The Physics of Segway... (posts copied from another thread)

[Segwaiian]

The author has some flaws in his thinking. While this may be true at very low speeds ( greater than 0 and less than maybe 2 mph ), I think you'll find the Segway -rapidly- becomes more forceful as the speed increases. This is just how f=ma works. Every time you double the speed, you quadruple the force of impact. No amount of "push back" from the handlebars is going to overcome that force at a certain point and that same "push back" does, for all practical purposes, nothing to slow the body mass of the rider. The force of impact -has- to go somewhere.


Shoot, here i go hijacking a thread, again. And, this time it's one that I started! :rolleyes:

So let's get this over with before the engineers and physicists get involved.

An object moving at a constant speed (not accelerating) has a net force of zero. (f=ma => m X 0= 0) It would take a certain amount of force to get that mass to a higher speed, but that depends of the acceleration rate.

p= mv (Momentum= mass X velocity)

Double the speed of a Segway and it has twice the momentum. We definitely have more momentum than the average pedestrian. The results of the meeting of said objects also depends on the vectors involved.

And that's about the extent of my physics background, thank you. :)

Having written all that, the bottom line is that if we come into contact with most pedestrians, it's the person on foot that loses.

My only actual fall, to date, was in order to avoid hitting a pedestrian. I was following behind her, at her walking speed, waiting for a wider spot up ahead to pass her. She veered to the right to look at a newspaper dispenser, so I figured I could pass her on the left without doing my usual "On your left" warning. She suddenly changed her mind and actually veered back to the left even farther. There was no way to slow down in time, so I turned sharply to the left, dropped about 3-4" off the sidewalk onto wet ferns, lost traction, and then was glad I was wearing my helmet. :D

The woman was very nice and asked me if I was OK. I assured her that I was fine and didn't mention her role in my acrobatics. I wonder if, since I didn't implicate her, she thought I was a reckless glider?

Aloha,
Roger

[DarthSegVator]

[QUOTE=quade;169337]No amount of "push back" from the handlebars is going to overcome that force at a certain point and that same "push back" does, for all practical purposes, nothing to slow the body mass of the rider. The force of impact -has- to go somewhere.QUOTE]

I disagree.

A glider/Segway will abruptly cease forward motion when an encounter occurs as suggested. The momentum is not only halted, the motors reverse to compensate. If the glider continues to be propelled forward, they have not been operating the device in the proper fashion.

Let's say you have a mass of X (200 lbs. person) contacting a person Y (200 lbs. person on Segway for a total of 300 lbs.).

The 300 lbs. mass (Y) not only stops upon contact with the 200 lbs. mass (X), but reverses direction to prevent the mass (Y) from continuing its' forward motion (at least the Segway portion of the equation). The person can leave the Segway and continue forward, but the Segway will not. Again, if the person is operating the machine properly, they will stop too.

A human mass simply tries to stop....a Segway stops.

[KSagal]

I am sure someone will try to take me to the woodshed on this thought, but...

Much of my mass, as a man, is high in my body, in my torso and chest...

So, the center of mass, when on my feet is high.

When I am on my segway, I do weigh 1/3 more, and therefore have more mass, but there is a significant mass below my feet, very low...

So, the center of mass, when on my segway is much lower...

The function of friction applied to the sidewalk is a major force in stopping the momentum of my movement. This could be the friction of my feet not moving as fast as my chest while I try to stop running, or the friction of my tires not moving as fast as my center of mass when trying to stop gliding...

It seems to me, that the closer to the point of stopping (the friction) that the center of mass is, the better...

Clearly, there is much more involved. I know this...

But, additionally to all else, the slowing segway platform tilts back...

The affect of this, is that the movement of mass, the momentum, is somewhat transferred to the base, as it is tilted lower in the back, higher in the front...

If there were force sensors, I believe it would record more pressure on the soles of your feet during a hard segway stop.

So... The friction of the tires on the sidewalk being good enough that they do not slip, the weight of the rider being somewhat shifted downward toward the platform, and the center of mass being lower to start with, lead me to conclude that the increased efficiency of the segway stop much more than compensates for the increased mass.

In other words, I believe the segway can stop faster than the same speed runner...

And I believe that this is a significant improvement on being hit by a segway compared to being hit by a runner...

A notable exception is that portions of the segway are very hard, and getting in the shins is not fun by a sneaker, and less fun by a segway...

[quade]

In other words, I believe the segway can stop faster than the same speed runner...

This, I believe is true.

However, we're not talking about stopping distances; we're are talking about impact.

During an impact at 12 mph, I'm not convinced that your feet would even remain in contact with the base. The collapsing body, the bending of the knees and the forward momentum of the legs and feet would, in my estimation make that unlikely.

If anyone actually cares to do my test, I think they'll be surprised at the force of a collision at 12 mph . . . or even 4.

[KSagal]

Much as I do not really want to agree with Quade, it does really matter what you impact with...

Several years ago, while gliding along at 10 or 12 miles per hour, on a clear cold day in town, on a sidewalk where I was utterly alone...

There was plenty of snow on the ground, but the sidewalks were clear, and the snow was several days old, so the sun had dried the sidewalks even though it was below freezing temperatures...

I came thru a slight turn and could easily see far ahead, but the 2 foot snow banks obscured my view of the sidewalk itself at the far side of the curve...

The wind had blown a soft drift of snow, about 5 or 6 inches deep, about 1 or 2 feet wide, across the sidewalk...

This impact was soft, on a scale comparing it to hitting a person or wall, but the seg slowed down very fast, and I went over the handlebars, and then the seg popped back onto it's wheels (I did not really completely lay down forward, just enough to buck me off) and it tried to climb thru the snow, and did because I was gone... It bounded off and hit some more snow and did an interesting series of maneuvers...


In this case, the seg did most definitely slow down without me... One of my true and few cases where I left the machine not of my own wishes...

[Segwaiian]

I was, of course, talking about the force of a collision, which I think you'll agree does in fact increase at a rate of the square of the velocity.

Sorry, I haven't taken physics since my sophomore year in college, which was so long ago that introductory computer classes basically taught BASIC. ;)

I'm having trouble with this square of the velocity thing. Even the f=ma equation wouldn't increase force by a squared increment. If you recall the formula, I could learn something form it. Any physics I talk here is a bluff. :o

I do recall that light intensity (or luminosity, or whatever) decreases by the square of the distance as you get farther away from the light source. But, please LET'S NOT USE THIS LAST (MIS?)STATEMENT TO TAKE THIS THREAD ANY FARTHER OFF COURSE. :D

Aloha, and Peace Out,
Roger

[Segwaiian]

It seems to me, that the closer to the point of stopping (the friction) that the center of mass is, the better...

But, additionally to all else, the slowing segway platform tilts back...

The affect of this, is that the movement of mass, the momentum, is somewhat transferred to the base, as it is tilted lower in the back, higher in the front...

So... The friction of the tires on the sidewalk being good enough that they do not slip, the weight of the rider being somewhat shifted downward toward the platform, and the center of mass being lower to start with, lead me to conclude that the increased efficiency of the segway stop much more than compensates for the increased mass.
...

Karl, two points:
1. I edited your post just to keep mine shorter.
2. I'm not picking on you, you're just the last person to go off on this physics thing (OK, I admit that I responded to Quade, which technically makes me the last one. But, mine was really short. :D )

So, guys, it's an interesting discussion, but there is a serious issue at stake in this thread. Can you guys somehow move Segway Physics 101 to a new thread, please? :)

And, when you do, I'd like to make a suggestion that we send this over to Mythbusters. I'm sure Adam would love this topic and they'll turn Buster into a pseudopedestrian. :eek:

Mahalo,
Roger

[quade]

If you recall the formula, I could learn something form it.

Okies . . . the actual formula specific to the task at had has to do with kinetic energy. (I have a tendency to use the shortcut of f=ma to massively represent just about everything involving power and motion {Newtonian physics}, but it's technically not the one we're really talking about.)

Kinetic energy is the amount of energy of a moving object has due to its motion and mass. During a collision, this energy has to "go" somewhere. It does not magically disappear.

Ek=1/2(mv^2)

Ek = joules
m = mass in kilograms
v = velocity in meters per second

All of the above said, you could just as easily have, m = pounds, v = miles per hours and Ek = a mythical unit I call "ouchies".

1/2(300x6^2) = 5400
1/2(300x12^2) = 21600

21600 ouchies is 4 times as great as 5400 ouchies. :)

Because of this quadrupling of energy every time you double the velocity, really bad things can happen if you get small objects going fast enough. For instance, a small pebble sized asteroid traveling at orbital velocities can have the same kinetic energy of say . . . a large truck at freeway speeds.

Wikipedia ref (http://en.wikipedia.org/wiki/Kinetic_energy#Calculations)

[Sal]

The original thread:

http://forums.segwaychat.com/showthread.php?t=18578

-Sal

[Segwaiian]

I moved this over, also.

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Quote:
Originally Posted by quade
Okies . . . the actual formula specific to the task at had has to do with kinetic energy. (I have a tendency to use the shortcut of f=ma to massively represent just about everything involving power and motion {Newtonian physics}, but it's technically not the one we're really talking about.)

Kinetic energy is the amount of energy of a moving object has due to its motion and mass.

Ek=1/2(mv^2)

Ek = joules
m = mass in kilograms
v = velocity in meters per second

All of the above said, you could just as easily have, m = pounds, v = miles per hours and Ek = a mythical unit I call "ouchies".

1/2(300x6^2) = 5400
1/2(300x12^2) = 21600

21600 ouchies is 4 times as great as 5400 ouchies.

Wikipedia ref

No, I don't remember, but I know it wasn't you, Quade.

OK, I get it. When I sacrificed Sig. Dispositivo and myself for the pedestrian, I experienced a couple of Eks.

Aloha,Roger

[Segwaiian]

Hey, you guys are still welcome on "...Circle the Wagons!!!", by the way.

My two cents, again: This would be great for a Mythbusters episode.

Aloha,
Roger

[quade]

And Who Said Not To Trust Wikipedia?

Wikipedia is a mixed bag.

For subjective topics they can be highly suspect.
For objective things like formulas, they're, generally speaking, a perfectly fine source.

[Segwaiian]

Hey, now I can post the lithium battery decay tables here and turn this into a battery thread! ;)

Sorry, this is a serious (Possibly boring to non-gliders) subject that lends itself to lighter moments. :o

I do think that this discussion could prove useful in situations where a community of Segway enthusiasts has to respond to an anxious and uninformed public. If there's a way to translate this theoretical discussion into validated results, it would be a valuable addition to our portfolio of knowledge.

Have at it, folks!

Aloha,
Roger

[quade]

If there's a way to translate this theoretical discussion into validated results, it would be a valuable addition to our portfolio of knowledge.

I believe you're right. That said, I think most Segway advocates would be disheartened to know the reality of Segway collisions as opposed to the mythology of the "handle bar push back" theory.