A. Spring
Helical extension springs appear to be similar to
compression springs, having a series of coils
wrapped into a cylindrical form. However, in
extension springs, the coils either touch or are closely
spaced under the no-load condition. Then as the
external tensile load is applied, the coils separate.
The drawbar spring incorporates a standard helical
compression spring with two looped wire devices
inserted through the inside of the spring. With such a
design, a tensile force can be exerted by pulling on
the loops while still placing the spring in compression.
A torsion spring, as the name implies, is used to exert
a torque as the spring is deflected by rotation about
its axis.
Leaf springs are made from one or more flat strips of
brass, bronze, steel, or other materials loaded as
cantilevers or simple beams. They can provide a
push or a pull force as they are deflected from their
free condition.
A Belleville spring has the shape of a shallow, conical
disk with a central hole. It is sometimes called a
Belleville washer because its appearance is similar to
that of a flat washer. A very high spring rate or spring
force can be developed in a small axial space with
such springs
Garter springs are coiled wires formed
into a continuous ring shape so that
they exert a radial force around the
periphery of the object to which they
are applied.
Constant-force springs take the form of
a coiled strip. The force required to pull
the strip off the coil is virtually constant
over a long length of pull. The
magnitude of the force is dependent on
the width, thickness, and radius of
curvature of the coil and on the elastic
modulus of the spring material.
Power springs, sometimes called motor
or clock springs, are made from flat
spring steel stock, wound into a spiral
shape. A torque is exerted by the spring
as it tends to unwrap the spiral.
v.
B. Simple Stresses
i.
ii.
iii.
iv.
Tensile Stress is the ratio of a stretching force
acting on a material to the cross-sectional
area of that material. It is the force per unit
area that is putting an object in tension.
Compressive Stress - Compressive means
the material is under compression and that
there are forces acting on it trying to
compress the material.
Bearing stress is the contact pressure
between the separate bodies. It differs from
compressive stress, as it is an internal stress
caused by compressive forces.
Shear Stress - A type of stress that acts
coplanar with cross section of material.
vi.
Bending/Flexure Stress is the internal
resistance generated within a component
when an external bending moment or force is
applied.
Torsional Stress is a form of shear stress
experienced by a body when a twisting force
is applied.
C. Thin-Walled Cylinder
i.
ii.
iii.
ii.
Tangential Stress (Circumferential Stress)
Longitudinal Stress
Spherical Cylinders
iii.
D. Kinematics
i.
ii.
iii.
iv.
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vii.
viii.
MECHANICS – deals with the relations
among force, matter, and motion.
KINEMATICS – the part of mechanics
concerned with describing motion.
MOTION – is a continuous change of
position.
VELOCITY - The velocity of a body is a
vector quantity that describes both how
fast it is moving and the direction in which
it is headed. The magnitude of a velocity
is sometimes called speed.
ACCELERATION - The acceleration of a
body is the rate at which its velocity is
changing.
- Acceleration is the second
derivative of displacement.
AVERAGE ACCELERATION - The
average acceleration of the particle as it
moves from a point to another is defined
as the ratio of the change in velocity to the
elapsed time.
INSTANTANEOUS ACCELERATION - The
instantaneous acceleration of a body is its
acceleration at some one instant of time or
at some one point of its path.
Projectile motion is the motion of an object
thrown or projected into the air, subject to
only the acceleration of gravity. The object
is called a projectile, and its path is called
its trajectory.
E. Newton’s Law of Motion
i.
FIRST LAW OF MOTION
A body at rest will remain at rest, and a
body in motion will continue to move with
constant velocity if there is no force acting on
it.
ii.
SECOND LAW OF MOTION
If a net force F acts on an object of
mass m, the object will have acceleration a.
iii.
THIRD LAW OF MOTION
To every action there
opposed and equal reaction.
iv.
is
always
CENTRIPETAL FORCE
is a net force that acts on an object to
keep it moving along a circular path.
v.
ROTATION
F. Oscillation and Simple Harmonic Motion
i.
Oscillation is defined as the process of
repeating variations of any quantity or
measure about its equilibrium value in time.
iv.
v.
vi.
vii.
viii.
ix.
Vibration is used to describe the
mechanical oscillations of an object. A
particle being vibrated means it oscillate
between two points about its central point.
Sine wave is a perfect example of
oscillation. Here the wave moves between
two points about a central value.
Amplitude (A) is the height or the maximum
distance that the oscillation takes place
Period (T) is the time taken to complete one
complete cycle
Frequency (F) is the number of complete
cycles that occur in a second. Frequency is
the reciprocal of the time period.
Restoring Force - when an elastic object
such as a spring is stretched or
compressed, a restoring force appears that
tries to return the object to its normal
length.
Hooke's Law - the restoring force Fr is
proportional to the displacement x provided
the elastic limit is not exceeded.
Simple Harmonic Motion is periodic motion
that occurs when the restoring force on a
body displaced from an equilibrium position
is proportional to the displacement and in
the opposite direction.