So what's a catapult?
The goal of a catapult is to fling a mass into the
air - mainly to inflict damage.
What is a Catapult?
● A catapult is a mechanical device used to store potential
energy, then release it as kinetic energy as it throws a
projectile a great distance.This is done without the aid of
● The word 'Catapult' comes from the two Greek words:
kata: downward and pultos: a small circular battle shield.
● Katapultos (Catapult) then means “shield piercer”
History of Catapults
Humans have limitations! We
can only lift so much, can only
throw so high...
History of Catapults
By increasing the energy stored in projectiles,
you can increase the amount of damage they
History of Catapults
War has always been a motivating force in
development of new technologies.
This helped engineering advance in many
areas, not just weaponry.
History of Catapults
Engineers researched ways to increase these
forms of energy storage in weapons in order
to increase their damage.
History of the catapult
In 399 BC Dionysius of Syracuse created a
think tank to design and build weapons for his
campaign against Carthage.
The goal was to overcome limitations of the
basic bow and arrow - how could they increase
the energy stored?
Who Invented the Catapult? (3rd c. BCE)
● Ancient Greek mathematician
Archimedes (b. 287 BCE) is credited with
inventing the catapult along with other
“war machines” (Death Ray, the Iron
Claw, and Steam Cannon).
● Archimedes developed the
fundamental principles of mechanics;
and methods for finding the center of
gravity, surface area, and volume of
geometric figures. He also derived an
estimate for the value of Pi. (Can we
● War has always been a motivating force in development
of new technologies.
● An interesting thing about catapults is that they
developed over time from smaller weapons.
● The Catapult is a derivative and direct result of the Bow.
● The catapult is the end result of the desire to make
weapons that are bigger, more powerful, and can
hurl bigger objects longer distances.
Types of Catapults
Catapults can be split into three categories:
● Traditional Catapult
A traditional catapult looks like a bucket on a long arm
being held down by some form of tension. These were
used into medieval times.
The traditional catapult uses
stored elastic energy (potential
energy) by twisting and
stretching ropes and in the bent
wooden arm used to vault its
mass into the air. Think about
bending a spoon back to launch
peas across the table!
Forms of Energy
● Potential energy
(stored) is energy
when matter is still.
● Kinetic energy is
matter in motion.
A traditional catapult can store more energy to
send their projectile further by using a winch.
The winch is
a wheel and
A winch allows a
person to store a great
amount of energy (in
this case, tension) over
a period of time
Ballistas and other
machines were the
A ballista looks like
a giant crossbow.
So to increase the potential energy...
● Heft the projectile higher off the ground
● Make the projectile heavier
How do these forces store energy?
Imagine a loose rubberband vs. a taut one.
Potential energy is stored in rubberband,
just like how potential energy is stored in
bow when bow is drawn.
Bow and arrow
As you pull the string of a bow, your arm does
The energy that it takes you to pull that string is
stored in the bow as tension.
Bow and arrow
When arrow is released, elastic energy
transfers to the kinetic energy of the arrow
Bow makers discovered they could strengthen
the bow even more if they combined:
● Animal horn
● & Animal sinew
Horn holds up better to
compression so was
added to the inside of a
wooden bow while
sinew holds up better to
tension so was added
to the outside
Now limitations are physiological - meaning
humans were limited by their own bodies
Can you think of what they might be?
● Length of an archer’s arms
● Strength of arm, chest, & shoulder muscles
● Strength and dexterity of fingers
Because of these limitations, the best possible
bow required 45 pounds to pull with a 28 inch
Back to the think tank...
So how was the group going to advance bow
and arrow technology?
Their first solution was the gastraphetes or
Stiffer bows made
cocking the weapon
A windlass was
added to the back of
the weapon to draw
the arrow back.
While this allowed for
larger arrows, now the
entire weapon needed
to grow in size, making
it unwieldy as a hand
held weapon. A base
Bows on this first
model of catapult
were maxing out the
size that artisans
could make them.
Composite bow temporarily meets its limits.
Developers must now turn to fundamentally different
ways of storing elastic energy.
This path led to the Torsion Catapult.
Torsion catapult development occurs over a series of
discoveries and advancements, starting in mid 4th
By end of that century we have the arrow shooting
weapon called the euthyntone and the stone
throwing weapon called the palintone.
Much of the hardware
looks the same: stock,
rachet, trigger, windlass,
What’s new are vertically
aligned torsion springs.
Torsion is the twisting of a beam
or structural element
Torsion springs in a palintone consisted of bundles of
rope with a wooden arm thrust through the center.
What material do you think was used for this rope?
Think back to when we talked about materials that could
withstand compression or tension.
The gastraphetes (`belly-bow´) was invented about 400 BC and is
considered the first mechanical weapon. It was cocked by resting
the stomach on the stock and pressing down.
The military effect of this weapon during the siege of Motya (Sicily)
397 BC encouraged the Greek engineers to develop a larger
gastraphetes, mounted on a carriage with a windlass to cock it.
...and we finally get our traditional catapult!
Physical limits prevented further enlargement of
the composite bow. In the mid-fourth
century BC torsion springs, made from
horse-hair or sinew, replaced the bow. Such
a spring could be enlarged indefinitely.
Inscriptions on the Acropolis of Athens first
mention torsion spring catapults there about
330 BC and Alexander the Great employed
them on his campaigns.
The Greeks used two types: the euthytonon for
shooting arrows and the palintonon for
throwing stone balls.
These war engines are better known today by
their Roman name: the ballista.
The onager (wild donkey), was a torsion
engine similar to the ballista but only
one arm. This catapult was the largest
weapon used by the Roman army,
almost exclusively for siege warfare.
In the 6th
century AD, the Chinese developed a large-
scale stave sling with a crew that pulled the pole.
Known today as a traction trebuchet.
Trebuchet was the ultimate achievement in mechanical
Developed in the Far East and brought west in the 10th
century by the Mongol and Muslim armies.
Trebuchet in Europe
European armies encounter and adopt the trebuchet during
the Crusades of the 12th
Siege of Jerusalem
Casting a dead horse into a besieged town
(from Il Codice Atlantico, Leonardo da Vinci)
During medieval times,
siege machines were the
first weapons used for
The carcasses of
diseased animals and
those who had perished
from the Black Death
were thrown over castle
walls to infect those
The mangonel is a simplified
trebuchet using a fixed
Decline of the Trebuchet
In this siege scene,
taken from a 14th
century document, a
behind the weapon
that would ultimately
replace it, the
Return of the Trebuchet
Many modern reproductions of
trebuchets exist today.
The trebuchet in Denmark’s Medieval
Center is built of oak and medieval
craft techniques were used in its
Has a ballast of 15 tons and is
designed to throw projectiles of up
to 300 kg.
Counterweight lifted by human powered “hamster wheels”
1. NEVER launch at people, animals, or things of value
2. ONLY use these with supervision!
3. Ask for help using potentially harmful tools, like a
knife, hot glue gun, wire cutter, or electric drill
4. Anyone aiming at others, doing stupid thing will be
Day 2….. Let’s Build An Easy One
● 9 popsicle sticks
● 7 rubber bands
● 1 bottle cap
● 1 marshmallow/pom for ammo
● Hot glue gun
What other version can you make?
● Must fit within 8 x 8 inch square
● Use only what you need
● If you don’t plan on keeping item please
leave behind to be recycled
● Respectful of space and materials
Change these factors and
see how they affect catapult