THE STUDY OF HOW A CATAPULT LAUNCHES VARIOUS PROJECTILES
Jack Haldane
Cary Academy
ABSTRACT
The purpose of this study was to test the catapult’s accuracy by shooting it at a target. This will
explain the catapult’s accuracy when launches at moving objects. The method was to see how
many catches a person could get when they stood at different distances. The results were more
catches were made at 5 m than any other distance. This is because the farther away a person was
the easier it is for a person to aim the projectile at them and for them to catch it because their
eyes can track it more easily because it is coming in slower from farther away.
INTRODUCTION
This paper will describe the physical and scientific properties of the ancient medieval weapon,
the catapult. This project looks at how a catapult works, and launches. A catapult is a device that
uses accumulated tension that is released to throw a projectile some distance. There are three
different types of catapults; the ballista, the traditional catapult and the trebuchet. The ballista is
a large crossbow, the catapult is an arm that launches a projectile, and a trebuchet is a heavy
beam that swings a sling carrying the object. Any type of catapult stores tension in some way
then releases it to launch an object. The four questions were gravity, projectile motion, what is a
catapult, and what experiments have been done on a catapult before. Gravity is the driving force
behind all matter; and projectile motion is a three-dimensional motion. A catapult is a simple
machine that uses gravity and projectile motion to launch an object into space. Some
experiments that have been done before are the maximum distance of a projectile when weights
were added on to it. The catapult was the first weapon invented to repel invaders because it could
shoot huge objects very far. The same technology from the catapult is used in surface to air
missiles and rocket launchers.
Figure 1: A model of a catapult.
Gravity is the driving force behind all matter. Gravity pulls together all matter, and binds it.
Relating to the catapult, though gravity allows it to shoot a projectile up into the air. This is
because gravity pushes objects, such as the projectile to the ground. Without gravity, every
object would be floating into space. Gravity is the reason why the planets orbit the sun. This is
because the sun has the most gravity, pulling all of the planets toward it in an everlasting circle.
Gravity is also what allows the projectile to go into the air and then sink down. When the arm of
the catapult is released, and the projectile goes into the air, gravity acts upon it and pushes it to
the ground. This is because gravity attracts objects to the center of the earth. Gravity is one of the
four fundamental forces of nature. Gravitation or gravity is a power of attraction that acts
between and on every physical object with substance (mass) or energy. When a meteorite, or a
piece of space junk strikes earth, it is pulled into earth’s field of gravity, instantly making it crash
to the ground. Gravity is the only force acting upon mass.
Projectile motion is a three-dimensional motion. There are two different motions, horizontal and
vertical motion. Vertical motion is when an object is thrown down, and if a person were to throw
the object up, it would not land in the same place as before. Horizontal motion is when an object
or a projectile is thrown forward. A projectile is another name for a parabola. If a projectile was
to be thrown using horizontal motion, it would go farther than the place that it was thrown from,
versus if a person were to throw an object using vertical motion, the projectile would go straight
up in the air and land exactly or close to where it was thrown. The reason why projectile motion
is a 3-D motion instead of a one dimensional motion is because a 1-D motion would be to throw
the projectile in a straight line, and a 3-D motion would be to throw it at a curved angle. Another
term that affects projectile motion is trajectory. Trajectory is the path of a projectile as it flies
through the air. Trajectory also determines the angle at which the projectile was thrown.
Trajectory is affected by gravity when gravity is pushing the object or projectile down when
trajectory is guiding its path.
A catapult is a simple machine that uses gravity and projectile motion to launch an object into
space. It was first used in ancient times by different armies using the catapults to knock down
castle walls. Nowadays, catapults are not used, but the science behind the catapult was used to
develop more recent products, like the satellite guided missile launchers. A catapult is used when
the arm of a catapult is pulled back and gravity acts upon it, pushing it down. Then using
projectile motion, the arm flings upward and trajectory guides it up into space. A catapult is
made of wood, string, a projectile, and nails. A catapult was better for invading castles than a
crossbow because it could shoot from farther away and still hit its target. The romans modified
the early catapult, calling it a ballista and improving the strength. Catapults were first invented in
400 B.C. by the romans. Early catapults were not that accurate, but could shoot far distances.
Around the same time era, the crossbow was invented for accuracy.
Figure 2: Demonstrating how a catapult launches.
There have been many experiments done on catapults. One of them included testing the
maximum distance of a projectile based on how much weight was added to the projectile. This
person wanted to know what projectile would fly the farthest. He tested books and play-doh. The
play- doh turned out to launch the farthest. Another experiment tested how different weights
affect the launch distance in catapults. They took a 45o and the length of the sling the same; they
added weights as projectiles to see which one would launch the farthest. They found out that the
heaver the weight, the shorter distance it goes.
MATERIALS AND METHODS
Here are the materials that were used in the experiments; a catapult, a golf ball, meter sticks, a
rubber ball, a tennis ball, a green plastic ball, a whiffle ball, many test subjects, and a protractor.
For the first experiment, the method was to see how many turns it would take to launch the
projectile (a green plastic ball). Tension was created by turning the pegs one 3600 rotation. The
catapult would then be aligned with the meter sticks. The minimum amount of turns to launch
the projectile was nine. It was then tested at 9, 10, 11, 12, and 13 turns. There were 3 tries for
each turn rotation. It was measured were the projectile first made contact with the ground.
For the second experiment, the method was to see how many catches a test subject could get
when a projectile (a green plastic ball) was launched at them. The catapult was set to 13 turns.
Test subjects would get 5 tries for each m. They were tested at 2 m, 3 m, 4 m, and 5 m. It was
measured were the projectile first made contact with the ground.
For the third experiment, the method was to see how far different types of balls launch. There
was the green plastic ball, a golf ball, a tennis ball, a rubber ball, and a whiffle ball. Meter sticks
were placed in front of the catapult to measure the distance that each ball launched. The catapult
was set to 13 turns. It was measured were the projectile first made contact with the ground.
For the fourth experiment, the method was to see how far a projectile launches at different
angles. The catapult was set to 13 turns. Meter sticks were placed in front of the catapult to
measure the distance that the projectile went. It was measured were the projectile first made
contact with the ground. The angles that were measured were 0, 15, 30, 45, and 60. 3 tries were
done on each angle and then the average was found of those tries.
Four different experiments were completed using the catapult. The experiments were testing
distance using torsion, accuracy, angle of trajectory, and different projectiles. Distance was
tested by increasing the torsion on the catapult by tightening the arm of the catapult. Accuracy
was tested by shooting a projectile at a person, and seeing how many times they could catch it
out of five tries per m. Angle of trajectory was tested by pulling the arm of the catapult back at
certain angles using a protractor, and then launching it to see how far it would go based on the
angle. Using different projectiles was tested by taking five different projectiles and launching
them at the same angle and measuring the distance.
RESULTS AND DISSCUSION
1200
1000
Distance launched
800
600
400
200
0
0
2
4
6
8
10
12
14
# of turns
Figure 3: Determining the number of turns it takes to launch a projectile.
At 13 turns the catapult was found to launch the farthest (956.7 cm). When the tension in the
catapult was wound down, it launched objects at lesser distances. At 12 turns it launched
813.3cm, at 11 turns it launched 606.7 cm, at 10 turns it launched 550 cm, and at 9 turns it
launched 458 cm. Over all it was found that if the tension in the catapult is increased, the farther
the projectile goes.
4
3.5
# of catches
3
2.5
2
1.5
1
0.5
0
0
1
2
3
4
5
6
distance flown (m)
Figure 4: Determining the number of catches at different distances.
It was determined that the father away a person is from the catapult, the easier it is to catch it.
The optimal launching angle for a person to catch a projectile with the catapult is 13 turns at 0
degrees. The closer in a person got to the catapult; the harder it was for them to catch it. This is
because it was harder for the catapult to aim at them because the projectile would seem like it
was going by faster because they were in close versus being farther away, and the projectile
seems to come at them slower.
600
distance (cm)
500
400
300
200
100
0
green ball
golf ball
rubber ball
type of ball
Figure 5: How far different types of balls launch.
wiffle ball
tennis ball
The whiffle ball proved to launch the farthest because of its light weight. The whiffle ball
launched at 485 cm. The tennis ball went the least distance because of its greater mass (62.2
cm). The green plastic ball went 467.3 cm, the rubber ball went 185cm, and the golf ball went
313.7 cm. Overall it was found that the lighter and smaller mass of the ball, the farther it went
versus if the projectile had a larger mass and was heavier, it went slower and covered less
distance then the lighter projectiles.
450
400
distance (cm)
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
70
angle of trajectory (deg)
Figure 6: How a projectile launches at different angles.
It was found that at 30 degrees the projectile launched the farthest (411.3 cm). That makes 30
degrees the optimal launching angle for the catapult. At 0 degrees it launched 321.7 cm, at 15
degrees it launched 328.3 cm, at 45 degrees it launched 293.3cm, and at 60 degrees it launched
193.3 cm. in conclusion it was found that 30 degrees was the best angle to launch the projectile
at.
CONCLUSION
The most important experiment that was done was to see the optimal distance at a set angle and a
set number of turns to catch the projectile. The hypothesis was wrong because it was predicted
that the closer in the person was, the easier it would be to catch the projectile. The results were
important to the world because this shows the world how people in medieval times used
catapults and how they shot those catapults based on the accuracy testing that was done in the
second experiment. Some future experiments that could be done off of this would be a test on a
baseball players arm when he launches the ball, and see if that angle is the same as the optimal
launching angle on the catapult because they both use similar physics.
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