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Figure 1-14.-A. A pelican hook; B. A chain stopper. | Up
Basic Machines - Intro to machines and motion theories | Next
Chapter 2 Block and Tackle |
SUMMARY
Now for a brief summary of levers:
Levers are machines because they help you to do
your work. They help by changing the size,
direction, or speed of the force you apply.
There are three classes of levers. They differ
primarily in the relative points where effort is
applied, where the resistance is overcome, and
where the fulcrum is located.
First-class levers have the effort and the resistance
on opposite sides of the fulcrum, and effort and
resistance move in opposite directions.
Second-class levers have the effort and the
resistance on the same side of the fulrum but
the effort is farther from the fulcrum than is the
resistance. Both effort and resistance move in
the same direction.
Third-class levers have the effort applied on the
same side of the fulcrum as the resistance but
the effort is applied between the resistance and
the fulcrum, and both effort and resistance
move in the same direction.
First- and second-class levers magnify the amount
of effort exerted and decrease the speed of
effort. First-class and third-class levers magnify
the distance and the speed of the effort exerted
and decrease its magnitude.
The same general formula applies to all three types
of levers:
L
R
— = —
l
E
Mechanical advantage (M.A.) is an expression of
the ratio of the applied force and the resistance.
It may be written:
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