Introduction to applied mechanics

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Introduction to applied mechanics

  1. 1. CHAPTER 1 INTRODUCTION MISSAM Mechanical Dept. LJ Polytechnic
  2. 2. INTODUCTION OBJECTIVES Define force Classify forces Define Kinematics Define Kinetics MISSAM Mechanical Dept. LJ Polytechnic
  3. 3. INTRODUCTION WHAT ARE FORCES Forces enable us to start moving, stop moving, and change directions We manipulate the forces acting on us to maintain our balance in stationary positions (e.g. cyclist, diver) Simply defined, a force is a push or a pull Forces are exerted by objects on other objects MISSAM Mechanical Dept. LJ Polytechnic
  4. 4. INTRODUCTION WHAT ARE FORCES Forces come in pairs; the force exerted by one object on another is matched by an equal but oppositely directed force exerted by the second object on the first—Action and reaction Forces accelerate objects—Start, stop, speed up, slow down, or change direction SI unit is N (Newton) 1N force is the force that would accelerate a 1kg mass 1m/s2 1N = .225lb 1lb = 4.448N MISSAM Mechanical Dept. LJ Polytechnic
  5. 5. INTRODUCTION WHAT ARE FORCES Describe the force a shot-putter exerts on a shot at the instant shown in Figure 1.1 Factors we want to know: Size Point of application Direction (line of action) Sense (pushes or pulls along the line of action) Force is known as a vector Mathematical representation of anything described by size or direction MISSAM Mechanical Dept. LJ Polytechnic
  6. 6. INTRODUCTION WHAT ARE FORCES MISSAM Mechanical Dept. LJ Polytechnic
  7. 7. CLASSIFY FORCES INTERNAL FORCES Forces that act within the object or system whose motion is being investigated Muscles pull on tendons, which pull on bones At joints, bones push on cartilage Tensile forces—Pulling forces acting on the ends of an internal structure Compressive forces—Pushing forces acting on the ends of an internal structure MISSAM Mechanical Dept. LJ Polytechnic
  8. 8. CLASSIFY FORCES INTERNAL FORCES Sometimes the tensile or compressive forces acting on a structure are greater than the internal forces the structure can withstand— Structure fails or breaks—Muscle pulls, tendon ruptures, ligament tears, bone breaks Muscles can only produce internal forces—They are incapable of producing changes in the motion of the body without external forces Body is only able to change its motion if it can push or pull against some external object (e.g. ground reaction force) MISSAM Mechanical Dept. LJ Polytechnic
  9. 9. CLASSIFY FORCES INTERNAL FORCES MISSAM Mechanical Dept. LJ Polytechnic
  10. 10. CLASSIFY FORCES EXTERNAL FORCES MISSAM Mechanical Dept. LJ Polytechnic Forces that act on an object as a result of its interaction with the environment Non-Contact forces—Objects not touching (e.g. gravity, magnetic, electrical)—Gravity is primarily studied in sports biomechanics Gravity (g) accelerates objects downward at 9.81m/s2 no matter how large or small the object, and any place on earth (ignoring air resistance) MISSAM Mechanical Dept. LJ Polytechnic
  11. 11. CLASSIFY FORCES EXTERNAL FORCES MISSAM Mechanical Dept. LJ Polytechnic Weight—In biomechanics, force of gravity acting on an object— Don’t confuse with weight as commonly thought of being in lbs from a bathroom scale W = mg W = weight (measured in N) m = mass (measured in kg) g = acceleration due to gravity How much do you weigh?
  12. 12. CLASSIFY FORCES EXTERNAL FORCES DIPAK SIR Mechanical Dept. LJ Polytechnic Contact forces—Occur between objects in contact with each other Objects in contact can be solid or fluid (e.g. air resistance and water resistance are fluid) Forces between solid objects studied primarily in sports biomechanics—An athlete and some other object (opponent, ground, implement) To put a shot, an athlete must be holding the shot To jump up, an athlete must be in contact with the ground and push down To run forward, an athlete must push backward against ground
  13. 13. CLASSIFY FORCES EXTERNAL FORCES DIPAK SIR Mechanical Dept. LJ Polytechnic
  14. 14. KINEMATICS and KINETICS INTRODUCTION DIPAK SIR Mechanical Dept. LJ Polytechnic  KINEMATICS: It deals with the Bodies in motion without any reference to the forces which are responsible for the motion.  Description of motion - change in position Cars sports: baseball, football, soccer, etc. world: rotates and revolves KINETICS: It deals with the Bodies in motion due to application of force.
  15. 15. SCALAR and VECTOR QUANTITIES INTRODUCTION DIPAK SIR Mechanical Dept. LJ Polytechnic  SCALAR QUANTITIES: A scalar quantity is one which can be completely specified by it’s magnitude only.  Example: Length Mass Time Distance VECTOR QUANTITIES: A vector quantity is one which can be completely specified by it’s magnitude and direction.  Example: Displacement Velocity ,Acceleration
  16. 16. INTRODUCTION COMPLETED MISSAM Mechanical Dept. LJ Polytechnic THANK YOU

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