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## King Fahd University of Petroleum

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### Dr. Meyassar N. Al-Haddad. Lecture # 11. Sir Isaac Newton. 1642-1727. Proposed fundamental ... Law of inertia a body in motion will stay in motion and a body at ... – PowerPoint PPT presentation

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Title: King Fahd University of Petroleum

1
King Fahd University of Petroleum Minerals
• Mechanical Engineering
• Dynamics ME 201
• BY
• Lecture 11

2
Sir Isaac Newton 1642-1727
Proposed fundamental laws that are the basis of
modern mechanics 3 laws of motion law of
gravitation
3
Newtons laws
• Law of inertia a body in motion will stay in
motion and a body at rest will stay at rest
unless acted upon by a net external force.
• Law of force-acceleration A particle acted upon
by an unbalanced force F experiences an
acceleration a that has the same direction as the
force and a magnitude that is directly
proportional to the force
• Law of action-reaction for every action, there is
an equal and opposite reaction
mg FN
• Law of gravitation - all bodies are attracted to
one another with a force proportional to the
product of their masses and inversely
proportional to the square of the distance
between them.

4
13.2 The Equation of Motion
• Free-Body diagram (Force Diagram)
• Kinetic diagram (acceleration Diagram)

5
13.3 Equation of Motion for a System of Particles
Internal forces cancel each other
6
13.4 Equations of Motion Rectangular Coordinates
• When the net force is projected to separate
coordinate axes the Newtons second law still
holds

7
Free Body Diagram Method
• Draw each object separately
• Draw all the forces acting on that object
• Get x and y components of all the forces to
calculate the net force
• Apply Newtons second law to get acceleration
• Use the acceleration in any motion analysis and
establish a Kinetic Diagram

ma
8
Normal Frictional Force
Action-Reaction forces - mg FN

F
mg
Ff
FN
9

Static Friction ( ms )
• Static friction parallel force on the surface
when there is no relative motion between the 2
objects
• Static friction force can vary from zero to
Maximum
• The coefficient of static friction
• is material dependent.

10
Kinetic Friction ( mk )
• Kinetic friction parallel force on the surface
when there is relative motion between the 2
objects
• Kinetic friction force is always the same
• The coefficient of Kinetic friction
• is material dependent.

11
Friction (con.)
• When to use static friction or kinetic friction ?
• If the 2 objects have relative motion always
use kinetic friction
• If the calculated friction force to keep the 2
objects to stay together is greater than the
maximum static friction use kinetic friction
• Otherwise no relative motion, friction force is
smaller than Fmax use static friction

12
Spring Force
• Spring force
• k spring stiffness (N/m)
• s stretched or compressed length

s
13
Example 13-4
• m 2 kg
• y 1m
• smooth
• a ?

14
Problem
a ?
15
Example 13-5
m A 3 kg m B 5 kg From rest vB ? In 2 second
Block B
Same?should be
Block A
16
Problem

• VA ?
• 2Sc SA L
• 0 2ac aA aA -2ac

17
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18
Review
• Example 13.1
• Example 13.2
• Example 13.3
• Example 13.4

19
Thank You