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Q1. Friction is caused mainly due to:
Friction is caused mainly due to the irregularities (roughness) on the surfaces in contact. Even apparently smooth surfaces have microscopic bumps and valleys that interlock, creating resistance to motion. Smoothness reduces friction, but irregularities are the main cause of friction. Colour and temperature do not cause friction directly.
Q2. The force that opposes the relative motion between two surfaces in contact is called:
Frictional force is the force that opposes the relative motion between two surfaces in contact. It acts parallel to the surfaces and opposite to the direction of motion or attempted motion. Gravitational force pulls objects towards the Earth, magnetic force acts between magnets, and electrostatic force acts between charged bodies.
Q3. The friction experienced by a body when it is sliding over another surface is called:
The friction experienced when a body is sliding over another surface is called sliding friction (or dynamic friction). Static friction acts when the body is at rest, rolling friction acts when a body rolls, and fluid friction acts in liquids and gases. Sliding friction is the force that opposes sliding motion.
Q4. The friction that acts when a body is just about to start moving is called:
Static friction is the friction that acts when a body is at rest and a force is applied to start its motion. It prevents the body from moving and increases up to a maximum limit. Sliding friction acts during motion, rolling friction acts when an object rolls, and fluid friction acts in fluids.
Q5. The maximum value of static friction that must be overcome to start moving an object is called:
The maximum value of static friction that must be overcome to start moving an object is called limiting friction. It is the upper limit of static friction. Once the applied force exceeds limiting friction, the object starts moving, and sliding friction comes into play. Sliding friction is less than limiting friction.
Q6. The first law of limiting friction states that limiting friction is:
The first law of limiting friction states that limiting friction is directly proportional to the normal reaction (the perpendicular force pressing the surfaces together). It is not independent of the nature of surfaces, inversely proportional, or always equal to weight. The normal reaction is the force pressing the surfaces together.
Q7. The second law of limiting friction states that limiting friction depends on:
The second law of limiting friction states that limiting friction depends on the nature and roughness of the surfaces in contact. Rough surfaces have more friction. It does not depend on colour, area of contact, or temperature directly. The nature of the surfaces is a key factor.
Q8. The third law of limiting friction states that for two given surfaces, limiting friction is:
The third law of limiting friction states that for two given surfaces, limiting friction is independent of the area of contact. This means that increasing or decreasing the contact area does not change the limiting friction, as long as the normal reaction is constant. It does not depend on area, shape, or velocity.
Q9. Rolling friction is caused because:
Rolling friction is caused because the rolling object and the surface deform slightly at the point of contact. This deformation creates a small resistance to motion. Rolling objects are not smooth or free of irregularities, and rolling friction is not the same as sliding friction.
Q10. Which of the following is an example of rolling friction?
Rolling friction occurs when an object rolls over a surface. A ball rolling on the ground is an example of rolling friction. Pushing a box and writing with chalk are examples of sliding friction, and rubbing hands is also sliding friction. Rolling friction is generally less than sliding friction.
Q11. Which of the following is NOT an example of rolling friction?
A book sliding off a table is an example of sliding friction, not rolling friction. A bicycle wheel, marbles rolling, and a suitcase with wheels all involve rolling friction. Rolling friction occurs when an object rolls, while sliding friction occurs when an object slides.
Q12. Rolling friction is generally ______ than sliding friction.
Rolling friction is generally much smaller than sliding friction. This is why it is easier to move objects on wheels than to drag them. Wheels convert sliding friction into rolling friction, which reduces the resistance. Rolling friction is significantly less than sliding friction.
Q13. The difference between static friction and dynamic (sliding) friction is that:
Static friction is usually greater than dynamic (sliding) friction. This is why it is harder to start moving an object than to keep it moving. Static friction must be overcome to set the object in motion, while sliding friction is lower once motion has started.
Q14. When a body is moving through a gas or a liquid, the friction experienced is called:
Fluid friction is the friction experienced by a body moving through a gas or a liquid. It is also called drag. Rolling friction is for rolling objects, sliding friction is for sliding objects, and static friction is for stationary objects. Fluid friction is experienced in fluids.
Q15. The friction due to water is also called:
The friction due to water is called water drag or hydrodynamic drag. Air resistance is the friction due to air. Rolling friction is for rolling objects, and static friction is for stationary objects. Fluid friction in water is specifically called water drag.
Q16. The friction due to air is also called:
The friction due to air is called air resistance or aerodynamic drag. Water resistance is for water, rolling friction is for rolling objects, and limiting friction is the maximum static friction. Air resistance acts on objects moving through the air.
Q17. Which of the following shapes experiences the least air resistance?
A streamlined shape (like a teardrop) experiences the least air resistance because it allows air to flow smoothly around it. Flat sheets, square boxes, and cubes have more drag because they create turbulence. Streamlined shapes are used in cars, airplanes, and ships to reduce drag.
Q18. A ball rolling on the ground eventually stops because of:
A ball rolling on the ground eventually stops because of frictional force. Friction opposes the motion and gradually slows the ball down until it stops. Gravity pulls the ball downward, but friction is the force that stops horizontal motion. Magnetic and electrostatic forces are not involved.
Q19. Which of the following is a benefit of friction?
Friction is beneficial in many ways: it allows us to write (friction between pen and paper), cars to move without skidding (friction between tyres and road), and us to walk without slipping (friction between shoes and ground). These are all important uses of friction. Without friction, these activities would be impossible.
Q20. The friction between the brake pads and the wheel of a bicycle is an example of:
The friction between brake pads and the wheel of a bicycle is beneficial because it helps the bicycle stop. This is a controlled use of friction for safety. Harmful friction causes wear and tear, rolling friction is when objects roll, and fluid friction is in fluids. This friction is useful.
Q21. The friction that allows a nail to stay fixed in a wall is:
Static friction allows a nail to stay fixed in a wall. The friction between the nail and the wall prevents the nail from sliding out. Rolling friction is for rolling objects, fluid friction is in fluids, and sliding friction is when objects slide. Static friction holds the nail in place.
Q22. Which of the following is an example of friction due to gases?
A parachute descending through air experiences air resistance, which is friction due to gases. A boat moving through water experiences fluid friction due to liquids. A wheel rolling on sand and a block sliding on ice involve solid friction. Air resistance is friction due to gases.
Q23. The friction between a car tyre and a wet road is:
The friction between a car tyre and a wet road is less than on a dry road because water acts as a lubricant. This reduces the grip and increases the risk of skidding. On a dry road, there is more friction because the surfaces are in direct contact.
Q24. A matchstick lights up when struck against a rough surface because of:
A matchstick lights up because friction between the match head and the rough surface produces heat. This heat raises the temperature to the ignition point of the chemicals on the match head. Static electricity, magnetic force, and fluid friction are not involved in this process.
Q25. The soles of shoes wear out after prolonged use because of:
The soles of shoes wear out due to sliding friction between the soles and the ground. As we walk, the sliding action causes abrasion and wear. Rolling friction is for rolling objects, fluid friction is in fluids, and static friction acts when objects are at rest. Sliding friction causes wear and tear.
Q26. Which of the following increases friction?
Making a surface rough increases friction because rough surfaces have more irregularities that interlock. Oil, ball bearings, and air cushions are all methods to reduce friction. Rough surfaces provide more grip and resistance, which is useful in many applications like soles of shoes and tyres.
Q27. Which of the following decreases friction?
Lubricants like oil or grease decrease friction by creating a thin layer between surfaces, reducing direct contact. Sand on icy roads increases friction, rough soles increase friction, and brake pads are used to increase friction to stop vehicles. Lubrication is a common method to reduce friction.
Q28. Ball bearings are used in machines to:
Ball bearings are used to convert sliding friction into rolling friction, which is much smaller. This reduces friction and wear in machines. Ball bearings do not increase friction, wear, or weight; they make motion smoother and more efficient.
Q29. A ship is given a streamlined shape to:
A ship is given a streamlined shape to decrease fluid friction (water drag). A streamlined shape allows water to flow smoothly around the ship, reducing resistance and making it more fuel-efficient. It is not for looks or weight; the primary purpose is to reduce friction.
Q30. Static friction is a self-adjusting force. This means:
Static friction is self-adjusting, meaning it increases or decreases to match the applied force, up to a maximum limit (limiting friction). It does not have a fixed value and is not always zero. It adjusts itself to prevent motion until the limiting value is reached.
Q31. A person finds it easier to push a heavy suitcase on wheels than to drag it without wheels because:
It is easier to push a suitcase on wheels because rolling friction is less than sliding friction. Wheels convert sliding friction into rolling friction, which requires less force to overcome. The weight of the suitcase does not change; it is the type of friction that is reduced.
Q32. When a body is moving through a fluid, the fluid friction depends on:
Fluid friction depends on the shape of the body (streamlined shapes reduce drag), the speed of the body (higher speed increases drag), and the nature of the fluid (viscosity). All these factors influence the amount of fluid friction experienced by a moving body.
Q33. The friction between two surfaces can be reduced by:
Friction can be reduced by using a lubricant, which creates a thin layer between surfaces and reduces direct contact. Making surfaces rougher increases friction, increasing the force pressing them together also increases friction, and increasing the area of contact does not significantly affect friction for given surfaces.
Q34. The force of friction always acts:
Friction always acts opposite to the direction of motion or the attempted motion. It resists movement and tries to prevent relative motion between surfaces. It does not act in the direction of motion, perpendicular, or randomly.
Q35. Which of the following is NOT a benefit of friction?
Wearing out of machine parts is a disadvantage of friction, not a benefit. Writing, walking, and holding objects are benefits of friction. The wearing out of parts is harmful because it causes damage and reduces the life of machinery.
Q36. The limiting friction between two surfaces does NOT depend on:
Limiting friction does not depend on the area of contact between the surfaces. It depends on the normal reaction, the nature of the surfaces, and their roughness. The area of contact does not affect the limiting friction for given surfaces.
Q37. A ball rolling on a rough ground stops faster than on a smooth ground because:
A ball on a rough ground stops faster because rough ground provides more rolling friction. The irregularities on the rough surface increase resistance. Smooth ground has less friction, so the ball rolls farther. Rough ground does not have less friction or no friction.
Q38. Which of the following statements about static friction is correct?
Static friction is generally greater than sliding friction. It takes more force to start moving an object (to overcome static friction) than to keep it moving (sliding friction). Static friction is not less, equal, or zero when no force is applied; it adjusts to the applied force up to a limit.
Q39. The force required to keep an object moving at a constant speed on a horizontal surface is equal to:
To keep an object moving at constant speed on a horizontal surface, the applied force must equal the sliding friction. If the applied force is greater, the object accelerates; if less, it slows down. The sliding friction is the force opposing the motion. Static friction is not involved in constant motion.
Q40. A cyclist stops pedalling but the bicycle still moves some distance before stopping. This happens because:
When the cyclist stops pedalling, the bicycle continues to move due to inertia, but rolling friction and air resistance gradually slow it down and eventually stop it. Friction is acting; it is what slows the bicycle. The bicycle is not on ice; it is the friction that causes it to stop.
Q41. The friction due to liquids is generally ______ than friction due to gases.
Friction due to liquids (water, oil) is generally greater than friction due to gases (air). Liquids are denser and more viscous than gases, so they offer more resistance to motion. For example, moving through water is harder than moving through air. Greater friction means more drag.
Q42. Which of the following is an example of harmful friction?
Friction between moving parts of a machine that generates heat and causes wear is harmful. It damages components and wastes energy. The other options are benefits of friction. Road and tyre friction helps vehicles move, ground and shoe friction helps us walk, and chalk and blackboard friction helps writing.
Q43. A pencil leaves a mark on paper because of:
A pencil leaves a mark on paper due to sliding friction between the pencil lead and the paper. The friction causes the lead to wear off and deposit on the paper. Rolling friction is for rolling objects, fluid friction is in fluids, and static friction acts when objects are at rest.
Q44. The friction between a moving car and the air is an example of:
The friction between a moving car and the air is fluid friction, specifically air resistance. It is a type of drag that opposes the motion of the car. Rolling friction is between the tyres and the road, sliding friction is between sliding surfaces, and static friction acts when objects are at rest.
Q45. If you try to push a heavy cupboard and it does not move, the force of friction acting is:
When you push a heavy cupboard and it does not move, the force of friction acting is static friction. Static friction opposes the applied force and prevents motion. Sliding friction acts when the object is moving, rolling friction is for rolling objects, and fluid friction is in fluids.
Q46. The soles of shoes are made with treads (grooves) to:
Treads on shoe soles are designed to increase friction between the sole and the ground, preventing slipping. They provide better grip, especially on wet or slippery surfaces. The treads do not reduce friction; they increase it for safety.
Q47. A train moves on rails. The friction between the train wheels and the rails is:
The friction between train wheels and the rails is rolling friction because the wheels roll over the rails. This reduces friction compared to sliding friction, making it more efficient. Sliding friction would occur if the wheels were skidding, and static friction acts at rest.
Q48. Which of the following increases friction?
Adding sand on an icy road increases friction by providing more roughness, which helps vehicles get grip. Polishing a surface decreases friction, adding water can act as a lubricant and decrease friction, and ball bearings decrease friction by converting sliding to rolling. Sand increases friction.
Q49. The heat produced when you rub your hands together is due to:
The heat produced when you rub your hands together is due to sliding friction. The friction between the surfaces generates heat energy. Static electricity is not the cause, fluid friction is in fluids, and rolling friction is for rolling objects. Sliding friction is the correct answer.
Q50. A book lying on a table does not move by itself because:
A book on a table does not move because static friction balances any small forces that might act on it, preventing motion. There are forces acting (gravity, normal reaction), but static friction adjusts to keep the book at rest. The table is not frictionless, and gravity is acting. Static friction is the reason it stays still.