Chapter4: Statics - Torques and equilibrium


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Chapter Four: Statics

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Chapter4: Statics - Torques and equilibrium

  1. 1. Chapter 4: Statics (‫)علم السكون‬ Torques and Equilibrium (‫)العزوم و التزان‬
  2. 2. Outline  Torques (‫)العزوم‬  Equilibrium of Rigid Bodies (‫) توازن الجسام الجاسئة-الصلبة‬ Center of Gravity (‫)مركز الثقل‬  Stability and Balance (‫)الستقرار و التوازن‬  Levers; Mechanical Advantage (‫)الروافع: الفائدة اللية‬  Muscles (‫)العضلت‬  Levers in the Body (‫الروافع في جسم الكائنات‬ ‫)الحية‬  The
  3. 3. Introduction  Statics is the study of the forces acting on an object that is in equilibrium and at rest.  Engineering structures: Bridges or buildings  Biological structures : Jaws (‫,)الفك‬ limbs(‫ ,)اطراف‬or backbones(‫.)العمود الفقاري‬  Engineering, comparative anatomy(‫تشريح‬ ‫ ,)مقارن‬physical therapy(‫ ,)العلج الطبيعي‬and orthodonture (‫.)تقويم السنان‬
  4. 4. Torques
  5. 5. Torque
  6. 6. Examples
  7. 7. Conditions for a rigid body equilibrium:
  8. 8. Types of equilibrium:  static equilibrium: a state of equilibrium in which the net external force and torque acting on a system is zero  dynamic equilibrium: a state of equilibrium in which the net external force and torque on a system moving with constant velocity are zero
  9. 9. Example
  10. 10. Example 2
  11. 11. Stability and Balance
  12. 12. Example  Unlike most of the other muscles in our bodies, the masseter muscle(‫)العضلة الماضغة‬ in the jaw, as illustrated in next slide, is attached relatively far from the joint, enabling large forces to be exerted by the back teeth. (a) Using the information in the figure, calculate the force exerted by the teeth on the bullet. (b) Calculate the force on the joint.
  13. 13. A person clenching a bullet between his teeth
  14. 14. Solution
  15. 15. Lever in Human Body
  16. 16. Lever in Human Body
  17. 17. Lever in Human Body
  18. 18. Lever in Human Body
  19. 19. Lever in Human Body
  20. 20. Lever in Human Body
  21. 21. Glossary  torque: turning or twisting effectiveness of a force  perpendicular lever arm: the shortest distance from the pivot point to the line along which F lies  SI units of torque: newton times meters, usually written as N·m  center of gravity: the point where the total weight of the body is assumed to be concentrated
  22. 22. Exercise 4-13  Find the force F1 and F2 on the tooth in fig. 4.36 (In orthodonture, forces applied to the teeth lead to forces on the supporting bones, Gradually the bone tissue breaks down and permits the tooth to rotate or translate. New bone tissue grows in the space left behind. The forces must be small enough to avoid damaging the root of the tooth.
  23. 23. Solution
  24. 24. Exercise 37  The head pivots about the atlanto-occipital joint (Fig.4.46). The splenius muscles attached behind the joint support the head. (a) What class of lever does this represent? Class 1 (b) The anterior muscles (‫)العضلت المامية‬produce forward motions of the head. What class of levers does their action represent? Class 3