Physics Chapter 6: Forces and Moments
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Questions and Answers

What defines collinear forces?

  • Forces that meet at one point
  • Forces whose lines of action lie on the same line (correct)
  • Forces that do not meet at one point
  • Forces acting on different planes

    • Which type of forces are described as non-coplanar concurrent forces?

  • Forces that meet at one point but do not lie on the same plane (correct)
  • Forces that do not meet but lie in the same plane
  • Forces that meet at multiple points
  • Forces that act on different lines

    • Which characteristic of a force indicates its intensity?

  • Point of application of the force
  • Direction of the force
  • Nature of the force
  • Magnitude of the force (correct)

    • What effect can a force have on a body at rest?

    <p>It can set the body in motion</p> Signup and view all the answers

    Which of the following is a characteristic maintained while determining the effects of a force?

    <p>Direction of the line of action</p> Signup and view all the answers

    If a body is already in motion, what can a force do to it?

    <p>Accelerate or change its motion</p> Signup and view all the answers

    What is the formula for the moment of a force about point O?

    <p>P × OC</p> Signup and view all the answers

    Which of these describes coplanar non-concurrent forces?

    <p>Forces that do not meet at one point but lie in the same plane</p> Signup and view all the answers

    What are the units of moment when force is measured in Newtons and distance in meters?

    <p>Newton-meter</p> Signup and view all the answers

    What effect does a force produce when it retards the motion of a body?

    <p>Sets the body in a non-moving state</p> Signup and view all the answers

    Which type of moment is considered positive according to general conventions?

    <p>Clockwise moment</p> Signup and view all the answers

    According to Varignon’s Principle, what is true about the algebraic sum of the moments?

    <p>It equals the moment of the resultant force about the same point.</p> Signup and view all the answers

    What is the least pull required to turn a wheel over the corner of a block if the wheel has a diameter of 600 mm?

    <p>2.5 kN</p> Signup and view all the answers

    If a force causes an anticlockwise moment, what is its conventionally assigned value?

    <p>Negative</p> Signup and view all the answers

    Which scenario best illustrates the concept of a clockwise moment?

    <p>A door swinging outward</p> Signup and view all the answers

    What does the area of triangle ABO represent in the context of moments?

    <p>Half the moment of the force about point O</p> Signup and view all the answers

    What is the formula for calculating the moment of inertia of a force about a point?

    <p>Force multiplied by the distance</p> Signup and view all the answers

    What are the units for moment of inertia if area is in mm² and length is in mm?

    <p>mm⁴</p> Signup and view all the answers

    For which type of section is the theorem of perpendicular axis applicable?

    <p>I-section</p> Signup and view all the answers

    Which of the following dimensions defines the height and radius of a circular solid cone?

    <p>40 mm height and 30 mm radius</p> Signup and view all the answers

    What is the second moment of force commonly called?

    <p>Moment of inertia</p> Signup and view all the answers

    Which shape can have a hollow rectangular section's moment of inertia calculated?

    <p>Rectangle</p> Signup and view all the answers

    What is the purpose of the theorem of parallel axes when calculating moment of inertia?

    <p>To find the moment of inertia about any axis parallel to the centroidal axis</p> Signup and view all the answers

    What dimensions are given for the unequal angle section example?

    <p>100 mm × 80 mm × 20 mm</p> Signup and view all the answers

    What is the maximum value of frictional force called when a body just begins to slide over another surface?

    <p>Limiting friction</p> Signup and view all the answers

    Which of the following statements about the coefficient of friction is true?

    <p>It is the ratio of limiting friction to the normal reaction.</p> Signup and view all the answers

    What does the angle of friction relate to in terms of a body on an inclined plane?

    <p>The angle at which the body begins to slide down.</p> Signup and view all the answers

    Which law of static friction states that the force of friction acts in the opposite direction of motion?

    <p>First law of static friction</p> Signup and view all the answers

    How does the force of friction depend on the surfaces in contact?

    <p>It is independent of the area of contact.</p> Signup and view all the answers

    What is the angle of repose?

    <p>The steepest angle at which a body can rest without sliding.</p> Signup and view all the answers

    Which of the following describes dynamic friction?

    <p>It opposes the motion of a body already in motion.</p> Signup and view all the answers

    What is defined as a couple in mechanics?

    <p>Two equal and opposite parallel forces</p> Signup and view all the answers

    What does the arm of a couple refer to?

    <p>The perpendicular distance between the lines of action of the two forces</p> Signup and view all the answers

    Which law of friction states that the limiting friction has a constant ratio to the normal reaction?

    <p>Second law of static friction</p> Signup and view all the answers

    What is the moment of a couple calculated from?

    <p>The product of one force and the arm of the couple</p> Signup and view all the answers

    Which of the following best describes a clockwise couple?

    <p>It rotates the body in a clockwise direction</p> Signup and view all the answers

    Which characteristic is TRUE for a couple?

    <p>The algebraic sum of the forces is zero</p> Signup and view all the answers

    How can multiple co-planar couples be summarized?

    <p>They can be adjusted to a single couple based on their moments</p> Signup and view all the answers

    In the context of a couple, what does the term 'negative couple' refer to?

    <p>An anticlockwise couple</p> Signup and view all the answers

    What happens when a couple is applied to a body?

    <p>It causes rotation without translational motion</p> Signup and view all the answers

    What is the definitive characteristic of a center of gravity (C.G.)?

    <p>It acts through the whole weight of the body.</p> Signup and view all the answers

    Where is the center of gravity located for a uniform rod?

    <p>At the midpoint of the rod.</p> Signup and view all the answers

    For a rectangle, where is the center of gravity found?

    <p>At the intersection of its diagonals.</p> Signup and view all the answers

    What is the center of gravity for a triangle determined by?

    <p>The intersection of its medians.</p> Signup and view all the answers

    How far is the center of gravity from the base of a semicircle?

    <p>$ rac{4r}{3 imes ext{π}}$</p> Signup and view all the answers

    Where is the center of gravity for a hemisphere measured from its base?

    <p>$ rac{3r}{8}$</p> Signup and view all the answers

    For a right circular solid cone, where is the center of gravity located relative to its base?

    <p>$ rac{h}{4}$</p> Signup and view all the answers

    What can be inferred about the center of gravity of a cube?

    <p>It's at a distance of $ rac{l}{2}$ from every face.</p> Signup and view all the answers

    Study Notes

    Engineering Mechanics Lecture Notes

    • Engineering Mechanics is the branch of applied science that deals with the laws and principles of mechanics, along with their applications to engineering problems.
    • The subject can be divided into two main groups: Statics and Dynamics.
    • Statics deals with forces and their effects on bodies at rest.
    • Dynamics deals with forces and their effects on bodies in motion, further sub-divided into Kinetics and Kinematics.
    • Kinetics analyses motion caused by forces.
    • Kinematics analyzes motion without considering the forces causing it.
    • A rigid body is a solid body in which deformation is negligible.
    • Force is an agent that tends to cause, destroy, or change motion.
    • Systems of Forces:
      • Coplanar forces: Forces whose lines of action lie in the same plane.
      • Collinear forces: Forces whose lines of action lie on the same line.
      • Concurrent forces: Forces which meet at a common point.
      • Coplanar concurrent forces: Coplanar forces that meet at a common point.
      • Coplanar non-concurrent forces: Coplanar forces that do not meet at a common point.
      • Non-coplanar concurrent forces: Forces that meet at a common point, but their lines of action do not lie in the same plane.
      • Non-coplanar non-concurrent forces: Forces that do not meet at a common point and their lines of action do not lie in the same plane.
      • Methods for finding the resultant force: Analytical methods (parallelogram law, method of resolution) and graphical methods.

    Chapter Contents

    • Fundamentals of Engineering Mechanics: Covers basic concepts. (pages 1-11)
    • Equilibrium: Discusses forces in equilibrium. (pages 12-17)
    • Friction: Explains frictional forces. (pages 18-32)
    • Centroid & Moment of Inertia: Details centroids and moment of inertia. (pages 33-46)
    • Simple Machines: Covers various simple machines. (pages 47-64)
    • Dynamics: Details dynamics concepts. (pages 65-72)

    Additional Topics

    • Characteristics of forces: Magnitude, direction, line of action, and the point of application.
    • Effects of forces: Change in motion, motion retardation, and internal stresses.
    • Principle of transmissibility: A force acting at a given point of a rigid body can be moved along its line of action.
    • Principle of superposition: The combined effect of a force system is the sum of the effects of individual forces.
    • Resolution of a force: Breaking down a force into components.

    Equilibrium

    • Different concepts of equilibrium
    • Two force, Three force and Four Force Principles
    • Lami's Theorem

    Friction

    • Introduction to friction
    • Static Friction
    • Dynamic Friction
    • Limiting Friction
    • Coefficient of Friction
    • Angle of Friction

    Moment of a Force

    • Moment of a force is equal to the product of force and perpendicular distance from the axis.
    • Units are Newton-meter. (N-m.)
    • Types of Moments
      • Clockwise moments
      • Anticlockwise moments
    • Principle / Law of moments
    • Varignon's Principle

    Moment of a Couple

    • A couple is a pair of equal and opposite parallel forces with different lines of action.
    • The moment of a couple is equal to the product of the force acting in the couple and the perpendicular distance between the lines of action of the two forces.

    Equilibrium of a Body on Inclined Planes

    • Forces on a rough inclined plane.
    • Conditions for Equilibrium.

    Equilibrium of a Body on a Horizontal Plane (with Force Acting Horizontally)

    Center of Gravity

    • Centroid of plane figures
    • Locating the center of mass by geometry.
    • Methods for Locating Centers of Gravity
      • Centre of Gravity of Simple Figures
      • Centre of Gravity by Geometry
    • Axis of Reference.
    • Locating the centre of gravity of unsymmetrical sections.
    • Symmetry rules in locating the center of gravity

    Moment of Inertia

    • Moment of Inertia formula.
    • The moment of inertia of a plane area is a measure of a body's resistance to angular acceleration.
    • Moment of Inertia of a Rectangular Section formula
    • Moment of Inertia of a Hollow Rectangular Section formula
    • Theorem of Perpendicular Axis
    • Moment of Inertia of Circular Section formulae
    • Theorem of Parallel Axis

    Simple Machines

    • Simple Machine definition
    • Compound Machine definition
    • Lifting Machine definition
    • Mechanical Advantage definition.
    • Input of a machine definition
    • Output of a machine Definition
    • Efficiency of a machine definition
    • Ideal Machine definition
    • Velocity Ratio definition
    • Simple Gear Train
    • Compound Gear Train

    Simple Lifting Machines

    • Wheel and axle
    • Single Purchase Crab Winch

    Screw Jack

    • Principle
    • Components
    • Equation of efficiency and mechanical advantage

    Hoisting Machines

    • Derricks (types and uses)

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    Lecture Notes on Engineering Mechanics PDF

    Description

    Test your knowledge on the concepts of collinear forces, moments, and their effects on bodies in motion or at rest. This quiz covers various aspects of force application, including characteristics, units, and principles like Varignon’s Principle. Perfect for students studying mechanics in physics.

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