Download The Science of “Punkin` Chunkin`”

The Science of “Punkin’ Chunkin’”
The first World Championship Punkin’ Chunkin’
Festival took place in 1986, in Bridgeville,
Delaware. Three “pumpkin chunking” machines
entered in the contest, with the winning shot
launching a pumpkin 114 feet. By 2009, the
festival had grown to include 115 teams of
pumpkin chunkers. The winning team launched
one pumpkin a whopping 4,480 feet.
Direction of a Force
At first glance, slinging a pumpkin through the
air to see whose goes the farthest seems like
nothing more than a little autumn enjoyment.
Like so many games, however, more than a little
science lies behind the fun.
Is there science behind this smashed
pumpkin?
Newton’s laws describe the motion of objects
when the objects are acted upon by forces. The first of Newton’s
laws states that objects at rest will stay at rest and objects in
motion will stay in motion, unless acted upon by a force. This
tendency of objects is called "inertia." In pumpkin terms, a
pumpkin at rest will stay at rest unless a force acts upon it. In a
pumpkin chunkin’ contest, teams build a variety of machines
that exert a force on a pumpkin to cause
the pumpkin to move. Newton’s second
law tells us that the direction of an
object’s motion is determined by the
direction of the net force acting on the
object. Therefore, a pumpkin flies in the
direction of the net force exerted on it.
Pumpkins as Projectiles
Regardless of the type of machine teams
use to fling their pumpkins, once the
pumpkins are airborne, they are
considered projectiles. A projectile is an
Archery is one of many sports that depends on
object that moves as a result of its own
the motion of a projectile.
inertia and the force of gravity. An arrow
released from a bow is an example of a projectile. The
pumpkin’s inertia causes it to go in a straight path from the
point at which it was released from the machine. The force of
gravity pulls down on the pumpkin. This causes the pumpkin to
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The Science of “Punkin’ Chunkin’”
gradually become lower and lower, and the resulting
motion is a curved line that arcs toward the ground.
Pumpkin Slingshot
The pumpkin slingshot works like the typical Yshaped slingshot. These pumpkin-slinging devices
often consist of a long elastic band attached to two
poles. Participants in the pumpkin chunking contest
place the pumpkin in the center of the elastic band
and pull back as far as they can then let go. With
A slingshot transforms elastic
these devices, two factors affect how far and in
potential energy to kinetic
energy—energy of motion.
which direction the pumpkin will go. According to
Newton’s laws, the amount and direction of the
force applied to the pumpkin determine the pumpkin's direction
and speed. The amount of force depends on how far a person
can stretch the elastic band. Slingshots change potential energy
to kinetic energy. The type of potential energy stored in a
stretched elastic band is called elastic potential energy. The
farther the band is stretched, the more potential energy is stored
up. When the band is released, that potential energy becomes
kinetic energy, or energy of motion.
To make sure a pumpkin projectile goes as far
as possible, its direction matters as well. Pulling
down and back on the elastic band will cause
the pumpkin to fly in a slightly upward
direction. This helps the pumpkin travel a
longer distance before gravity pulls it to the
ground.
Pumpkin Catapult
A projectile will travel farther if it is shot
at an upward angle.
For the World Championship Punkin’
Chunkin’ Festival, more detailed machines are
often built. One common machine used in competitions is a
trebuchet catapult. Like a slingshot, a trebuchet catapult relies
on the transformation of potential energy to kinetic energy.
However, the trebuchet uses gravitational potential energy
instead of elastic potential energy from a stretched elastic band.
The trebuchet is a lever with a long arm and a short arm. A
heavy weight is attached to the shorter arm. The pumpkin is
loaded into a sling at the end of the longer arm. Remember that
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The Science of “Punkin’ Chunkin’”
an object has gravitational potential
energy because of the pull of gravity
on the object. Therefore, potential
energy increases as height increases.
Also, massive objects have greater
gravitational potential energy than
smaller objects. This is because the
pull of gravity is greater on larger
objects. In a trebuchet, the heavy
weight has a large amount of
potential energy due to its position
above Earth’s surface. When the
weight drops, potential energy
changes to kinetic energy. This
provides the force needed to project
the pumpkin into the air.
A trebuchet uses the gravitational potential energy of
a heavy weight.
The amount of force the trebuchet can create depends on many
factors, including the mass of the weight, the height of the
fulcrum, and the length of the arms. When a force moves an
object around a pivot point—in this case the fulcrum of the
lever—the result is known as torque. Torque is the amount of
force that produces rotational motion, or force that moves an
object around a pivot or axis. In order to win a pumpkin
chunkin’ contest with a trebuchet, teams try to build a machine
that provides the most torque. Maximizing the torque usually
involves a heavy weight very close to the fulcrum of the
machine, and a relatively long arm attached to a holder for the
pumpkin.
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