MOMENTS AND COUPLES

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• Q1: Define Moment. Write its unit and formula.
  Ans: Moment is the turning effect of a force about a point or axis.
  Unit: Newton-meter (N·m)
  Formula:
  
  Moment = Force × Distance
  M = F × d
• Q2: State the types of Moment.
  Ans: The types of moments are:

  • ➔ Clockwise Moment
  • ➔ Anticlockwise Moment
• Q3: Define Line of Action.
  Ans: Line of action is the imaginary straight line along which a force acts.
• Q4: Define Torque. Write its formula.
  Ans: Torque is the turning effect of a force about an axis.
  Formula:
  
  τ = F × r
• Q5: What is Clockwise Torque?
  Ans: Clockwise torque is the turning effect of a force that rotates a body in the clockwise direction.
• Q6: What is Anticlockwise Torque?
  Ans: Anticlockwise torque is the turning effect of a force that rotates a body in the opposite (anticlockwise) direction.
• Q7: Define Couple of Forces.
  Ans: A couple of forces consists of two equal and opposite forces acting parallel to each other but in opposite directions, producing rotation only.
• Q8: State the principle of Moments.
  Ans: The principle of moments states that for a body in equilibrium:
  Sum of clockwise moments = Sum of anticlockwise moments
• Q9: What is a Lever? What is it used for?
  Ans: A lever is a rigid bar that rotates about a fixed point called fulcrum.
  It is used to lift heavy loads with less effort.
• Q10: State the principle of Lever.
  Ans: The principle of lever states:
  Effort × Effort arm = Load × Load arm
• Q11: Name the types of Lever.
  Ans: Types of levers are:

  • ➔ Class I Lever
  • ➔ Class II Lever
  • ➔ Class III Lever
• Q12: What is Class I Lever?
  Ans: In Class I lever, the fulcrum lies between effort and load.
  Example: Seesaw
• Q13: What is Class II Lever?
  Ans: In Class II lever, the load lies between fulcrum and effort.
  Example: Wheelbarrow
• Q14: What is Class III Lever?
  Ans: In Class III lever, the effort lies between fulcrum and load.
  Example: Human arm
• Q15: State the mechanical advantage of Lever.
  Ans: Mechanical Advantage (M.A) of a lever is:
  M.A = Load / Effort
  Also,
  M.A = Effort arm / Load arm
• Q16: What is Cranked Lever?
  Ans: A cranked lever is a bent lever used to change the direction of force and provide better mechanical advantage.
• Q17: State the uses of Cranked Lever.
  Ans: Uses of cranked lever are:

  • ➔ In machines to change direction of motion
  • ➔ In engines
  • ➔ In mechanical presses
• Q18: What is Steel Yard?
  Ans: A steel yard is a weighing device that uses the principle of moments to measure weight using a movable counterweight.
• Q19: What is a Lever Safety Valve?
  Ans: A lever safety valve is a device used in boilers to release excess pressure using a lever and weight system.
• Q20: Describe the working principle of Safety Valve.
  Ans: A safety valve works on the principle of moments.
  When pressure inside the boiler increases beyond limit, it lifts the valve against the weight and releases steam, preventing explosion.
• Q21: The mechanical advantage of a lever is 5. If its effort arm is 3m, find Load arm.
  Ans: Given:
  M.A = 5
  Effort arm = 3 m
  
  Formula:
  M.A = Effort arm / Load arm
  
  5 = 3 / Load arm
  
  Load arm = 3 / 5 = 0.6 m
  
  Final Answer:
  Load arm = 0.6 m