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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
  • Dr. Meyassar N. Al-Haddad
  • 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
(No Transcript)
18
Review
  • Example 13.1
  • Example 13.2
  • Example 13.3
  • Example 13.4

19
Thank You
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