FRICTION

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• Q1: Define Friction.
  Ans: Friction is the force that opposes the relative motion or tendency of motion between two surfaces in contact.
• Q2: State the advantages of Friction.
  Ans: The advantages of friction are:

  • ➔ It helps in walking without slipping
  • ➔ It allows vehicles to move and stop
  • ➔ It helps in writing on paper
  • ➔ It helps in holding objects
• Q3: State the types of friction.
  Ans: The types of friction are:

  • ➔ Static friction
  • ➔ Dynamic (kinetic) friction
  • ➔ Rolling friction
  • ➔ Fluid friction
• Q4: Define Static Friction.
  Ans: Static friction is the friction that acts when a body is at rest and prevents it from starting motion.
• Q5: Define Dynamic Friction.
  Ans: Dynamic friction is the friction that acts when a body is in motion.
• Q6: Define Limiting Friction.
  Ans: Limiting friction is the maximum value of static friction just before the body starts moving.
• Q7: Define Normal Friction.
  Ans: Normal friction is the frictional force acting perpendicular to the normal reaction between surfaces.
• Q8: Define Fluid Friction.
  Ans: Fluid friction is the resistance offered by fluids (liquids or gases) to the motion of a body moving through them.
• Q9: What is Angle of Repose?
  Ans: Angle of repose is the maximum angle of an inclined plane at which a body just begins to slide.
• Q10: What is Angle of Friction?
  Ans: Angle of friction is the angle between the resultant of normal reaction and friction force with the normal reaction.
• Q11: State the Laws of Friction.
  Ans: The laws of friction are:

  • ➔ Friction acts opposite to motion
  • ➔ It depends on nature of surfaces
  • ➔ It is independent of area of contact
  • ➔ It is proportional to normal reaction
• Q12: Define Coefficient of Friction.
  Ans: Coefficient of friction is the ratio of limiting friction to normal reaction.
  
  Formula:
  
  μ = F / R
• Q13: Define Sliding Friction.
  Ans: Sliding friction is the resistance experienced when one body slides over another body.
• Q14: Define Rolling Friction.
  Ans: Rolling friction is the resistance experienced when a body rolls over a surface.
• Q15: What are Ball Bearings?
  Ans: Ball bearings are mechanical devices that reduce friction between moving parts using small balls between surfaces.
• Q16: State the uses of Ball Bearings.
  Ans: The uses of ball bearings are:

  • ➔ Wheels of vehicles
  • ➔ Electric motors
  • ➔ Machinery shafts
• Q17: Briefly explain Stoke’s Law.
  Ans: Stoke’s law states that the drag force acting on a small spherical body moving in a fluid is directly proportional to its velocity, radius, and viscosity of the fluid.
  
  Formula:
  
  F = 6π η r v
• Q18: A body is at the point of sliding down on an inclined plane. The inclined plane makes an angle of 30 degrees with the horizontal. Find coefficient of friction.
  Ans: Given:
  Angle of inclination, θ = 30°
  
  At limiting condition:
  μ = tanθ
  
  μ = tan30°
  μ = 0.577
  
  Final Answer:
  Coefficient of friction = 0.577
• Q19: A block of wood of 700N is pulled along a horizontal surface. If the coefficient of friction between surface and wood is 0.4, find the force required.
  Ans: Given:
  Weight (Normal reaction), R = 700 N
  Coefficient of friction, μ = 0.4
  
  Step 1: Formula
  F = μR
  
  Step 2: Substituting values
  F = 0.4 × 700
  
  Step 3: Calculation
  F = 280 N
  
  Final Answer:
  Force required = 280 N