Physics In Film Blog

Physics In Film

Movies and TV shows, when done right, are great ways to entertain and tell stories. They can be fascinating avenues for experiencing some phenomena we may never actually witness in real life. They can also be ridiculous or laughably awful when scientific liberties are taken a bit too far. Join the CR4 team here in the Physics in Film blog as we explore the good, the bad, and the ugly of the science and engineering we see on the screen.

Previous in Blog: Medieval Physics - Jousting   Next in Blog: Do We Finally Get Hoverboards in 2015?
Close
Close
Close
9 comments

Medieval Physics - Siege Engines

Posted September 03, 2014 12:00 AM by cheme_wordsmithy

I don't think a blog series titled Medieval Physics would be complete without a discussion of siege engines. Siege engines were the machines that made possible attacks on castles and highly defensible fortifications. It is the simple physics behind these machines that make them what they are. Let's take a look at a few examples.

The Battering Ram

When an invading force had access to the castle gate, the battering ram was the siege weapon of choice for breaching the fortress. Battering rams allowed attackers to hit doors and gates with massive weights repeatedly, in order to break or force them open.

Battering rams typically incorporated a frame which allowed for the suspension of a large wooden log. Operators inside the structure would stand on either side of the suspended log and swing it back and forth into the target structure. Some more rudimentary rams with wheels were intended to be pushed by the operators (at speed) into the door or gate. The ram housing was usually covered to protect its occupants from arrows, stones, and other methods of bombardment from above.

The basic principle of the ram is Newton's first law, which states that an object in motion (the ram) will stay in motion unless a force (the door/gate) is acted upon it. The door must repeatedly take the force of the heavy log, weakening the door each time. When the door is too weak to stop the inertia of the ram, it will break open. Newton's second law, represented by F=ma, is demonstrated in that a larger (heavier) battery ram traveling at a higher speed will hit the door with more force.

The Onager

Onagers (also sometimes called Mangonels) are catapults that were used to bombard fortresses in Ancient Rome and the Middle Ages. They hurled large stones (sometimes laced with an combustible material and set aflame) across great distances. They could also be used as a defensive weapon against siege towers and the like.

Onagers worked using the principle of torsion. To fire, an operator would force down the firing arm held in tension by twisted ropes or a similar spring mechanism (see left) wound on a windlass (a winch). At full extension, the bucket or sling of the arm would be loaded with the projectile. When released from tension, the arm would swing forward, hitting a padded stop as the projectile was released. Firing distance and power were based solely on the construction of the onager, with variables including size and length of the arm and tension of the spring mechanism.

The Trebuchet

The trebuchet was the most fearsome of catapult technology used in ancient and medieval history. Trebuchets utilized the principle of counterweights to propel extremely large objects hundreds to thousands of feet at high speeds. The effect was devastating to enemy defenses and forces.

The mechanics of the trebuchet are different than the onager but equally straightforward - just imagine a see-saw (a really really big see-saw) with a menacing object sitting in a sling at one end. When a heavyweight (or force) is applied at the other end, the arm with the object will swing up at speed. As it hits a stopping point, the menacing object will be released from the sling, remaining in motion until impact with its target. The momentum transferred into the sling adds to the force of the release. Positioning the fulcrum closer to the side applying the force allows the object to be projected farther, but requires more force application and puts more strain on the lever.

If you want a very good visual example of the mechanics of these machines, check out the battle of Minas Tirith in the fantasy film The Lord of the Rings: The Return of the King.

In fact, that movie battle includes the use of not just of trebuchets, but of onagers, ladders, siege towers, and a battering ram. In the Middle Ages, some attackers would also use fiery weapons to melt the cement holding the stone construction together, or they would mine underneath the structure to destroy its foundation… the possibilities were many. Looking at the engineering and physics behind these things gives me a better understanding and appreciation of the scale and complexity of Medieval technology.

Sources:

stormthecastle.com

real-world-physics-problems.com

Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
3
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#1

Re: Medieval Physics - Siege Engines

09/04/2014 6:55 AM

The person who did the "twisted rope" picture was an artist, not a mechanic!!! It would not have worked as shown!!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply Good Answer (Score 3)
Active Contributor

Join Date: Jul 2013
Posts: 16
#3
In reply to #1

Re: Medieval Physics - Siege Engines

09/04/2014 10:28 AM

Good eye Andy!

Reply
Guru
Engineering Fields - Optical Engineering - Member Engineering Fields - Engineering Physics - Member Engineering Fields - Systems Engineering - Member

Join Date: Apr 2010
Location: Trantor
Posts: 5363
Good Answers: 646
#5
In reply to #1

Re: Medieval Physics - Siege Engines

09/04/2014 2:14 PM

Yep. Should have mirror-imaged the two sides.

(Twisting one side only could work with the proper design, but the 'fixed' picture above illustrates the principle better.)

__________________
Whiskey, women -- and astrophysics. Because sometimes a problem can't be solved with just whiskey and women.
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#6
In reply to #5

Re: Medieval Physics - Siege Engines

09/04/2014 3:54 PM

Perfect!!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Guru
Technical Fields - Project Managers & Project Engineers - New Member

Join Date: Jun 2014
Posts: 624
Good Answers: 33
#2

Re: Medieval Physics - Siege Engines

09/04/2014 7:09 AM

One of my favorites was always the Turtle, it has other names but the idea is to dig under the fortress walls and then fill the tunnel with sappy dunnage and light on fire, soon the tunnel collapses bringing the wall above it down with it.

The Turtle was a protective covering for the miners digging below the tunnel walls, it seems some citizens would like to drop things on them from above. Here is another good link about siege's:

http://www.historynet.com/medieval-warfare-how-to-capture-a-castle-with-siegecraft.htm

__________________
Hey Isaac, catch! ...oops, that's gonna leave a mark...
Reply
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7195
Good Answers: 416
#4
In reply to #2

Re: Medieval Physics - Siege Engines

09/04/2014 11:39 AM
Reply
Guru

Join Date: Aug 2009
Location: Glen Mills, PA.
Posts: 2385
Good Answers: 114
#8
In reply to #2

Re: Medieval Physics - Siege Engines

09/07/2014 9:24 AM

I don't know what "sappy dunnage" is but "sapping" is the act of trenching towards an enemy fortification. The Royal Engineers use "Sapper" instead of "Private" for its lowest rank.

__________________
In a time of universal deceit, telling the truth is a revolutionary act. George Orwell
Reply
Guru

Join Date: Feb 2008
Location: Large hole formally occupied by furry woodland creature.
Posts: 3385
Good Answers: 97
#7

Re: Medieval Physics - Siege Engines

09/05/2014 5:24 PM

This led to the development of the early carnival or amusement rides. The attire and demeanor of the operators has changed little over time.

__________________
CRTL-Z
Reply
Guru
United States - Member - Lifelong New Yorker Popular Science - Biology - Animal Science Technical Fields - Technical Writing - Technical Writer

Join Date: Mar 2008
Location: NY
Posts: 2409
Good Answers: 59
#9

Re: Medieval Physics - Siege Engines

09/09/2014 7:15 AM

And here for another old CR4 project: http://cr4.globalspec.com/blogentry/7248

Reply
Reply to Blog Entry 9 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Andy Germany (2); Brave Sir Robin (1); liznjerry (1); Massey (1); passingtongreen (1); SavvyExacta (1); Unredundant (1); Usbport (1)

Previous in Blog: Medieval Physics - Jousting   Next in Blog: Do We Finally Get Hoverboards in 2015?

Advertisement