Mechanism
Bilingual Section
Ies Pedro de Valdivia
Author: Juan Carlos Parejo Reja
Voice and reviced by:
Elisabeth Kate Orchard
Mechanism
• A lever is a simple machine that makes work easier for
use; it involves moving a load around a pivot using a
force. In a lever there is a load, a pivot and an Effort
(force). Levers are amongst the oldest form of
mechanical system.
Levers
• The input of this
system is called the
effort and the output
is called the load. In
the image, we have
the input as F1 and
the output as F2.
The bar pivots on a
fixed point
(fulcrum).
Levers
• The principle of the lever
tells us that the lever is
in static equilibrium, with
all forces balancing, if
F1D1 = F2D2.
• In order to lift a bigger
load (L1) the distance to
the fulcrum has to
increase (D2) or the
distance D1 has to
decrease.
First Class Lever
• First Class Lever
– With this type of
lever the fulcrum
is situated
between the load
and the applied
force
Second Class Lever
• Second Class
Lever
– With this type of
lever the load is
situated between
the fulcrum and
the applied force.
Third Class Lever
• Third Class Lever
– With this type of
lever the force is
applied between
the load and the
fulcrum.
Exercices
• 1º You need to lift a load of 200 kg (F1). The
distance from the load to the pivot(D1) is 6
meters and the distance from the pivot to
• where the force is applied (D2) is 20 meters.
Calculate the value of F1.
Exercices
• 2º On the lever showed in the image D1 =
20, D2 = 400 and F1 = 300 Kg. Calculate
the value of F2
• 3º On the same image, calculate the value of
D1 if D2 = 70m, F1 = 300Kg and F2 = 60kg
Exercices
• Write the lever class of every object
Pulley
• A pulley is a
wheel with a
groove along its
edge, for holding
a rope or cable.
Pulleys
• Pulleys are usually used to reduce the
amount of force needed to lift a load.
However, the same amount of work is
necessary for the load to reach the
same height as would be necessary
without the pulleys. The magnitude of
the force is reduced, but it must act
over a longer distance
Types of pulleys
• 1º Fixed: A fixed
pulley has a fixed
axle. That is, the
axle is ""fixed"" or
anchored in a place (
maybe the roof, ..).
A fixed pulley is used
to redirect the force
in a rope A fixed
pulley has a
mechanical advantage
of 1
•
1. mechanical advantage (MA) is
the factor by which a mechanism
multiplies the force put into it
Types of pulleys
• 2º Movable: A movable
pulley has a free axle.
That is, the axle is "free"
to move in space. A
movable pulley is used to
transform forces. A
movable pulley has a
mechanical advantage of 2.
Types of pulleys
• 3º Compound A compound pulley is a
combination of fixed and movable pulley
systems. The simplest theory of
operation for a pulley system assumes
that the pulleys and ropes are
weightless, and that there is no energy
loss due to friction. It is also assumed
that the ropes do not stretch.
compound pulley
• 1º A basic equation
for a pulley: In
equilibrium, the
force F on the pulley
axle is equal and
opposite to the sum
of the tensions in
each line leaving the
pulley, and these
tensions are equal.
compound pulley
• Example 2 - A simple
pulley system - a
single movable pulley
lifting a unit weight.
The tension in each
line is half the unit
weight and an
advantage of 2.
compound pulley
• Example 3 - Another
simple pulley system
similar to example 2,
but in which the
lifting force is
redirected downward.
compound pulley
• A practical
compound pulley
Exercices:
• Calculate the
advantage of this
pulley system
compound pulley
• Example 4 - A simple
compound pulley
system - a movable
pulley and a fixed
pulley lifting a unit
weight. The tension
in each line is one
third the unit weight
compound pulley
• Example 5 - a
movable pulley and a
fixed pulley lifting a
unit weight, with an
additional pulley
redirecting the lifting
force downward. The
tension in each line is
one third the unit
weight.
• Which is its M.A?
compound pulley
• Example 6 - A
more complicated
compound pulley
system. The
tension in each
line is one quarter
of the unit
weight. It has an
advantage of 4.
Gear
• Gears or toothed
wheels are type
drives which are used
to transmit motion
between two shafts
or a shaft and a
component having
linear motion, by
meshing of two or
more gears.
Gear
• The ratio of the
rotational speeds
of two meshed
gears is called the
Gear ratio.
Worm Gear
• If you want to create a
high gear ratio, nothing
beats the worm gear. In a
worm gear, a threaded
shaft engages the teeth on
a gear. Each time the
shaft spins one revolution,
the gear moves one tooth
forward. If the gear has
60 teeth, you have a 60:1
gear ratio in a very small
package. Here is one
example
Gear
Exercices. What is
the output in
revolutions per
minute at Gear C?
Gear
Exercices. Gear A
revolves at
90revs/min. What
is the output and
direction at Gear
C.
Gear
Exercices. Calculate the
output speed (the
speed at which the
blue gear move) if:
V1= 3000 (Orange gear)
and t1=20 teeth
T2 = 50 teeth
T3 = 200 teeth
Compounds Gears
In a compound gear, all gears
are fixed on the same axel
moving at the same speed.
This is an example of a
“compound gear train”.
Gear A rotates in a
clockwise direction at 30
revs/min. What is the
output in revs/min at D and
what is the direction of
rotation ?
GEAR
A
GEAR
B
GEAR
C
GEAR
D
120 T
40 T
80 T
20 T
Gear and belt
The advantages of
chains and belts are
light weight, the
ability to separate the
two gears by some
distance, and the
ability to connect
many gears together
on the same chain or
belt
Gear and belt
In this image, you
can see some
toothed belt to
connect the axil
motor to other
componets of the
car engine
Pulley systems
The diagram shows a
small driver pulley ( on
the left) pulling round
a larger driven pulley.
The rpm (revolutions
per minute) of the
larger driven pulley
wheel will be less than
the smaller driver
pulley wheel.
Pulley systems
Pulley systems are used
when there is a need to
transmit rotary motion..
It is a simple mechanical
device to winch up and
down a rope. When the
motor is turned on it
revolves the driver pulley
wheel. The belt causes
the driven pulley wheel to
rotate as well, winding
out the rope.
Gear wheels and chains
Everyone has used a bicycle
and noticed that it is
driven by a large driver
gear wheel (pedal gear)
with pedals attached.
Smaller gears at the back
are driven round, in turn
driving round the back
wheel. As the back wheel
turns the bicycle moves
forwards. Gears driven by
chains are used in
motorcycles, in car engines
, etc.
Rack and pinion
The rack and pinion
gear system allows
rotary motion of
the steering wheel
to be converted to
linear motion.
Rack and pinion
The diagram shows a
vehicle
and
its
steering system. This
allows the steering
wheel to turn the
wheels left and right
so that it can be
steered.
Crank-connecting rod
• A Crankconnecting-rod is a
Mechanism for
transformation of
rectilineal motion
in rotatory
one and vice
versa.
Crankshaft
The crankshaft( in red),
sometimes casually
abbreviated to crank,
is the part of an
engine which
translates
reciprocating linear
piston motion into
rotation.
See more about the
engine here
Cam and follower
system
A cam and follower
system is a mechanism
that uses a cam ( blue
piece) and follower to
create a specific
motion. The cam is in
most cases merely a
flat piece of metal
that has a specific
shape.