fluid force

1. DYNAMIC : NEWTON’S LAW OF
MOTION
• Force ( Applied force, normal force, gravitational force, frictional
force)
• Newton’s First Laws of Motion
• Mass, weight
• Newton’s Second Laws of Motion
• Newton’s Third Laws of Motion.
• Free Body Diagram.
• Friction, Coefficient of friction,
• Horizontal and Inclines plane.
• Solving problem with Newton’s Law: Free Body Diagram.
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2. 2
At the end of this section, students should be able to:
LESSON OUTCOMES:
1) Define type of Force (Applied force, normal force, gravitational force, frictional
force)
• uses the equation F = ma to solve simple problems
• states that the unit of force is the newton (N)
2) Newton’s First Laws of Motion
• states Newton’s first law
3) Newton’s Second Laws of Motion.
• states Newton’s second law
4) Newton’s Third Laws of Motion.
• Free Body Diagram.
• Friction, Coefficient of friction,
• Horizontal and Inclines plane.
• Solving problem with Newton’s Law: Free Body Diagram.

3. What is a FORCE ?
• An interaction between TWO objects or
• The cause of motion (what causes objects to move)
Two method in producing forces :
3
i) Push ii) Pull
.

4. An object at rest needs a force to
get it moving; a moving object
needs a force to change its
velocity.
The magnitude of a force
can be measured using a
spring scale.
FORCE
SI Unit : Newton (N) @ kgm/s2.
Quantity : Vector
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5. • An applied force is a force that is applied to an object
by a person or another object.
• If a person is pushing a box across the room, then
there is an applied force acting upon the object.
• The applied force is the force exerted on the box by
the person.
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APPLIED FORCE, F

6. Forces may cause the object - balanced or unbalanced
• Balanced forces – all forces acting on an object are equal
– There is NO MOTION
• A net force is ZERO ( ∑F = 0 )
• Unbalanced forces – one or more forces acting on an object
are stronger than others
– There is MOTION
• A net force have value ( ∑F ≠ 0 )
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BALANCED AND UNBALANCED FORCE

7. •Arrows are used to represent forces. The length of the
arrow is proportional to the magnitude of the force.
• Net force : The vector sum of all forces acting on that
object.
Individual Forces Net Force
6 N10 N4 N
FORCE
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8. • Gravitational force or weight, W is the force exerted on that
object by gravity.
Mass is measured in kilogram (kg)
• Mass is not weight
• Direction: directly downward from the object.
Fg or W = mg
W
Gravitational Force, Fg
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9. Normal Force, FN
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• A reaction force exerted by
surface
• Cannot exist on its own
• Direction: Always
perpendicular to the surface
W
FN
object
floor
Also called reaction force.

10. Frictional Force, Ff
10
• Force that always oppose the motion of the object
• Exist at rough surface
F
Ff
Coefficient
of friction Normal Force
Nf μFF 

11. Tensional Force, FT
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• Exist at rope, cable
• Direction: always away from body
• Tension at smooth pulley (frictionless pulley)
always similar, hence FT1 = FT2
FT1
FT2

12. END OF
SLIDE
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13. 13

14. 14

15. NEWTON’S FIRST LAW
An object at rest will stay at rest, and an object in
motion will stay in motion at constant velocity,
unless acted upon by an unbalanced force.
• When no force acts on an object, F = 0, a = 0
• Also called law of inertia
• Inertia is the tendency for object to resist change in
its velocity.
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16. Mass & Inertia
• Mass is the amount of
matter in an object.
• The more MASS an
object has, the more
INERTIA the object has.
• Bigger objects are harder
to start & stop
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Which vehicle has more
inertia?

17. When the net force acting on an object is not zero, the object
will accelerate at the direction of the exerted force.
The acceleration is directly proportional to the net force and
inversely proportional to the mass.
NEWTON’S SECOND LAW
17
m
m
F
aaF

 
 ,

18. Exercise 1 : Lets try this!!
Determine the accelerations which result when a 12-N
net force is applied to a 3 kg object and then to a 6 kg
object.
Solution:
18

19. Newton’s third law:
• Whenever one object exerts a
force on a second object, the
second exerts an equal force
in the opposite direction on the
first.
 For every action, there is an
equal and opposite reaction.
NEWTON’S THIRD LAW
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20. 20

21. Free Body Diagram (FBD)
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1. For one object, draw a free-body diagram, showing all the
forces acting on the object.
2. Label each force. If there are multiple objects, draw a
separate diagram for each one.
3. Resolve vectors into components.
4. Apply Newton’s law to each component.
5. Solve.
R
W

22. 22
Exercise : Draw Free Body Diagram for figure below
a)
b)
c) Inclined plane (smooth surface)
d ) Inclined plane (rough surface)
θ
θ

23. 23
Exercise : Draw Free Body Diagram for figure below
e)
f)
g)
smooth surface
rough surface

24. Exercise 1 : Lets try this!!
Suppose the coefficient of kinetic friction is 0.05 and
the total mass is 40kg. What is the kinetic frictional
force?
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25. Solution :
25
( Ans : 19.6 N)

26. Exercise 2 : Lets try this!!
A 10.0-kg box is pulled along a horizontal surface by a
force of 40.0 N applied at a 30.0° angle above
horizontal. The coefficient of kinetic friction is 0.30.
Calculate the acceleration.
30°
26

27. Solution :
27
( Ans : 1.12 m/s2 )

28. Exercise 3 : Lets try this!!
A box of mass 10kg is placed on a smooth incline that
makes an angle 30° with the horizontal.
(a) Draw the FBD
(b) Determine the normal force on the box.
(c) Determine the box’s acceleration.
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29. Solution:
29
( Ans : 84.87 N, 4.9 m/s2 )

30. 3 kg
2 kgm1
m2
Exercise 3 : Lets try this!!
Find the acceleration of the pulley system as in the figure.
Solution:
30
( Ans 1.96 m/s2 )