Simple Machines
Levers
Objectives
You will be able to…
…explain what a lever is.
…distinguish between the different parts of a
lever.
…describe the difference between a 1st, 2nd,
and 3rd Class Lever.
…explain the difference between Mechanical
Advantage and Disadvantage.
…calculate the Ideal and Actual Mechanical
Advantage, Velocity Ratio and Efficiency of
a lever.
What is a Lever?
All levers are made up of 4 components:
LOAD
FULCRUM
EFFORT
LEVER ARM
Parts of a Lever
EFFORT
LOAD
FULCRUM
LEVER ARM
If
theE
F
ULCRUM
isthe
The
LOAD
EVER
is a
L
F
ULCRUM
FFORT
isAthe
isRM
isan
located
atthat
the
rigid
bar
rests
on
weight
pivot
outside
point
of
force
the
or(person,
moment
midpoint
of
the
and
rotates
about
the
object(s)
around
machine,
which
that
natural
isthebeing
L
EVER ARM
and theItto
F
ULCRUM
. It, applied
serves
moved
forces
phenonoma)
rotate.
(displaced).
E
FFORT the
is equal
toof
transfer
represents
to
the lever.
aforce
Itforce
is also
that
the
L
OAD, then
the
the
EFFORT
the
is measured
measured
intoin
pounds
lever
be perfectly
L
OADwill
. (lbs)
pounds
(lbs).
balanced.
Advantages of Levers:
… can be used to change the direction of
an applied force (EFFORT)
… can increase or decrease an applied
force
… can increase or decrease the distance
travelled by an object (LOAD)
150 lbs
Your muscles
When
Imagine
weyou
lift are
heavyproduce
trying
must
to
objects,
lift a an
box
we
mustweighs
that
upward
produce
force150
of
an
upward
lbs.
150
lbs or
force
more
that
in
is equal
order
to to
raise
or the
greater
box
to the
than
desired
the
150 lbs
weight of that
height.
object.
For example...
If your
Your
muscles
muscles
must produce
cannot
produceanthe
upward force
necessary
upward
of
150 lbs
force
to or
overcome
more in
order
the
weight
to raise
of the
box to
box,
then
the desired
height. can
problems
occur.
Levers can help!
Classes
of
Levers
st
1
Class Levers
In a 1st Class Lever, the FULCRUM is
located between the LOAD and the EFFORT.
LOAD
EFFORT
FULCRUM
st Class
Note
In
a 1that
the forces
Lever, of
thethe
FULCRUM
LOAD and
is the
located
E
FFORT between
are moving
the in
LOAD
the same
and the
direction.
EFFORT.
EFFORT
LOAD
FULCRUM
EFFORT
FULCRUM
LOAD
Homemade Lift
When the FULCRUM is moved to one side,
mechanical advantage or disadvantage
occurs.
EFFORT
Note:
EFFORT
LOAD
smaller EFFORT,
but greater distance
OAD
that it must move
L
FULCRUM
Other examples of 1st Class Levers...
Tongs
Other examples of 1st Class Levers...
Paint Can Opener
nd
2
Class Levers
In a 2nd Class Lever, the LOAD is located
between the FULCRUM and the EFFORT.
LOAD
FULCRUM
EFFORT
Note that the forces from the LOAD and the
EFFORT are pointing in opposite directions.
LOAD
FULCRUM
EFFORT
EFFORT
FULCRUM
LOAD
Bottle Opener
Other examples of 2nd Class Levers...
Wheelbarrow
Other examples of 2nd Class Levers...
Nut Cracker
A 2nd Class Lever always has mechanical
advantage.
LOAD
FULCRUM
EFFORT
rd
3
Class Levers
In a 3rd Class Lever, the EFFORT is located
between the FULCRUM and the LOAD.
LOAD
FULCRUM
EFFORT
As was the case with the 2nd Class Lever, the
forces from the LOAD and the EFFORT are
pointing in opposite directions.
LOAD
FULCRUM
EFFORT
Unlike the class 2 lever, a 3rd Class Lever has
mechanical disadvantage. The EFFORT must
be greater than the force of the LOAD.
LOAD
FULCRUM
EFFORT
However, the distance moved by the
LOAD is greater than the distance moved
by the EFFORT.
LOAD
FULCRUM
EFFORT
EFFORT
LOAD
FULCRUM
Human Arm
Other examples of 3rd Class Levers...
Shovel
Other examples of 3rd Class Levers...
Tweezers
Levers
in
Combination
EFFORT
FULCRUM
LOAD
Lever #1 = 2nd Class Lever
Nail Clippers
EFFORT
FULCRUM
LOAD
Lever #1 = 2nd Class Lever
Lever #2 = 3rd Class Lever
Nail Clippers
Levers
&
Mathematics
Moment:
The tendency to produce motion around
an axis or point.
The turning effect produced by a lever
is called a moment. It is the product of
the applied force and the distance of
that force from the fulcrum.
Moment = force x distance = Work
1st Class Lever
EFFORT
20 lbs
force x distance = Moment = Work
20 lbs x 5 ft = 100 (EFFORT Moment) = 100 Joules
1st Class Lever
LOAD
force x distance = Moment = Work
50 lbs x 2 ft = 100 (LOAD Moment) = Joules 50 lbs
1st Class Lever
EFFORT
LOAD
20 lbs
EFFORT Moment = LOAD Moment
Balanced Lever
50 lbs
Ideal Mechanical Advantage:
…IMA
…also known as Theoretical Mechanical Advantage (TMA)
…the ratio between the EFFORT-arm length to the
LOAD-arm length.
IMA =
rE
rL
IMA =
5
2
2.5 : 1
6 in.
0.75 in.
IMA =
rE
rL
6
IMA =
.75
=8
or
ratio 8 : 1
IMA =
rE
rL
2
IMA =
20
= 0.1 or ratio 0.1 : 1
2 in.
20 in.
Actual Mechanical Advantage:
…AMA
…the ratio between the force applied to the LOAD
arm and the force applied to the EFFORT arm
AMA =
EFFORT
FL
FE
LOAD
20 lbs
AMA = 50
20
= 2.5 or ratio 2.5 : 1
50 lbs
Efficiency:
…(Greek
lowercase H…pronounced Eta)
…the ratio of AMA to IMA
…friction at the FULCRUM will cause the AMA to
be less than the IMA, resulting in an efficiency
less than 1
Efficiency =  =
AMA
IMA