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Chapter 2 Notes
Mechanical Equilibrium
Mechanical Equilibrium
· Things in mechanical equilibrium are
stable, without changes in motion.
· Ex: Rope
2.1 Forces
· Force
· A push or a pull
· A force is required to change an object’s
state of motion.
· Net Force
· The combination of all forces acting on an
object
· Newton= about 0.22 lbs (1N = 2 lbs)
2.1 Forces
· Vector
· An arrow that represents the magnitude and
direction of a quantity
· When a force is represented by an arrow, the
length is scaled to represent the amount
(magnitude) of the force, and the direction
of the arrow points in the direction of the
force
2.1 Forces
· Vector Quantity
· A quantity that needs both magnitude and direction
for a complete description
· Force, velocity, acceleration
· Scalar Quantity
· A quantity that can be described by magnitude only
and has no direction
· Time, area, volume, temperature
2.2 Mechanical Equilibrium
· Mechanical Equilibrium
· Is a state wherein no physical changes occur
· A state of steadiness
· Equilibrium Rule
· Whenever the net force on an object is zero,
the object is said to be in mechanical
equilibrium
2.2 Mechanical Equilibrium
· Equilibrium Rule
· Mathematically ΣF=0
·
·
·
·
Σ stands for “the sum of”
F stands for forces
All the forces acting on an object add vectorially to zero
If up = +, then down = -
2.3 Support Forces
· Support force (Normal Force)
· For an object at rest on a horizontal surface,
the support force must equal the object’s
weight
· ΣF=0
2.4 Equilibrium for Moving
Objects
· An object moving at a constant speed in a
straight-line path is in a state of equilibrium.
· Equilibrium is a state of no change.
· Objects at rest are said to be in static
equilibrium, objects moving at constant
speed in a straight-line path are said to be in
dynamic equilibrium.
2.5 Vectors
· Combining parallel vectors
· If they are in the same direction, they add
· If they are in oposite directions, they
subtract
· Resultant
· The sum of two or more vectors
2.5 Vectors
· The Parallelogram Rule
· To find the resultant of two non-parallel
vectors, construct a parallelogram wherein
the two vectors are adjacent sides. The
diagonal of the parallelogram shows the
resultant
2.5 Vectors
· Tail to tip Method
· Place the tail of the second vector on the tip
of the first.
· (Place the tail of the next vector on the tip of the
previous.)
· A line drawn from the tail of the first to the
tip of the last is the resultant.
2.5 Vectors
· Vector Subtraction
· Vectors are subtracted by adding a vector of
the same magnitude in the opposite
direction.
· Vector Multiplication/Division
· The magnitude is changed. The direction
stays the same (unless multiplied by a
negative.)