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Chapter Four: Statics
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Chapter 4: Statics ( السكون (علم
Torques and Equilibrium
( االتزان و (العزوم
Outline
Torques (العزوم) Equilibrium of Rigid Bodies
( - الصلبة الجاسئة االجسام ( توازن The Center of Gravity ( الثقل (مركز Stability and Balance ( التوازن و (االستقرار Levers; Mechanical Advantage
( االلية: الفائدة (الروافع Muscles (العضالت) Levers in the Body ( الكائنات جسم في الروافع(الحية
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(اطراف), or backbones( الفقاري .(العمود Engineering, comparative anatomy( تشريح)physical therapy ,(مقارن ال طبيعيالعالج ), and orthodonture ( االسنان .(تقويم
Torques
Torque
Examples
Conditions for a rigid body equilibrium:
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
Example
Example 2
Stability and Balance
Example
Unlike most of the other muscles in our bodies, the masseter muscle( الماضغة (العضلةin 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.
A person clenching a bullet between his teeth
Solution
Lever in Human Body
Lever in Human Body
Lever in Human Body
Lever in Human Body
Lever in Human Body
Lever in Human Body
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
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.
Solution
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 ( العضالت .produce forward motions of the head(االماميةWhat class of levers does their action represent? Class 3
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