# Physics of a Zero- G

Monday, January 19, 2004 1:38 PM
I'm sure this has been discussed before, but I could not find a topic about this. How does the inversion create weightlessness? I know it is something about the heartline, but I don't really understand how it creates zero g's. Are there any illustrations that show how they work? I'm asking this question for a physics class. Thank you.
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Monday, January 19, 2004 2:13 PM
If I'm not mistaken, a zero-G roll works in much the same fashion as a regular parabolic hill. Since you're inverted at the apex of the roll, you are still planted firmly in your seat (as opposed to a regular hill). But as you begin to come out of the roll and the train starts to dive, you feel the zero-G effect. The effect is exaggerated because you are rolling along one axis and diving along another (roll and pitch).

But that's just my take... I only made it through 5 semesters of engineering.

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Monday, January 19, 2004 2:27 PM
Since I made it through 11 semesters of engineering, I'll take my stab at it:

The centrifugal force (which isn't a real force, but we won't go into that) throws you to the "outside" of the roll while you're executing it - same theory as Music Express rides and Rotors that throw you to the outside of a spinning axis. So, when you're in the apex of the roll, theoretically, the centripital/fugal force throwing you "out" of the roll is strong enough that it counteracts gravity and you seem to "float" in the air, rather than be glued to your seat. The floating in the post-apex part of hte roll that olsor is talking about is just teh centripital/fugal letting go and gravity taking back its hold which is weird enough that it feels like you're still floating.

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Monday, January 19, 2004 3:39 PM
So the weightlessness is felt at the apex of the hill, and you still feel the floating sensation on the pull out of the twist?
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Monday, January 19, 2004 4:49 PM
That's probably right. Although I'm wondering if your upward inertia is enough to counteract or overpower the outward push of the roll as you approach the apex. In my experience, I tend to feel weightless just after the apex as you start to travel downward.

But there's also a difference in sensation depending on where you sit in a roll. Correct me if I'm wrong, but if you traverse a left-hand roll, as in this picture, the people sitting on the right-hand side of the train will feel more outward force entering the roll (since their turn radius is wider than the left's), and the people sitting on the left-hand side of the train will feel more outward force exiting the roll.

I might not have gotten that exactly right, but I noticed a huge difference in Alpengeist's zero-G roll when I sat on the left, then the right. On the right side, the roll felt like it would toss me, and on the left side I merely felt like I was rolling over. *** Edited 1/19/2004 9:54:08 PM UTC by Olsor***

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Monday, January 19, 2004 6:06 PM
Yes, it is different by seat. Remember, that roll is designed based on the middle of the train. The people on the inside of the roll will have too quick of a direction change to feel anything more than like rolling off a couch, but the people on the outside have a relatively more gradual change in direction, so they have a microsecond longer to experience the changing of the direction of the forces on their body - but luckily for us coaster junkies, our bodies are sensitive enough to catch that change and make it into adrenaline ;)
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Monday, January 19, 2004 6:46 PM
That's why I always choose the left hand outside seat on PGA's Top Gun and SFMW's Medusa. For no other reason than to be flug around like a rag doll through the zero-g rolls, both rides produce incredible laterals through this roll.
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Monday, January 19, 2004 6:55 PM
The path that the trains follow in a zero-g roll are designed to be close to what they'd do if they were just launched off the track and entered freefall, minus the twist obviously. This should produce a 0 g effect because it's simulating the path of a freefalling object, and the twist is just thrown in to make it cooler and it theoretically shouldn't affect the vertical g's because the track follows the "heartline" of the riders.
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Monday, January 19, 2004 11:30 PM
As discussed in a previous topic, (as confirmed by Keith aka Badnitrus) the axis of rotation is actually way below the heartline of the riders. Somewhere around the feet. Thus, the centripital force in the roll is actually towards your head.

I don't understand how people on the outside seats of the train have a slower direction change. The rows move as a whole. If anything, the outside seats travel further (being further from the axis of rotation) and therefore move faster.

My understanding of the zero-g roll is that, in the middle rows of the train, you're tracing the parabolic arc, creating a zero-g effect. The twist heightens the sensation because you're upside down when you're weightless.

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Tuesday, January 20, 2004 9:25 AM
Andy -
Think of it like a tube with a thick wall (the wall being the seats. The inside circumference (sp?) is a lot smaller than the outer one, but they have to make the same distance during the twist. Regardless of where the "heartline" is, be at the rider's heart or feet, something is controlling how fast that thing turns. Now, the inner part of the tube doesn't have to "travel" as far to make it in the required time, but the outer part does. It's the same concept of speedskating that the person on the inside of the turn will usually come out in front in a dead heat.
Now, since the outside is "traversing" a longer distance, there's more "time" to feel the forces, hence the more floating feeling, rather than the quicker "time" of the inside which feels more whippy.
Make any sense? You can do it in a car too - wait til late at night when there's no one else coming, and take a relatively tight left hand turn in your lane, then try it by swinging out into the other lane before coming back to yours at the end of the turn - same effect.
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Tuesday, January 20, 2004 12:30 PM
/adjusts oxygene level in room, puts on gloves, dims the lights, takes Stengel bible carefully out of its vacuum globe and opens the book with trembling fingers. Moves lips while silently reading page 120 to himself/

Well, the zero-g roll or "revolution" as it is called by its creators is actually a 0,1 g roll. Unlike on the top of an airtime hill, there is always a slight pressure which "guides" the body through the inversion.
The forces go down to 0,9g on the incline, reach 0,1 on the apex and go up to 0,9 on the decline.
Nevertheless this is an remarkable feature, since the body is close to weighing nothing, while the lateral acceleration is just 0,6 g throughout the revolution.

The "heartline spin", found on the Intamin loopers, was initially designed to simulate a flipping car in an accident (go figure). The rider has to endure -1g and is practically falling out of his seat while inverted.

/solemnly closes the book with clouded stare, replaces book into vacuum globe, reciting obscure mantras while switching numerous levers with dreamlike sincerity, disposes gloves and puts oxygene level back to normal. Closes heavy door and goes upstairs where mother is preparing liver for dinner./

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Tuesday, January 20, 2004 6:54 PM
Brett- Maybe I don't understand your point, but I don't see how the outside seats could ever have a slower direction change.

The row is all one fixed object. The angular acceleration around the axis of rotation (dw/dt) of the row is the same for all seats. Thus, the direction change is the same for all seats. However, since the inner seats have less distance to travel in the same amount of time, less linear force is applied in acceleration and deceleration (dx/dt).

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Tuesday, January 20, 2004 8:46 PM
ApolloAndy said:

Brett- Maybe I don't understand your point, but I don't see how the outside seats could ever have a slower direction change.

My thoughts exactly, AA. Impulsive, I don't buy it. Could you explain differently? I also only had about 5 semesters of Engr. (honestly not trying to be sarcastic), I'm not trying to be an expert, but if you're right on this I would like to understand why.

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Wednesday, January 21, 2004 10:51 AM
*smacks head* My bad dudes! The whole thing revolves around me seeing inside and thinking outside and blah blah blah ...

Ok, let's try this again (and I think we're all saying the same thing here).

The seats closest to the track spine in the roll have less distance to travel to accomplish the same roll around the "centerline" of the car than the seats furthest from the track spine. Correct? Ok, what I'm seeing in my head are two arrows pointing in the direction of the active force on the people in the train. The one coming out of the folks nearest the spine will really whip around the spine, faster than the one at the centerline of the train. Conversely, the arrow on the outside will move "slower" around the twist than the arrow at the centerline.

Make any more sense? I believe that its this difference in "speed" due to distance from the center of rotation that causes the different sensations depending on your seat in a zero-g roll.

btw tricktrack - nice one with the "holy writ of werner" ;)

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Thursday, January 22, 2004 12:45 AM
It doesn't make any more sense. The arrows aren't the same length because the train moves as a unit. The outside arrow is longer than the inside arrow.
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Thursday, January 22, 2004 12:50 AM
Huh? Length?

Ok one last try then I give up. You and I are on a football field. Someone draws a B&M zero-G looking straight down the spine (so basically all you see is a box with a circle going around it representing the "rails"). Now, add in a circle for the approximate location of the center of the train as it executes that roll. Finally, add a circle for the outside seat, and one for the inside seat. Now, you and I run at the EXACT same speed, but I run around the outside "seat circle" and you run around the inside one. You're going to get back to your original starting point before I do. I have a longer distance to travel to get to the same point. Therefore, I have to move faster.

Get it? (If not, this is going nowhere and I give up ... my girlfriend's the teacher, not me ;) )

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Thursday, January 22, 2004 3:04 AM
Brett- I get what you're saying but wouldn't that mean that the inside seat is more floaty than the outside? Since the outside is moving faster you'd get more of that "whip effect."

Here's an analogy. Look at a record player (remember those?) from above. Pretend its the zero-G roll looking dead on as Brett mentions above. Put a coin halfway across the turntable and one at the edge. Start the player. None gain or lose position in this little "race" but the outer coin is obviously covering more ground because the circumference is bigger there than the coin at the halfway. Now look at those 2 coins as the inside seats, and outside seats respectively; and the pin that would hold the record as the heartline as the train travels through a zero G. In relation to the inside seats, the outside seats cover more area than the inside seats in the same amount of time.

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Thursday, January 22, 2004 3:13 AM
At first I thought you where going to say something like: Image a footballfield and someone draws a B&M zero ge-roll on it- now, visualise two square boxes, one at the center of the football field, the other at a height of about 10 meters above ground. Now, the one 10 meters above ground revolves slowly around and around, and then - the sun suddenly starts to break through the clouds - and you realise that you are in a deep forest. Like some fries with that?

No - seriously I think you're probably right with your explanation:
In the direction of the train travelling, all seats have the same speed. But concerning the path travelled resulting from the rotation of the roll, the outside seat travels more distance.
Just like the length of a groove traveled by the stylus when playing back a record travels less and less length per revolution the deeper into the record.

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Thursday, January 22, 2004 9:32 AM
Sorry, I'm 21 - record players are ancient relics ;)

I'm not sure where you're going with the deep forest and the fries, but hey, sign me up ... but yea, I think yinz gots the idea I was tryin to get across - but I think who gets whipped and who gets float is more a matter of opinion (either that or I'm burnt out thinking about this). Either you feel that more distance or more speed gives you the whip.

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Thursday, January 22, 2004 1:20 PM
But the outside seat covers more distance and has greater speed. (And whip isn't a matter of opinion. It's a matter of physics. (i.e. jerk i.e. dddx/dtdtdt))
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