Fascinating Science of the Trebuchet

The Trebuchet is an intriguing medieval device for flinging rocks and other projectiles.  It differs from a catapult insofar as it does not use torsion or bending, neither the bending of wood (such as a bow or ballista) nor the torsion of twisted ropes (often seen in Roman catapults).  It can be built on huge scales to heave heavy boulders and other massive projectiles.

The Trebuchet Store has a good basic summary of 

How a Trebuchet Works

They also provide an good animated drawing of a hinged counter-weight trebuchet in action:

Perhaps the best way to get to know the trebuchet (considered the most powerful medieval siege engine) is to build one yourself.  There are many kits available.  A free one that you can make using print-outs on card stock is available from 

Fryer's Kits

One to purchase inexpensively (compared to some kits!) which I have built and can recommend is 

 Pathfinder Hinged Counter-Weight Trebuchet

 

The Pathfinder Trebuchet under construction.  At this point I had glued and pegged together the frame and base as well as the counter-weight box which will eventually be filled with stones.  The pegging is done for added strength.  At this point the building instructions say to stop and have a snack!

And now the completed model on the dining room floor with special guest star William Shakespeare to suggest the approximate human scale:

And in another close-up picture:

From the dining room floor I was able to hurl a grape into the kitchen, a distance of about 20 feet or 6 meters.

Here is a fun video of a family using the Pathfinder trebuchet on their back deck (and includes a helpful warning about the dangers of standing directly behind the trebuchet):  

Once constructed you can make some adjustments to try and get the maximum firing range.  You can add or remove stones from the counter-weight box.  You can change the length of the string that runs from the sling pouch (that holds the grape) to the top of the throwing arm.  

A Virtual Trebuchet is handy to see how changing these various parameters can affect the throwing.  Just set the parameters and press the SUBMIT button to fire the trebuchet:

Online Virtual Trebuchet 

My own fascination with trebuchets was inspired by the excellent article that appeared in Scientific American:

The Trebuchet

It is also helpful to watching the firing of a full scale trebuchet such as the one we watched being fired in Provence, France:

Or check out what is considered to be the world's biggest trebuchet in action at Warwick Castle:

Daily Planet documents the largest trebuchet in continental Europe and the difficult process of adjusting the firing range:

One of the reasons I started watching the great series Northern Exposure (about a young New York doctor exiled to a small Alaskan community) was that I read they had actually built a trebuchet capable of hurling an old upright piano... 

      

 

There are many interesting trebuchet videos on YouTube, including the following fascinating experimentation with both fixed and hinged counter-weights:

Trebuchets have appeared in TV shows and movies.  The Historian on the Warpath has critiqued a few.  First the Game of Thrones trebuchet that appears during the Battle of the Bastards:

Problems with the Game of Thrones Trebuchet 

The Game of Thrones trebuchet was apparently based upon an amazing trebuchet named Merlin that was actually built and fired:

 Historian on the Warpath also critiqued the Boulder Machine Gun Trebuchet that was used in the Chronicles of Narnia:

Trebuchets on Screen: Chronicles of Narnia