Introduction to Statics

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Introduction to Statics
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Statics is the branch of mechanics concerned with
the analysis of loads (forces, torque/moment) on
physical systems in static equilibrium . . . when
in static equilibrium, a system is either at
rest, or its center of mass moves at constant
velocity. Wikipedia.org
old railroad bridge (Leonard G. / Wikipedia)

• ENGR 122

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Units of Measure
Most units of measure can be broken down into the
basic units of length (L), mass (M) and time (t).
physical quantity dimension SI system U.S. Customary system
length
area
volume
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Units of Measure
physical quantity dimension SI system U.S. Customary system




L length M mass ttime
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Three Characteristics of a Force

• Magnitude (F)
• how hard you are pushing or pulling
• graphically represented by the length of the arrow

• Direction (q)
• usually defined by an angle measured relative to
  a coordinate system

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Components of a Force
Forces can be split into components that align
with a coordinate system. The force is the vector
sum of the components.
y
 
 
 
 
 
q
 
x
 
defined relative to the x axis in this case
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Resultants
How can we find the net effect of two or more
forces that act on a body?
 
 
 
 
Geometric Solution If all applied forces are
arranged head to tail, a vector drawn from the
tail of the first vector to the head of the last
vector represents the resultant of all the forces.
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Class Problem Two ants are hitched to a beetle
and pull with the forces shown

• Find the x and y components of the force exerted
  by ant 1.
• Find the x and y components of the force exerted
  by ant 2.
• Find the x component of the resultant force of
  the ants.
• Find the y component of the resultant force of
  the ants.
• Find the resultant force of the ants.
• What angle does the resultant force make
• with the x-axis?