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: The Skeleton of Mechatronics   Next in Blog: Medieval Physics - Jousting
Close
Close
Close
15 comments

Medieval Physics - Bows & Arrows

Posted August 12, 2014 7:00 AM by cheme_wordsmithy
Pathfinder Tags: olympics
User-tagged by 1 user

Of the many interesting events that take place in the summer, one of my favorites are Renaissance fairs. Seeing the participants in character and costume is an entertaining tribute to the days of knights and castles. However, the combat and jousting presentations rarely do justice to their crafts. As such, I thought it would be neat to dive into some of the science behind medieval sport and combat. To start, let's take a closer look at a practice that predates recorded history: archery.

Archers (users of the bow and arrow), were a common element among most warring nations in Medieval times. Before the age of gunpowder, bows were the only weapons available to foot soldiers that could significantly extend their range of combat. Some bows (specifically longbows) had the ability to launch a deadly arrow over great distances and with great force. Between the 14th and 16th centuries, the English longbowman (seen left) was a force to be reckoned with due to the range and power of his weapon.

While there is a lot of diversity among bows and arrows, all essentially consist of three parts:

1. the bow (or bowstave) - a flexible arc shaped piece with a handle grip near the center, a notch to hold the arrow, and attachments for the string at either end. They can be made from wood, bone, metal, plastic, or carbon composite

2. the arrow - a straight projectile made of similar materials to the bow, with a pointed metal blade on the front, and fletchings (plastic fins or feathers) on the back.

3. the bowstring - a strong thread of hide, intestine, or artificial materials attached to both ends of the bow to hold it taut.

A bow and arrow works like a spring. When the archer pulls the string back (called drawing), the string puts compression and tension forces on the bow, bending it and storing elastic potential energy. When the string is released, the tension between the bow and the bowstring causes the string to move forward rapidly as the elastically deformed bow returns to its original position. The result (hopefully) is a large transfer of energy from the string to the attached arrow, turning it into a high speed projectile.

When released, there is a certain amount of force put on the back end of the arrow from the bow and the archer's fingers (or other release mechanism). This force causes the arrow's backend to wobble. The fletchings on the arrow catch the wind in order to correct this movement and help the arrow fly true. Larger fletchings will correct wobble faster, but will create slightly more wind resistance. Configuration of the fletching into different patterns (helical or offset vs. straight) can add spin to the arrow to further help dampen oscillation.

There are a number of other variances in arrow construction that can be chosen based on the preferences and shooting style of the archer. The same goes for the construction of bow, which needs to be much more fit to the user than a firearm in order to shoot well. Bow length, draw length and draw weight are the three biggest factors by which bows will vary.

Bow length is obviously important because length determines the size, which must fit to the size of the shooter and his needs. Power increases with bow size, however, a recurve style bow will generate more arrow energy than a straight bow of the same size. This is because of the curves near the limbs, which allow for greater energy storage and more efficient energy transfer. Because of this, the recurve bow was preferred in situations (such as on horseback or in wooded terrain) where extra length could affect an archer's mobility.

A related characteristic is draw length - the distance the archer pulls back the string, measured from the nock point on the bow. Bow size and the size of the archer determines draw length, which in turn affects the size and length of the arrows used. A basic method for estimating appropriate draw length is to divide the archer's arm span by 2.5. Having too much or too little draw can affect accuracy and shooting consistency.

The draw weight, which is the max resistance of the bow when being pulled back, is also very important for the archer to consider. A higher draw weight means more strength is needed to pull and hold the bowstring in tension, but it also means a more powerful shot. Yeoldarcheryshop.com provides a nice chart that correlates draw weight (DW) to archer weight:

Small child (50-70 lbs) --> 10-15 lbs DW

Child (70-100 lbs) --> 15-25 lbs DW

Most women, boys from (100-130 lbs) --> 30-40 lbs DW

Women above average strength; youth boys (130-150 lbs) --> 40-50 lbs DW

Most men (150-180 lbs) --> 55-65 lbs DW

Muscular young men and larger men (>180 lbs) --> 60-70 lbs DW

Compare these numbers to back in Medieval times, when estimates say the draw weight of the longbowmen ranged anywhere from 80 to 180 pounds! Pretty unbelievable.

Today, archery and bowhunting has advanced to the use of the compound bow, utilizing pulleys and wheels to generate more power and accuracy with less exertion. Unlike recurve and longbows, which have a linear relationship of draw weight to draw length, compound bows have a parabolic relationship, because the levering system of these bows allows for a lower draw weight when extended past a certain draw length.

Despite such advances in technology, the art of the recurve bow has been preserved in the Olympics, keeping alive a fascinating skill and practice that has been around through the ages.

Sources:

The Mechanics of Arrow Flight

Bow Sizing and Adjustment Guide

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".
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 22569
Good Answers: 409
#1

Re: Medieval Physics - Bows & Arrows

08/12/2014 7:20 AM

It's interesting to see what our resident expert has to say about this.

One can analyse the mechanics of this. but Experience of actually cutting a down a yew or elm, drying it (or a better term conditioning it), and then actually making the bow.

With this experience, I would gather one becomes close and personable with each and every bow. Where each and every bow has it's own personality and know the reasons for it.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Reply
2
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16498
Good Answers: 661
#2

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:15 AM

A reasonable summary, with a few minor errors.
Medieval bowstrings were usually linen or hemp. Native American bowstrings usually sinew or rawhide.
The rough guide to draw length is fairly useless, as it depends mostly on shooting syle.
I usually draw about 28", but if I shoot a Warbow I go for a medieval style draw of 31-32".
There is no mention of the archers paradox which is probably a relief as most people don't understand it. The Wikipedia entry on it is good (well it is ever since I edited it)

The guide to draw weights is good. The heaviest I'd shot was 100#, the furthest was 302 yards.

Del

__________________
health warning: These posts may contain traces of nut.
Reply Good Answer (Score 2)
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16498
Good Answers: 661
#3
In reply to #2

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:36 AM

From a physics point of view, it's pretty amazing that a medieval longbow has a linear force draw relationship. If you treat a bow limb as a beam, all the physics books give an analysis for small deflections, but a bow limb has a large deflection. Another interesting thing is that the tip of the bow limb only moves about 8 or 9 " while the string draw back about 3 times that, thus it is giving a mechanical advantage/leverage/amplification of movement... call it what you will.

The arrow velocity vs energy relationship is also interesting too, maximum energy not being at maximum speed. A heavy projectile going slower can hit home harder than the lighter projectile. As an example my 302 yard shot was with a light flight arrow, whereas a full weight medieval arrow with a shaft as thick as your index finger a heavy steel head and fletchings 7" long would only go about 200 yards, the latter would penetrate plate armour but the flight arrow wouldn't, mind it would seriously annoy a horse or a lightly armoured foot soldier. The heavier arrow is also more efficient as it absorbs more of the energy of the bow. As a grossly simplified view if the bow limbs and the arrow weigh the same, then half the energy will go in the arrow and half will stay in the bow limbs, if the arrow is twice as heavy as the limbs it takes more of the energy. If you shoot with no arrow, all the energy stays in the bow and it may explode.
They say a bow is 7/8 broken at full draw... it's nearer 9/10

Del

__________________
health warning: These posts may contain traces of nut.
Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 22569
Good Answers: 409
#4
In reply to #3

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:46 AM

"A heavy projectile going slower can hit home harder than the lighter projectile."

Yes I'm quite familiar with that and know where you're coming from.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30802
Good Answers: 1722
#5
In reply to #2

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:49 AM

I'd hate to get in arrow fight....100lb pull, I mean how many times can you pull that before you get the shakes....I watch these medieval battles where the groups exchange arrow fire for days on end....It seems unrealistic....

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 22569
Good Answers: 409
#6
In reply to #5

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:55 AM

great question,... and what kind of people made up those archers, farmers, conscripts?

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16498
Good Answers: 661
#7
In reply to #5

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:55 AM

I don't shoot it any more, I trained up to do it, but I could shoot 70# no prob for extended periods.

At a recent shoot there was a timed target, as many arrows as you could shoot in 30 seconds, the target was a flag 120 yards away. The average was about 6 arrows, which was what I did, I watched the first land and then just drew and loosed repeatedly. I got 3 arrows within 6' of the flag. I was shooting a 70# bow.
The heaviest bow I've made is a 130# Yew warbow for a friend of mine who is substantially younger than me.

Every man and boy had to own a bow and arrows and practice every Sunday by law.

If you get on you tube and look for "Tudor Monastery Farm Christmas Special" 40 minutes in is some footage of me and a few friends shooting with the presenters...

Del

(PS We try to avoid the term "fired" that didn't come in until the introdution of firearms

__________________
health warning: These posts may contain traces of nut.
Reply
Guru
Popular Science - Evolution - New Member Popular Science - Weaponology - New Member

Join Date: May 2006
Location: The 'Space Coast', USA
Posts: 11112
Good Answers: 918
#8
In reply to #5

Re: Medieval Physics - Bows & Arrows

08/12/2014 8:59 AM

"I watch these medieval battles where the groups exchange arrow fire for days on end..."

Probably because neither side hits anything. :-)

Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 22569
Good Answers: 409
#9
In reply to #8

Re: Medieval Physics - Bows & Arrows

08/12/2014 9:08 AM

Hate to be the guy that has to run out there and pick up all the arrows because they were running out.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Reply Off Topic (Score 5)
Guru

Join Date: Apr 2014
Posts: 1869
Good Answers: 67
#11
In reply to #9

Re: Medieval Physics - Bows & Arrows

08/12/2014 12:39 PM

Nah, they just shot the other side's arrows back to them; "Here, mates, try again!"

Reply Off Topic (Score 5)
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 22569
Good Answers: 409
#12
In reply to #11

Re: Medieval Physics - Bows & Arrows

08/12/2014 1:05 PM

Well I was kinda had in mind like on a golfing range, the guy that drives the sweeper that picks up the balls. You can really hear the balls bouncing off his cage as he drives through.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Reply Off Topic (Score 5)
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16498
Good Answers: 661
#13
In reply to #11

Re: Medieval Physics - Bows & Arrows

08/12/2014 2:44 PM

That's not far from the truth!
There was a famous battle Towton in the English War of the Roses which took place in a snow storm with a howling wind (I'd have asked for a postponement myself or asked to be excused, saying I had a note from my Mum....) One side would watch the opposition arrows drop short due to the headwind, they would then advance, pick up the arrows and shoot them back, the tailwind now sending them into the enemy ranks.

(If you scroll down the wiki entry to the section headed 'Fighting' it describes it)

The thought of a medieval battle in a snow storm is pretty horiffic.

Del

__________________
health warning: These posts may contain traces of nut.
Reply Off Topic (Score 4)
Guru

Join Date: Apr 2014
Posts: 1869
Good Answers: 67
#14
In reply to #13

Re: Medieval Physics - Bows & Arrows

08/12/2014 6:40 PM

Fascinating! Thank you.

Reply Off Topic (Score 5)
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30802
Good Answers: 1722
#10
In reply to #8

Re: Medieval Physics - Bows & Arrows

08/12/2014 9:15 AM

...or maybe there was just a lot of them....

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru

Join Date: Dec 2007
Location: Mumbai, India
Posts: 1985
Good Answers: 25
#15
In reply to #2

Re: Medieval Physics - Bows & Arrows

08/13/2014 6:52 AM

Ya this your subject and you are master in this technology..

__________________
"Engineers should not look for jobs but should create jobs for others" by Dr.Radhakrishnan Ex President of India during my college graduation day
Reply
Reply to Blog Entry 15 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:

Anonymous Hero (1); Del the cat (4); europium mkII (2); phoenix911 (5); SolarEagle (2); suresh sharma (1)

Previous in Blog: The Skeleton of Mechatronics   Next in Blog: Medieval Physics - Jousting

Advertisement