living with the lab
Introduction to Statics
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
living with the lab
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
2
living with the lab
Units of Measure
physical
quantity
L = length
dimension
M = mass
SI system
U.S. Customary
system
t=time
3
living with the lab
Three Characteristics of a Force
denotes a vector
y
1. Magnitude (F)
•
•
how hard you are pushing or pulling
graphically represented by the length of
the arrow
2. Direction (q)
•
q
usually defined by an angle measured
relative to a coordinate system
3. Point of Application
x
4
living with the lab
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
5
living with the lab
Resultants
How can we find the net effect of two or more forces that act on a body?
Generally . . .
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.
6
living with the lab
Class Problem: Two ants are hitched to a beetle and pull with the forces shown:
a.
b.
c.
d.
e.
f.
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?
7