Levers

Levers are one of the simple machines
that were probably used in prehistoric
times. Levers were first described about
260 BC by the ancient Greek
mathematician Archimedes (287-212
BC).
Levers

A lever is a simple machine that makes
work easier for use; it involves moving
a load around a pivot using a force.
Many of our basic tools use levers,
including scissors (2 class 1 levers),
pliers (2 class 1 levers), hammer claws
(a single class 2 lever), nut crackers (2
class 2 levers), and tongs (2 class 3
levers).
Levers

In physics, a lever is a rigid object that
is used with an appropriate fulcrum or
pivot point to multiply the mechanical
force that can be applied to another
object.
Levers

The lever allows less effort to be
expended to move an object a greater
distance.
The three classes of levers

A first-class lever is
a lever in which the
fulcrum is located in
between the input
force and the output
force.
Class 1 levers
Examples: #Seesaw (also known as a
teeter-totter)
 1. Crowbar or claw hammer (removing
nails)

2. Pliers (double lever)

The three classes of levers

In a second-class
lever the input is
located to the far
side of the bar, the
output is located in
the middle of the
bar, and the fulcrum
is located on the
side of the bar
opposite to the
input.
Class 2 Levers
#
#
#
#
#
#

Wheelbarrow
Nutcracker
Door
Pry bar
Stapler
Diving board
The three classes of levers

Class 3 levers. The
input effort is higher
than the output
load. However, also
notice that the input
effort moves
through a shorter
distance than the
output load.
The Lever Lab

To determine how levers change the
force required to move an object.
Way Cool Levers

The trebuchet is a counterweight siege
engine. Basically, a lever and a sling.
But First!………...
A bit about Siege Engines

Basically there are three ways to power
a machine that throws a projectile.
– Flexion
– Torsion
– Levers
A bit about Siege Engines

Flexion
– Which is the bending of a limb or leaf
spring.
– Bows, crossbows, and the most ancient of
large Greek rock throwing and arrow
throwing siege engines were Flexion.
– The gastrophetes was the first recorded
arrow throwing siege engine showing up
around 399 BC.
A bit about Siege Engines
A bit about Siege Engines
A bit about Siege Engines

Torsion
– They have arms similar to the limb of a
bow on a crossbow, but the arms are
independently powered by bundles of
semi-flexible sinew cord wrapped into a
frame of wood which are pretensioned and
then twisted.
– Recorded first around 250 BC.
A bit about Siege Engines
A bit about Siege Engines

The two-armed ballista and catapulta
invented by the Greeks and later used
by Romans was largely replaced by the
Roman onager, which was a much
simpler design, using only one arm to
propel a rock with a sling.
A bit about Siege Engines
A bit about Siege Engines

In the early Middle Ages, walls and
fortifications had become taller and
stronger than they ever were in ancient
Greek times, and the stone castle was
developed, which had walls stronger
than most ancient siege engines could
destroy.
A bit about Siege Engines

From the Mongolians in the east came
the idea for a new type of siege engine,
powered by gravity and designed for
one purpose; to destroy walls. This
was the trebuchet.
Trebuchet

The trebuchet is a Type-1 lever and a
sling. In the Type-1 lever, the force is
applied to one end, the load is on the
other end and the fulcrum sits between
the two.
Trebuchet

The sling is the oldest projectile
weapon. There is a pouch to hold the
projectile and two long strings. Both
ends of the string are held in one hand
and the sling is swung around and
around. Then, at the proper moment,
one end of the sling is let go with the
other end is still held by the hand
Trebuchet
Historic Counterweight Trebuchet
Illustrations
Trebuchet from The Romance of Alexander (circa 1330).
Historic Counterweight Trebuchet
Illustrations
Trebuchet by Kolderer, c1507.
Historic Counterweight Trebuchet
Illustrations
An early 14th Century trebuchet
Historic Counterweight Trebuchet
Illustrations
A 13th Century "Mongol" trebuchet
Historic Counterweight Trebuchet
Illustrations
A fixed-weight trebuchet
from the early 16th Century