
Fine powder reduces friction because the powder particles act as tiny rollers between the surfaces, allowing them to move more easily. This is how graphite powder works in locks. The powder does not make the surface rough, absorb heat, or increase weight.

Q29. Which of the following is NOT a disadvantage of friction?
Writing on paper is an advantage of friction, not a disadvantage. Wear and tear, heat generation, and energy waste are all disadvantages of friction. Friction is essential for writing because it allows the pencil/pen to leave a mark on the paper.

Q30. The treads (grooves) on car tyres are made to increase friction, but sometimes tyres are also made of special rubber compounds that reduce rolling friction. This shows that:
Tyres have treads to increase friction for grip, but the rubber compound is designed to reduce rolling friction. This shows that different surfaces and situations need different amounts of friction. Friction can be controlled and optimized for specific needs.

Q31. Ball bearings are used in ceiling fans and bicycles to:
Ball bearings convert sliding friction into rolling friction, which is much smaller and reduces wear and energy loss. They are used in fans and bicycles to make rotation smoother and more efficient. They do not increase friction, weight, or noise.

Q32. A lot of fuel is wasted in vehicles to overcome friction. This is an example of:
Wasting fuel to overcome friction is a disadvantage of friction. The energy lost as heat due to friction reduces fuel efficiency. Friction is necessary for vehicle movement, but the fuel wasted is a drawback.

Q33. Which of the following is a way to reduce friction between two solid surfaces?
Applying a lubricant like grease reduces friction between two solid surfaces by creating a thin layer that prevents direct contact. Making surfaces rougher increases friction, increasing force increases friction, and increasing area of contact does not significantly reduce friction.

Q34. When we say friction is a necessary evil, we mean that:
Friction is a necessary evil because it is both useful and harmful. It is essential for many activities but also causes problems like wear and energy loss. We cannot remove it completely because it is necessary, but we can reduce its harmful effects.

Q35. Streamlining is used in the design of:
Streamlining is used in the design of aeroplanes, cars, fish, and many other objects to reduce fluid friction. It is not limited to one type of object. Anything that moves through air or water benefits from a streamlined shape.

Q36. Which of the following reduces friction by smoothing out irregularities?
Polishing reduces friction by smoothing out irregularities on the surface. Oil lubricates, ball bearings convert to rolling friction, and streamlining reduces fluid friction. Polishing physically removes rough spots, making the surface smoother.

Q37. A zipper that is stuck can be fixed by applying:
A stuck zipper can be fixed by applying soap solution or wax, which acts as a lubricant to reduce friction and allow the zipper to slide smoothly. Sand, glue, and paint would not help; they would make it worse.

Q38. Which of the following statements about reducing friction is correct?
Friction can be reduced by various methods, but it cannot be completely eliminated because even the smoothest surfaces have some irregularities. It can be made very small but never zero. The other statements are incorrect.

Q39. The use of ball bearings in a skateboard wheel reduces friction by:
Ball bearings convert sliding friction into rolling friction, which is much smaller and allows the skateboard wheels to turn smoothly. This reduces wear and makes the ride smoother. It does not increase sliding, add lubricant, or make the wheel rough.

Q40. Why is it easier to pull a suitcase on wheels than to drag it?
It is easier to pull a suitcase on wheels because the wheels convert sliding friction into rolling friction, which is much smaller. This reduces the force needed to move the suitcase. The weight does not change, and it does not make it rougher or increase air resistance.

Q41. Friction between moving parts of a machine can cause the machine to become hot. This is a disadvantage because:
Heat generated by friction can damage machine parts and waste energy. Overheating can lead to expansion, melting of lubricants, and mechanical failure. It does not improve performance or reduce wear. This is a major disadvantage of friction.

Q42. A powder called talcum is used on carom boards to:
Talcum powder is used on carom boards to reduce friction, allowing the coins to slide smoothly across the board. It acts as a dry lubricant. It does not increase friction, make the board sticky, or clean the board.

Q43. Which of the following is an example of reducing friction by streamlining?
Streamlining involves shaping an object to reduce fluid friction. A race car with a pointed front and smooth curves is streamlined to reduce air resistance. Oiling, ball bearings, and polishing are other methods of reducing friction, but they are not streamlining.

Q44. Why do we use grease instead of oil in some machines like car wheel hubs?
Grease is used in some machines because it stays in place longer and does not drip like oil. This makes it suitable for applications where oil would run off. Grease does not increase friction; it reduces it. It is not a solid; it is a semi-solid lubricant.

Q45. If there were no friction, which of the following would happen?
If there were no friction, a moving car would never stop because there would be no friction to slow it down. Walking, driving, and writing would be impossible without friction. Friction is necessary for stopping and controlling motion.

Q46. Polishing a surface reduces friction, but why do we not polish the soles of our shoes?
We do not polish shoe soles because they would become too slippery, reducing friction and causing falls. We need friction for grip. Polishing would make them smooth and dangerous. It would not increase friction or damage the material in this way.

Q47. Friction can be reduced by using a lubricant. Which of the following is NOT a lubricant?
Sand is not a lubricant; it is an abrasive that increases friction. Motor oil, cooking oil, and graphite powder are all lubricants that reduce friction. Sand would cause wear and increase resistance, not reduce it.

Q48. The principle of converting sliding friction into rolling friction is used in:
Ball bearings convert sliding friction into rolling friction, reducing resistance. This principle is used in skateboards, fans, and many machines. Writing involves sliding friction, rolling dough uses rolling without bearings, and rubbing hands generates heat from sliding friction.

Q49. A car engine uses engine oil to reduce friction. What would happen if the engine runs without oil?
Without oil, the engine parts would experience excessive friction, leading to overheating and rapid damage. Oil is essential for lubrication, cooling, and protection. Without it, the engine would fail quickly. It would not run smoothly, consume less fuel, or be quieter.

Q50. Which of the following methods reduces friction by changing the shape of the object?
Streamlining reduces friction by changing the shape of an object to allow smooth flow of air or water. Oiling, ball bearings, and polishing are other methods, but they do not change the shape of the object. Streamlining specifically involves altering the shape to reduce fluid friction.