# 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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