# Smashing pumpkins: a fall festival gives new meaning to the phrase "food fight".

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Fourteen-year-old Brielle Hohne stands in a field among catapults and air cannons. She pulls a pin from one of the nearby contraptions, causing a wooden arm to swing upward and launch a pumpkin hundreds of feet through the air. Thousands of spectators look on as the pumpkin lands on the ground with a "Splat!"

Brielle is participating in the annual World Championship Punkin Chunkin competition outside Bridgeville, Delaware, where entrants fling pumpkins for fun and charity. She is part of an all-kid team from New Jersey that will compete this November for the fourth time. Their parents supervise, but the kids design the machine that will launch their pumpkin. "We actually put it together," Brielle says. "We just use the adults to do the stuff that we can't do, like the heavy lifting." Read on to see how the laws of physics help her team, named Prickett's Punkin Chunkers, pitch its pumpkin.

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A MACHINE WITH POTENTIAL

The machine Brielle's team has used most often over the years is a trebuchet (treb-yoo-SHAY), which uses a falling mass to throw an object (see Nuts & Bolts, below). Like a seesaw, a trebuchet has a long arm set on a fulcrum, or pivot. One end connects to a sling that holds the pumpkin. A mass is raised on the other end to create potential energy, or stored energy. When the mass on the trebuchet falls, its potential energy gets converted to kinetic energy--the energy of motion. The other end of the arm rises, whipping the sling into the air.

To maximize the distance the pumpkin flies, Brielle can adjust the location of the fulcrum. "It's about the leverage," she says. Greg Romine a scientist at the Stanford Physics Department explains: "Moving the falling weight toward the fulcrum will cause a higher launch speed of the pumpkin, but the pumpkin's mass must be lessened. Moving the weight away from the fulcrum will allow the launching of a more massive pumpkin, but at a slower launch speed."

AIRBORNE PUMPKINS

Brielle and her team use calculations based on mass, energy, and gravity to figure out how far their machine can hurl a pumpkin. The kids are well-versed in Newton's First Law of Motion. This physics principle, which states that an object in motion continues in motion unless a force acts upon it, explains why the team's pumpkin continues sailing upward after it leaves the sling. But eventually, gravity and drag between the pumpkin and the air slow the projectile.

So far, Brielle and her team's careful work has nabbed them a first, second, and third place in recent years. And everyone has a smashing good time.

web extra

See the machines in action at www.scholastic.com/scienceworld.

nuts & bolts

A TREBUCHET AT WORK

A trebuchet is a type of catapult. It uses leverage to propel a projectile, in this case, a pumpkin.

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* What is a catapult? A trebuchet?

* What physical factors do you think allow machines like a catapult or trebuchet to hurl objects farther than a person alone can?

* Would you want to enter a contest where you build your own pumpkin-launching machines? Why or why not?

DID YOU KNOW?

* The Punkin Chunkin contest has categories for tile different methods of pumpkin hurling: slingshots, catapults, trebuchets, and air cannons. If a pumpkin explodes in midair, it's called "pumpkin pie in the sky."

* The heaviest pumpkin grown in the U.S. in 2008 weighed in at 696.9 kilograms (1,536.5 pounds). But competitors in the Punkin Chunkin contest use pumpkins weighing 3.6 to 4.5 kg (8 to 10 lbs) for the adult classes; the youth competitors hurl pumpkins that are no less than 1.8 kg (4 lbs).

* The trebuchet was invented in China between the fifth and third centuries B.C.; the first catapult was an arrow-hurling machine invented in Greece around 339 B.C.

CRITICAL THINKING:

* A trebuchet uses a weight and a fulcrum to gain leverage and store enough potential energy to hurl an object. A catapult uses elastic tension (like a slingshot) to store its potential energy. What do you think the advantages and disadvantages of using these two methods would be?

CROSS-CURRICULAR CONNECTIONS:

HISTORY: The trebuchet and catapult were part of the arsenal for medieval siege warfare to attack rival castles. How would you build a castle to defend against such strong weapons? Use this Web site that has information about medieval life to figure out the best design for your castle: http://score.rims.k12.ca.us/activity/castle_builder.

RESOURCES

You can access these Web links at www. scholastic.com/scienceworld.

* Want to know all about the history of pumpkin chunking? Check out Bob Kotowski's book Pie in the Sky: The Authorized History of Punkin Chunkin', Cedar Tree Books, 2008.

* Trebuchets use levers to propel heavy objects. Check out this lesson plan about levers from Tufts University's STOMP Web site: http://stompnetwork.org/tufts/fellowresources /activity-database?sobi2Task=sobi2Details&catid= O&sobi2Id=20.

* This Web site that accompanies NOVA's "Medieval Siege" episode from its "Secrets of Lost Empires" series has trebuchet-related lesson plans, interactive games, and more: www.pbs.org/wgbh/nova/Iostempires/trebuchet.

DIRECTIONS: Match the words in the left column with the words or phrases in the right column.
```1. trebuchet                          a. pivot point
2. kinetic energy                     b. stored energy
3. Newton's First Law of Motion       c. energy of motion
4. fulcrum                            d. machine that uses a falling
mass to throw an object
5. potential energy                   e. principle that states that an
object in motion will stay in
motion unless a force acts
upon it
```