UNIT 6.Machines and mechanisms
Vocabulary
Cam
/kæm/
leva
pendulum
Crank-handle
/kræŋk-hændl/
manivela
Pulley
Crank-shaft
Kræŋk- /ʃɑ:ft/
cigúeñal
Rack and pinion
/ræk&pinion
Piñóncremallera
cylinder
/sɪlɪndəʳ/
cilindro
Ramp
/ræmp/
rampa
fulcro
Reciprocating
[rɪsɪprəkeɪti
alternativo
hidraúlica
resistance
/rɪ’zɪstəns/
resistencia
fulcrum
hydraulics
/haɪ’drɒlɪk/
/’pendjʊləm/
péndulo
polea
Lever
/livəʳ/
palanca
Rod-crank
/rɒd/- /kræŋk/
Biela- manivela
Linear
[lɪnɪər]
lineal
Rotary
/’rəʊtərɪ/
rotativo
Machine
/mə’ʃi:n/
máquina
Screw
/skru:/
tornillo
Mechanisms
/mekənizəm/
mecanismos
Shaft
/ʃɑ:ft/
eje
Motion
/məʊʃən/
movimiento
Thread
/θred/
hilo
movement
/mu:vmənt/
movimiento
Wedge
/wedʒ/
cuña
Nut
na:t
tuerca
Wheel
/wi:l/
rueda
Technology Department IES ArabuleilaCúllar Vega Granada
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Machines and mechanisms
1. Machines.
2. Mechanisms.
3. Levers.
4. The inclined plane and wheel.
a. Lever elements
b. Types of levers
c. Mechanical advantage.
d. The lever law.
5. La polea.
6. Los sistemas de transmisión circular.
7. La relación de transmisión.
8. Mechanisms for transforming the motion.
1. Machines
1.1 Machine definition
There are many types of machines and it is not easy to find a
definition that fits-all. However all of them have some common
features:
They need power to operate. This energy
can be electrical, chemical, mechanical or
otherwise.
They convert the energy they receive
into
another
type
or
types
of
energy.Usually the operation of a machine
produces
more
than
one
energy
transformation.
Produce effects. move, sound, crushed,
pushed, off heat.
Have
been
manufactured.With
one
intention: to facilitate a task, reducing the
effort required to perform a job.
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1.2 Types of machines
There are many different ways to classify machines.
According to the technology they use. Machines
can be electrical, mechanical, hydraulic. Most
machines combine several technologies.
Depending on the number of steps they need to
perform their function. They can be simple or compound
Depending on the number of parts and the difficulty of
their installation. They can be simple or complex.
1.3 Simple machines and compound machines.
Simple machines. These do the work in one step.
Essentially there are three: pulley, inclined plane and
the lever.
Compound machines. They need to connect several steps to
perform their function. Compound machines are built by
combining two or more simple machines
2. Mechanisms.
2.1 Movements on a machine
Machine movements might be complex. However all movements can be
achieved by combining four basic movements.
Linear: in a straight line that goes in one direction.
Rotary: circular motion in one direction.
Reciprocating:in a straight line, but one that continually
changes direction, which produces continuous forward and
reverse movements.
Swinging or Pendulum: a forward and backward motion that
forms an arc.
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2.2 Mechanisms
Machine movements have to be precise. To achieve this we use
mechanisms.
Mechanisms are used to:

Transmit movements and forces from one point to another of
a machine, as do the levers, pulleys and gears.
 Transform movements, changing speed, direction, or type of
movement. For example, making a circular motion into a
linear, as is the case of nut and screw mechanism.
 Steer, regulate and control the movements
3. Levers.
A lever is a rigid beam that can rotate around a fixed point on
which it is supported.
3. 1 Lever elements
A lever has the following elements:
The power or force applied.
The resistance that we have to overcome.
The support point or fulcrum.
The power arm, which is the distance between the fulcrum
and the point where the power is applied.
The resistance arm, which is the distance between the
fulcrum and the point where the resistance is located.
3. 2Types of levers
Depending on how the elements of a lever are
applied, there are three types of levers.
First-class lever. Has the power at
one end, the resistance at the other,
and the fulcrum is between these two.
Second-class lever. Has the fulcrum at
one end, applying power at the other,
the resistance is between both.
Third-class lever. Has the fulcrum at
one end, the resistance at the other,
the power is applied between both.
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3. 3 Combinations of levers
These can combine two or more levers to work together, for
example scissors, forceps and nutcrackers are combinations of
two levers that share the same fulcrum.
3. 4 The mechanical advantage
When power applied is smaller than the resistance to overcome,
we say that there is a mechanical advantage, because we have
managed to multiply force.
The mechanical advantage is the
between the resistance and power.
mathematical
relationship
To have mechanical advantage, the power arm must be longer than
the resistance arm. The longer the power arm and the smaller the
resistance arm, the lower the effort.
3. 5
The lever law
For a lever to be balanced, so as not to rotate, it must meet
the following equation:
Power x Power arm = Resistance x Resistance arm
4. The inclined plane and wheel
These two machines are based on the same principle as the lever:
a small force applied over a long distance has the same effect
as a large force applied over a small distance.
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4.1
The inclined plane
The inclined plane or ramp is a machine that can be used to lift
objects with less effort. The longer the ramp the less effort
required.
The wedge is the union of two inclined
planes for their supports. It is used for
separating and cutting.
The screw is a special type of inclined plane. Consists of
a cylinder or cone which is surrounded by a ramp HELIX
called thread.
4.2
Wheel
A wheel consists of a round body (cylinder or disk) which
rotates about an axis or integrally with it. Applying a force on
the edge generates a much larger force in the shaft. This force
will be greater the larger the radius of the wheel.
The mechanical advantage is dependent on the radius of the shaft
and the wheel.
8. Mechanisms for transforming the motion.
The input motion is different from the output motion.
8.1
Circular – linear transformation
a. screw and nut:
This consist of a screw and a nut, one
of which is fixed and the other
movable.
It's able to transform a rotary motion
in lineal one, with a great speed reduction and
therefore with greatly increased strength.
b. Rack and pinion
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Consists of a sprocket (pinion) which is crimped
to a toothed bar (zipper). The rack advances and
retreats by the rotation of the pinion.
c. Cam
This mechanism consists of an axis
that rotates, the cam can be a more or
less eccentric wheel, and the follower
is moved by being pushing by the cam
when it rotates.
8.2
Circular-alternative transformation
d. Crank handle and crank shaft
A crank handle is a rigid rod bent at a right
angle.
A crank shaft is a set of crank handles mounted on
the same axis.
e. Rod-crank
A rod is a rigid bar, that
connects
a
rotating
body
by
articulated
joints
to
another
which performs a reciprocating
movement.
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