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Chapter 4: Statics

(نوﻛﺳﻟا مﻠﻋ)

Torques and Equilibrium

Torques and Equilibrium

(نازﺗﻻا و موزﻌﻟا)


Outline

? Torques (موزﻌﻟا)

? Equilibrium of Rigid Bodies

ﺔﺑﻠﺻﻟا

ﺔﺋﺳﺎﺟﻟا مﺎﺳﺟﻻا نزاوﺗ

-

(

)

? The Center of Gravity (لﻘﺛﻟا زﻛرﻣ)

The Center of Gravity (لﻘﺛﻟا زﻛرﻣ)

? Stability and Balance (نزاوﺗﻟا و رارﻘﺗﺳﻻا)

? Levers; Mechanical Advantage

ﺔﯾﻟﻻا ةدﺋﺎﻔﻟا

ﻊﻓاورﻟا

(

:

)

? Muscles (تﻼﺿﻌﻟا)

? Levers in the Body (ﺔﯾﺣﻟا تﺎﻧﺋﺎﻛﻟا مﺳﺟ ﻲﻓ ﻊﻓاورﻟا)


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 (كﻔﻟا),

? Biological structures : Jaws (كﻔﻟا),

limbs(فارطا), or backbones(يرﺎﻘﻔﻟا دوﻣﻌﻟا).

? Engineering, comparative anatomy( ﺢﯾرﺷﺗ

نرﺎﻘﻣ), physical therapy(

ﻲﻌﯾﺑط

ﻟا جﻼﻌﻟا

), and

orthodonture (نﺎﻧﺳﻻا مﯾوﻘﺗ).






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

? Unlike most of the other muscles in our

bodies, the masseter muscle(ﺔﻐﺿﺎﻣﻟا ﺔﻠﺿﻌﻟا) in

the jaw, as illustrated in next slide, is

attached relatively far from the joint, enabling

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.










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

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

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.




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?

(a) What class of lever does this represent?

Class 1

(b) The anterior muscles (ﺔﯾﻣﺎﻣﻻا تﻼﺿﻌﻟا)produce

forward motions of the head. What class of

levers does their action represent? Class 3


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