Engr Intro to Engineering by benbenzhou

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									Lecture 10: Statics

ENGR 101: INTRO TO ENGINEERING
MECHANICS

   Mechanics is the study of the effects of forces
    acting on bodies
     Rigid bodies (statics & dynamics)
     Deformable bodies

     Fluids
STATICS

   When a body is acted upon by a balanced force
    system, the body will remain at rest or move
    with a constant velocity, creating a condition
    called equilibrium
DYNAMICS

 The study of unbalanced forces on a body
  creating an acceleration
 Newton’s second law of motion (F=ma)
SCALARS & VECTORS

   Scalar is a physical quantity having magnitude
    but no direction.
     Mass,   length, time, and temperature
   Vector has both magnitude and direction
     Displacement,velocity, acceleration, and force
     Represented by an arrow (line of action)
VECTOR



         40 N

                D




     C
FORCES

   Newton’s Third Law states that if a body P acts
    upon another body Q with a force of a given
    magnitude and direction, then body Q will react
    upon P with a force of equal magnitude but
    opposite direction
FORCE SYSTEMS

   Collinear forces:
     Magnitude    can be added or subtracted
   Concurrent forces:
     Forces   that pass through the same point in space
   Coplanar forces:
     Forces   that lie on same plane
RESOLUTION OF FORCES

 If a force is determined, then its magnitude
  direction, and one point on the line of action
  are known.
 When calculating a force, it is convenient to
  divide or resolve the force into two or more
  components (e.g. x & y direction)
RESOLUTION OF FORCES

   Fx = Fcos θ
   Fy = Fsin θ
   F = Fx2  Fy2
   Θ = tan-1 Fy/Fx

   Graphical representation
PROBLEM

   Force vector F has a magnitude of 6.50 x
    102 lb and acts through point A at a slope
    of 2 vertical to 5 horizontal. Determine
    the x and y components of F.

                            Fy              F




                                 θ
                             A
                                       Fx
    RESULTANT FORCES
   As the number of force vectors within a two-dimensional
    system increases, the complexity of the problem dictates
    that an orderly procedure be followed.
   ΣFx = Rx
   ΣFy = Ry

   R=     Rx2  Ry
                  2




   Θ = tan-1 Ry/Rx
   Watch direction!!
EXAMPLE
    Given the two-dimensional, concurrent,
     coplanar force system illustrated,
     determine the resultant, R, of the system
                      y
                                       F1=86 N


         F2=58 N                   30.0°         x


                          4

                              2
                                  F3=72 N
RESOLUTION IN 3-D

   Find the components on the x, y, and z-axis.

   Example 18.1b, pg. 466
HW

   18.1. 18.2 (pg. 470)
LIGHT LAB
 Create a robot that can sense a light bulb and
  travel within a 6-inch radius of the light source
 Robots and light source will be on opposite
  extremes of the classroom
       Obstacles will be placed in between the robot and the
        light source
   All robots are required to use at least one light
    sensor
       No cost limitation
 Robot due end of class Monday, Nov. 15th
 Full lab write-up due Wednesday, Nov. 17th

								
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