physics grade 8

1. Conditions Of Equilibrium Of
A Body
Done By : Doaa Al Mahdawi
Salah Al Sary

2. ‫وصلت‬ ‫إن‬
،ً‫ا‬ّ‫ي‬‫ح‬ ،‫البيت‬ ‫إلى‬
‫القافية‬ ‫تصل‬ ‫كما‬
،ٍ‫ل‬‫خل‬ ‫بال‬
‫لنفسك‬ ْ‫ل‬ُ‫ق‬:ً‫ا‬‫شكر‬!
ً‫ا‬‫شيئ‬ َ‫عت‬َّ‫توق‬ ‫إن‬
ً‫ا‬‫غد‬ ‫حدسك،فاذهب‬ ‫وخانك‬
،َ‫نت‬ُ‫ك‬ ‫أين‬ ‫لترى‬
‫للفراشة‬ ْ‫ل‬ُ‫وق‬:ً‫ا‬‫شكر‬!
ٍ‫ة‬‫ورد‬ ‫إلى‬ َ‫نظرت‬ ‫إن‬
ْ‫توجعك‬ ‫أن‬ ‫دون‬
،‫بها‬ َ‫وفرحت‬
‫لقلبك‬ ‫قل‬:ً‫ا‬‫شكر‬!
‫اسمك‬ ‫من‬ ً‫ا‬‫حرف‬ ‫تذكرت‬ ‫إن‬
،‫بالدك‬ ‫واسم‬
ً‫ا‬‫طيب‬ ً‫ا‬‫ولد‬ ‫كن‬!
‫الرب‬ ‫لك‬ ‫يقول‬ ‫كي‬:ً‫ا‬‫شكر‬!
‫درويش‬ ‫محمود‬

3. Forces
Main Objectives:
•To define the Force.
•To characterize the Force.
•To distinguish between the different types of the Forces.
•To deduce the conditions of equilibrium of two forces.

4. Definition of the Force:
A force is a mechanical action that may set a body in motion
or modify its motion or modify its shape.
Pulling

5. Characteristics of Force:
•Its point of application: is the center of gravity of the body or point of
contact.
•Its line of action: vertical, horizontal or oblique.
•Its direction: (upward- downward), (to the right, to the left), (upward to
the right, downward to the right, upward to the left, downward to the left).
•Magnitude: Its numerical value in the SI unit Newton (N)

6. Measurement of Force:
•A force is measured using spring balance.
•Its SI unit is Newton symbolized by N.
• A force is represented by force vector (convenient scale
must be chosen to draw F).

7. Types of Force:
•Forces acting from a distance ex: magnetic force, electric
force and gravitational force.
•Contact force ex: normal, pushing pulling, tension…

8. Particular Forces:
The weight:
• The weight of a body is force acting from a distance exerted by the
earth on the object. It is also called the force of gravity.
The characteristics of weight:
• Its point of application: the center of gravity of the body.
• Its line of action: vertical.
• Its direction: downward.
• Magnitude: W = m × g.

9. Normal: It is a force exerted by a surface on a body. It is a contact force.
To find the characteristics of normal:
• Its point of application: point of contact.
• Its line of action: vertical
• Its direction: upward.
• Magnitude: ------

10. Tension: It is a force exerted by a spring or string on a body. It is a contact force.
To find the characteristics of tension:
• Its point of application: point of contact.
• Its line of action: vertical
• Its direction: upward
• Magnitude: T= k × ∆x

11. Force of friction: It is a force due to the sliding (motion) of a body. It
is a contact force.
To find the characteristics of friction:
• Its point of application: point of contact.
• Its line of action: along the line of motion.
• Its direction: opposite to the motion.
• Magnitude : -----

12. Equilibrium of a body:

13. Equilibrium of a body:
When a body is in equilibrium then the two forces have:
•Same line of action
•Opposite direction
•Same magnitude

14. Exercise I:
( S)
A box (S) of mass 1kg is suspended to the free end of a spring
as shown in the figure.
Take g=10N/Kg.
•Name the forces acting on solid (S).
•Calculate the weight of (S).
•Deduce the following characteristics of a force exerted by a spring on (S):
a. Line of action .
b. Direction .
c. Magnitude .

15. DONE