Save the date: Dollywood, Saturday, May 19, 2012

I am looking forward to this event. I have never been to Dollywood but I have always wanted to go. Wild Eagle sounds like a fun ride. I can't wait!

birdhombre said:
Gardaland's Raptor has a height requirement of 140 cm, which works out to about 55 inches. However, there's an *age* maximum of 99 years. :)

They also warn you that the ride has "poorly lit areas and a high possibility to create panic, fear, vertigo and/or claustrophobic reactions." O RLY?

Pretty lax when you compare it to Alton and Thorpe's everyone is strongly encouraged not to ride this policy and the skull and crossbones that adorn everything.

Both times Mystery Mine valleyed, maintenance was in control of the ride and the lift was running at half speed or slower. I would think the design would accommodate the vehicles making it just on ride vehicle velocity/momentum (I suck at physics), so the chain speed should be a non-factor, but I could very well be wrong.

Many discussions have gone on here about that and it basically comes down to the fact that the lift speed is a negligible factor in the overall speed at the bottom of the hill.

Which is very odd because the ride tested perfectly at full lift speed before the season started. Of course, these are the post-lift dips where the valleys occurred, so I don't know. Paging RideMan... ;)

This discussion is getting me think about the story I read about the Tidal Wave at SFGreat America hitting the bumper on the spike, and the hood of the front car flew off and hit a garbage can. Someone said it wasn't possible, but I was thinking - if the cable snapped behind the train, perhaps the energy released gave it the extra speed. There was also a story about how it happened on White Lightnin' at Carowinds, and people drove by to see a train stuck at the top of the spike, front car partially off.

It's just basic physics, guys, as we've been over many times. Horizontal motion (the car coming off of the lift) has negligible impact on vertical downward motion, as gravity pulls all things to the ground at the same rate. Checkout the Mythbusters episode where they fired a gun and simultaneously dropped a bullet. Both hit the ground at the same time.

I was pretty surprised to see Mystery Mine valleyed later in the day on Saturday. It actually opened up in the morning, and was running pretty well. A little jerky, but we got two rides on it in a row.

It's just basic physics, guys, as we've been over many times. Horizontal motion (the car coming off of the lift) has negligible impact on vertical downward motion, as gravity pulls all things to the ground at the same rate. Checkout the Mythbusters episode where they fired a gun and simultaneously dropped a bullet. Both hit the ground at the same time.

But, in that example, the two bullets traveled (very) different paths. In the coaster example, the two hypothetical trains are constrained to the same path by the track. Because the path is constrained, the additional kinetic energy at the top does translate into modest additional kinetic energy at the bottom. However, the delta between "full speed lift chain" and "half speed lift chain" is in the noise vs. the potential energy of a train at the top of the hill, all of which ends up as kinetic energy at the bottom, minus friction via wheels/wind/etc.

And, yes, the train should be able to complete the circuit from a dead stop at the end of any block, and that includes the lift hill.

I always thought that the faster a train was launched off the top of a hill, the faster it would be traveling at the bottom of the hill. Guess I need to watch more Mythbusters.

It does, but as the hill gets higher the affect of the chain speed diminishes. As a stupid example, if the drop is only 10 feet then there will be a significant difference in speed at the bottom of the hill if the chain speed is 5 mph versus 25 mph.

Brian Noble said:
In the coaster example, the two hypothetical trains are constrained to the same path by the track. Because the path is constrained, the additional kinetic energy at the top does translate into modest additional kinetic energy at the bottom.

But that was the point of the bullet experiment... the path doesn't matter. The bullet is "constrained" by its horizontal motion (caused by the explosion behind it), but it's still pulled to earth at the same speed by gravity.

Not the same experiment. That shows that horizontal speed/motion does not impact the acceleration due to gravity.

Fire a bullet straight down to the ground and drop a bullet straight down. Which is travelling faster when it hits the ground?

The only way to make the bullets land at different times is to fire the gun non-horizontally so that it has *some* vertical momentum (with lift-chain speeds, we're talking almost entirely horizontal momentum). g is constant at any given point on the planet's surface...so the Leaning Tower experiment works for everything (given similar aerodynamic properties).

Haven't we said, over and over, that the horizontal-turned-vertical momentum of a coaster train coming off the lift is completely negligible? You'd need something like the force of an S&S drop tower pushing down to make any considerable difference.

The only way to make the bullets land at different times is to fire the gun non-horizontally so that it has *some* vertical momentum

In free space, yes. The path of the fired bullet is parabolic. The path of the dropped bullet is a straight line. There isn't an external constraint on the motion of either bullet*---their motions are dictated entirely by their initial conditions at the point of firing/being dropped. And, at the initial conditions, both have a vertical speed of zero, and only once force (gravity) acting on them along that vector, so they hit the ground at exactly the same time.

(*: I'm ignoring friction here.)

The bullet is "constrained" by its horizontal motion (caused by the explosion behind it), but it's still pulled to earth at the same speed by gravity.

Sorry, by "constraint" I meant "external constraint". The horizontal motion is not a "constraint", it is the initial condition. And, in free space, there is no way for that horizontal kinetic energy to be redirected along the vertical vector.

In contrast, a coaster train's motion *is* subject to an external constraint: the track. If a train is "dropped" at the top of the lift hill, it's unconstrained motion would be "fall straight down". But, as it pushes down on the track after the chain disengages (i.e. just at/after the crest of the hill) the track pushes back, redirecting the train's motion forward. Likewise, if a train is "shot" forward at the top of the lift hill, it's unconstrained motion would be "fall to the ground along a parabolic path". If the parabolic path is shallower than the track (i.e. the train would otherwise go farther horizontally than the track allows) then it pushes forward against the track, and the track pushes back, converting some of that horizontal moment to vertical.

There is no equivalent motion-vector-redirection in the bullet example, which is why they hit the ground at the same time. There is no mechanism to convert the fired bullet's horizontal motion into vertical motion. However, it is important to note that the fired bullet traveled much farther in total than the dropped bullet. They each traveled the same distance vertically, but one traveled much farther horizontally. But, rather than firing/dropping the bullets in free space, suppose you had a tube, bent in the form of a quarter-circle. At the very entrance to the tube, the slope of the tube is perfectly horizontal. At the bottom, the slope of the tube is perfectly vertical, and it continuously changes from horizontal to vertical along its path. If you drop a bullet in the tube, it will reach the ground more slowly than if you dropped it in free space---they each have the same potential energy, but the bullet-in-tube must travel farther under the same total acceleration. Effectively, some of the gravitational force is "redirected" by the walls of the tube from a vector straight down to a vector with some forward component. Likewise, if you fired a bullet into the tube, it would hit the ground faster than if it had been fired in free space, because the tube constraints the otherwise-parabolic path of the bullet. Effectively, the tube applies an additional downward force on the bullet as the bullet pushes up against the tube.

Like our bullet-in-tube, a "fired" coaster train and a "dropped" coaster train must travel exactly the same total distance, both forward and down, from the top of the lift hill to the bottom, because the track constrains the path. But, because the "fired" coaster started out going faster, it arrives at the bottom faster. Again, though, the total speed imparted to any real coaster at the bottom of its lift hill by the kinetic energy at the top is negligible vs. the potential energy it has at the top of the lift hill, it probably doesn't matter in practice, and is almost certainly outweighed by all the other random variables in the course of a typical run.

In other words:

Haven't we said, over and over, the horizontal-turned-vertical momentum of a coaster train coming off the lift is completely negligible?

Yes, it is. It's not (technically) zero, but it is probably safe to ignore for any lift hill-like substance.

Jeff said:
Haven't we said, over and over, that the horizontal-turned-vertical momentum of a coaster train coming off the lift is completely negligible? You'd need something like the force of an S&S drop tower pushing down to make any considerable difference.

Yeah, but they won't do that because that ride ripped some girls hair out when she was stuck at the top.

~Rob

Speaking of chain speeds... reminds me of how much I like how my home parks' woodies - American Eagle and Viper, both have a pause at the top. It's almost a stop! It's great for anticipation (especially on the Eagles huge, ever-disappearing drop) and you can talk - look around, it's a real nice change from the usual up and over quickly.

There was something a long time ago about how the Texas Cyclone at Astroworld had it's lift slowed down considerably to reduce the ejector air time on that first drop (before the drop was re-profiled, twice). That would make a little sense, but still probably negligible.

I may have shared this before, but I can't remember exactly where.

A train gets its kinetic energy at the bottom of a hill from two pieces: the kinetic energy it has coming off the lift at the top as well as all the potential energy generated from the fall. Ignoring friction, the two equations are:

Lift kinetic: ½ * (mass of car) * (lift velocity)²
Potential gained: (mass of car) * (gravitational constant) * (height of fall)

What you really want to look at here is the percentage of final energy that comes from both of the components. Since (mass of car) is in both, it can be removed from the equation. So you're left with: ½(lift velocity)² vs. (g)*(height). (g) is a constant (-)9.8m/s.

So now assume that the speed of the lift in a booking 2m/s and the height of the ride is 25 meters. That means that ½(2)², or "2" parts, are coming from the lift speed. And (9.8)*(25), or "245" parts, are coming from the drop itself. So, using these numbers, 99.19% of the car's energy at the bottom of the hill is from the drop itself and just 0.81% is from the chain speed.

I remember an incident on Millennium Force, and, with over 200 rides on it this past season alone, I am somewhat familiar with the ride. :) (Reviewing notes) Friday, Sept 23, 2011, after two not unusual rides followed by a catch car problem, I was on seat 5.1 of the yellow train when it stopped about 4/5 up the lift for about a minute. We then proceeded slowly to the top (the anti-rowbacks were really loud) and went over. It was by far the slowest ride I've ever had on Millennium. Millennium Tony (former ride-op) also commented on how slow the ride was. Paging Rideman....