View Full Version : the physics of falling

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10-23-2005, 08:54 AM
ok i hope someone can help me with this... i have to do a science fair project soon ( :yuck: ) and one of my ideas was to show why we dont get hurt when we fall in aikido, like why does our hand slapping the mat take away the pain of the impact on our bodies, and my teacher approved the idea and said it would be a great project, but i cant seem to find any resources or information on it from an actual scientific point of veiw, so does anyone know of any place i could get info? or even if there is a physics term for break falls?

Dirk Hanss
10-23-2005, 03:15 PM
Hi Mal,
I do not know very much about it so just a few ideas.
Pure physics aspects:
Slapping the the mat takes some momentum out of the falling body and turns direction so that you might roll a little biit instead of just crash straight. I guess these effects are important, but you should not overweight them. It is just a light arm you are using here.
Slapping the mat activates the muscles in your shoulder and thus they can better protect the bones. I think this part is really important, as I had some hard breakfalls in the street, where I could not use my hands or arms, but was well off afterwards just by activating and hardening my muscles.
Psycologic effects:
You think you are doing somthing, even that helps.
You prepare for known pain (by slapping). In addition to some biochemical effects the additional pain from the breakfall feels much less than if you are not prepared.
Slapping helps you to find out, when you really hit the soil. So you are much better prepared for the split second you need to tense your muscles. This comes back again to bio physics or chemistry or "learning body".

Just a few thoughts, but I do not have literature for you.

Kind regards Dirk

Lorien Lowe
10-23-2005, 05:41 PM
Look in any general (college) physics text for things like force, acceleration, and pressure.


Janet Rosen
10-23-2005, 07:13 PM
Doctor Wendy Gunther did a wonderful essay on just this topic; I thought it was on aikiweb but cannot find it now. I'll start searching....

Berney Fulcher
10-23-2005, 08:24 PM

The basic idea behind slapping is just to increase the area and time as you hit, but she really does do a nice job of explaining it.

I'd love some further explanation though... We tried to work out what the units should be in her equations and could never make it come out in correct units of energy.

10-23-2005, 08:41 PM
oh man... i love physics and math but i absolutely hate doing calculations with units... i always just leave them out and then write my answers with the correct unit on it in the end. (i know thats a bad job, but at this point in my life its easier)

wow, thank you so much for that article... it was really helpful!!!!

10-26-2005, 04:03 PM
I think one aspect not mentioned in the physics of falling so far is the changing vector relationship and the force over time relationship.

In addition to expanding the surface area absorbing the impact of the fall we also change the vectors of the forces involved:

A rolling breakfall, for example, takes the velocity of the throw and changes the vector from "down", where the nasty ground is waiting to hit us, and changes it to "forwards" or "backwards". This significantly diminishes the vertical component of the force vector, lessening the impact.

Even sidewards breakfalls work along similar lines.

Another really interesting physical aspect involved in breakfalls is the use of inertia/centripetal forces (sorry, I refuse to call them centrifugal forces).

Try every bored office workers favourite physics experiment: Sit in a rotating chair (your computer chair will do the trick too), extend your arms, spin the chair and pull your arms inward. (Or better yet, get someone else to spin you around instead.) The effect is the same as seen in icescating: As you pull your arms inward you accellerate.
A rolling breakfall works with the same principle to achieve the opposite effect: As we roll, we gradually increase the radius formed by our body. This not only increases the surface area in contact with the ground (reducing the amount of force applied to the parts of the body in contact with the ground) but also slows our rotational velocity.

You could also mention the breathing aspects involved...

10-27-2005, 02:29 AM
I think one aspect not mentioned in the physics of falling so far is the changing vector relationship and the force over time relationship.

In addition to expanding the surface area absorbing the impact of the fall we also change the vectors of the forces involved:...

Did you hear that swooshing noise? It came from this post going right over my head :)

Ben, you are such a clever guy (and I am not being sarcastic here) - we watched Monday night´s video (thanks for filming by the way) and your commentary is not only funny but also very clever. I am really impressed.

10-27-2005, 02:47 PM
A rolling breakfall, for example, takes the velocity of the throw and changes the vector from "down", where the nasty ground is waiting to hit us, and changes it to "forwards" or "backwards". This significantly diminishes the vertical component of the force vector, lessening the impact.

You can't change the vector force. You can only convert the force/energy into other form of energy. The idea of changing "down" force into "forwards" force defies basic physics.

I don't think Wendy's explaination good either.

Now let's do a experiment. Try to do 2 jumps from a high place into a hard surface, say 2' high.

1. In the first jump, try to plant your feet solidly into the ground.

2. In the second jump, try to do a few hopps after your feet touch the ground.

I'm sure you'll find the first jump hurt a bit while the second is fine. If you find no difference, try to jump from 5' high.

In your hop jump, you actually bend your kneels and body to convert(store) the "down" energy.

In the aikido breakfall, you bend your body (using abdominal muscle) to convert(store) the "down" energy. In the right breakfall, you should feel your lower body going up (relatively). The land slapping is here to facilitate the timing, and assist the function of weak abdominal muscles. That's why lots of time, you don't hear and see the hand slapping in the breakfall.

I guess the original poster can do a survey of the jumpin experiment, say ask 10 people jump for him to record the reaction, and fill a form in terms of pain scale from 1 to 10.

He can also construct 3 objects of hard paper.

1. a long single unit with one end heavier.

2. two units (one heavier) connected together by a elastic string.

3. the same as 2, but has a simple mechnism in the heavier unit that once hit the ground, it props up the other unit.

Then free fall them from the same height again and again. After a few, you shoul find 1 has the most damage while 3 (which is simulates a breakfall body) has the least.

Being nage may depends on your Ki, but being uke, a light guy with 6 packs abdominal muscle wil take breakfall better than a heavy guy with 6 pack beer belly.

My advice to heavy guys, reduce your waistline or slap hard. It does help.

11-09-2005, 04:08 PM
As a physicists, this thread was tempting to read, but dangerous in which to get involved. This is a very complex system. I doubt that there has been a lot of good science focused on it. Try sports medicine and perhaps military research for studies on this. As a physicist, I like spheres (cylinders and cubes if I'm feeling adventurous). I might be able to tell you what is happening to objects this simple without computer simulations.

What can I tell you about what I THINK is going on in a roll or break fall?
I will agree with the previous post that reducing/minimizing the "yank" to any particular part of the body seems to be the most important aspect of successful fall ukemi. The yank in physics is defined as the time derivative if the force. Since this is a change in force over a change in time, the two most obvious ways to make it smaller are to have smaller forces and to have those forces act over larger time. The force to any particular location can be reduced by applying the pressure to a larger area or just making contact at any particular time with less pressure (force per area). Now momentum can be changed, but must be conserved. The integral of force (itself a time derivative of momentum) is called the impulse or change in momentum. The total change in momentum is constant in two different ways of stopping, but notice that the product of the force and time can be the same if for instance the force is halved and the time doubled.
Slapping and sliding can also convert kinetic energy into noise or heat.
So, that is what I guess is going on, but is just conjecture without testing.

If you want an experiment (and it isn't science without one), here is my suggestion.
Eggs (several dozen will be needed)
paper and/or foam plates and cups
glue or adhesive tape
Get eggs, hard boil them (messy otherwise), they will be the object that you drop. How do you gauge the damage of the fall? Two ways: after each drop measure the total integrated length of all the cracks and the total cracked area of the shell (this will be difficult, but hopefully you will be able to show a correlation). I would suggest a third way, massing the chips of the shell that are totally separated from the whole, but removing them will destroy your other data.
Alright, now you have a measurement in unknown units. That is fine. With good results and more funding your future students can refine that.
Trials, of dropping eggs, with different "body" configurations to protect them.
I would attach "limbs" to the cups, cut from the plates. Put the egg in the different cup configurations and drop from different heights (slowly increase until visible breakage, you can even note the height of first breakage, this is probably much better than measuring the cracks alone). Particularly look at making "j" shaped setups. Keep the total amount of paper or foam relatively constant. For example, egg in foam cup, with half a paper plate (cut) on each side (two legs) vs egg in foam cup with quarters of a paper plate, two to a side (two legs, twice as thick each, but half as long).
Keep the egg in the cup without reinforcing it, say two strips of tape crossing the opening. Try to seat each egg with the same force. The nice thing about this setup is that you should be able to drop the same protection device with different eggs in it. Model the devices after good and bad fall techniques. Drop the same device with different orientations to the ground. Hopefully, you get the idea. This should be fun. Tell me how it goes. If you have questions, you know where I am.