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Destroy the Castle
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How Your Trebuchet Works
Wheels/No Wheels
When modern engineers first examined medieval drawings of
trebuchets, they couldn't help but notice that they often had
wheels.
Their first assumption was that the wheels were added to roll
the weapon around the landscape and to help aim it, which was
probably true in smaller machines. As modern engineers began
to reconstruct these monster machines, however, they came to
realize that they were too heavy to roll on medieval roads,
much less battlefields.
They also noticed something else: These rolling behemoths fire
appreciably farther than their stuck-in-the-mud cousins.
Modern engineers suspect that their medieval counterparts may
have observed the same thing and stayed with the wheeled
design as they built the machines larger.
Why is a trebuchet that rolls forward and back again more
stable and powerful than its cousin? Well, one of the design
flaws of the wheel-less trebuchet is its tendency to rear up
into the air as its arm begins to spin and then slam back
down. This monstrous lurch can destroy the trebuchet rather
than the castle wall.
Rolling wheels prevent the crushing lurch. Instead, energy is
more smoothly channeled into the trebuchet's arm and missile.
Wheels add power as the trebuchet rolls forward. Like a
pitcher who leans toward home plate as he hurls, the forward
motion adds velocity to the pitched weight. The rolling back
and forth of the wheeled counterweight also allows it to fall
in a straighter line, the most efficient way for a
counterweight to respond to the force of gravity.
The straight-falling counterweight is more powerful because a
straight falling counterweight results in a higher velocity at
the sling end at the moment of release. A higher velocity
results in a farther throw.
Medieval Arms Race
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NOVA Builds a Trebuchet
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Life in a Castle
Destroy the Castle
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| Updated November 2000
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