3. Did you know that pliers, scissors, and the
crowbar are examples of a lever? A lever
is a simple bar that can rotate about a
point called a fulcrum.
4. Do you know that certain parts of human act as
levers?
5. Levers are force multipliers as well as distance
multipliers. In pliers, a small force handle produces a large force
at the jaw. In the human arm, a small movement of a muscle
causes a large movement of the hand. Some levers also change
the direction of the force applied.
6. A lever is a machine consisting of a beam or rigid rod pivoted at a
fixed hinge, or fulcrum. It is one of the six simple machines is identified
by Renaissance scientists. The word comes from the French lever, "to
raise". A lever amplifies an input force to provide a greater output force,
which is said to provide leverage. The ratio of the output force to the
input force is the ideal mechanical advantage of the lever.
7. Classes of levers
Levers are classified by the relative positions of
the fulcrum and the input and output forces. It is
common to call the input force the effort and the output
force the load or the resistance. This allows the
identification of three classes of levers by the relative
locations of the fulcrum, the resistance and the effort:
8. Class 1: Fulcrum in the
middle: the effort is applied
on one side of the fulcrum
and the resistance on the
other side, for example,
a crowbar or a pair of
scissors.
9. Class 2: Resistance in the middle: the
effort is applied on one side of the
resistance and the fulcrum is located on
the other side, for example, a
wheelbarrow or a nutcracker or a bottle
opener.
10. Class 3: Effort in the middle:
the resistance is on one side
of the effort and the fulcrum
is located on the other side,
for example, a pair
of tweezers or the human
mandible.
11. The mechanical advantage for various levers can be calculated
by measuring the force applied and the force produced using the
equations previously given. The mechanical advantage can also be
calculated by measuring the effort arm ( the distance from the fulcrum
to the effort, De) and the resistance arm (the distance from the
fulcrum to the resistance, Dr). This is the theoretical mechanical
advantage.
12. It will be good to remember as well some properties of MA for
the different type of levers.
First-class levers (fulcrum between the forces)
MA can be <1,= 1, or >1.
Second-class levers (resistance force between effort force and
fulcrum): MA always >1.
Third-class levers (effort force between resistance and
fulcrum): MA always <1.
13. Look at the system below. A load of 30N is supported by a 10
N effort. What is its mechanical advantage
15. It was Archimedes that
mathematically formulated lever and pulley
idea of mechanical advantage by the Use of
the Gravitational phenomena
Archimedes was a Greek who was born in
Syracuse, Sicily circa 287 B.C..He used
some of his idea for making war machinery.
He was the first to invent calculus. He also
discovered and formulated the law of
Gravitational buoyancy.
Who discovered Lever and Pulley?
16. A law which applies Universally to any medium.
Archimedes would be the One who officially used the scientific
method of experimentation. He is famous for the phrase "Eureka!"
Even though any one in primitive culture with any amount of
intelligence had already figured out the Scientific method, way before
him.
18. What is the minimum force that is required to lift the load with
a force acting on it of 300N?
19. Firstly the moments must be equal on both sides of the
fulcrum at the point where the load force just balance the effort force.
So the minimum force required to just lift the load is 60N
20. What is the maximum force that is required to lift the load
with a force acting on it of 300N?
21. Firstly the moments must be equal on both sides of the fulcrum at the point
where the load force just balance the effort force.
So the maximum force that can be opposed with a force of 300N is 900N.
What is the maximum force that is required to lift the load with a force
acting on it of 300N?
