Retarded rednecks don't know physics(Slingshot)

[Academia Nut]

So I was browsing about YouTube when I discovered this wonderful display of future Darwin Award winning behaviour. Even those people in Britian with the human trebuchet had the foresight to put on some protective gear

What is really interesting is that someone of our own heart posted a rebuttal where he derived out using basic Newtonian Kinematics just exactly how stupid those idiots were being with their slingshot. What is perhaps most depressing is the comments to his video and the appaling lack of respect he gets, although he takes it in stride.

So, anyone else know of some retardation on this level? Or was it one of you that derived out the whiplash causing acceleration and then called a spade a spade?

[Feil]

It would be somewhat more accurate to evaluate this with a constant delta-acceleration, rather than with a constant delta-velocity. Mass is constant, but force would be changing from maximum force to zero as the rider approached the point of zero potential energy--as anyone who's pulled a rubber band knows, it's easier to move it the first few inches than the next few inches, and so on. This would put the rider's acceleration at the extrema of her path at 10.6 Gs, not 5.3.

The only reason the rider avoided whiplash is that her spine was not held immobile (as with a seat-back or seatbelt); her spine bent, not just her neck.

As any number of people have said, this was criminally stupid.

[Wyrm]

Awright, let's assume the lady's motion is constrained to one dimension, x, and assume bodybager is correct in saying that she went from 104' (31.7 m) back through the center in 1.1 seconds.

First, let's assume that the bungees are simple springs with spring constant k/2, and the poles are placed a distance 2a apart. Let x be the lady's displacement from the center of the poles. The amount of stretch the bungees are under is h = \sqrt{a² + x²}, so the bungees are each exerting a force of F = -kh/2 along their length. The force in the x-direction is F_x = F cos θ. But cos θ = x/h, and there are two of them, so F_x = -kx.

The force on the lady is F = -kx in our x axis. By Newton's 3rd, F = ma, so ma = -kx, or d²x/dt² = -ω²x, where ω² = k/m. This second-order differential equation is an old friend, and has the general solution x = A sin ωt + B cos ωt.

Now we apply our boundary conditions:

x = 31.7 m @ t = 0 s
x = 0 m @ t = 1.1 s

Therefore we find that ω = (1.1 s ∙ π/2)^{-1}, A = 0 and B = 31.7 m, so x = B cos ωt = (31.7 m) cos t/(1.1 s ∙ π/2)

How fast is the girl going when she reaches the center of the slingshot? Well, that's the first derivative of the equation of motion we just found, evaluated at t = 1.1 s: dx/dt = -Bω sin ωt, and when t = 1.1 s, dx/dt = -Bω = -18.34 m/s = 60.19 ft/s = 41.03 mi/hr. Still a pretty good clip, but not the 128 mi/hr claimed.

The maximum acceleration is experienced at t = 0, where the second derivitive of x is d²x/dt² = -Bω² = -10.61 m/s², which is of course, barely over 1 g, not the 5.3 g's (or Fiel's 10.6 g's) claimed.

Here's the sanity check: turn your head 90° to the right and watch the film. Looks like a normal fall, doesn't it?

This is no more stupid than a normal bungie jump... which I still consider to be pretty stupid.

EDIT: I fail so hard. The boundary conditions fix ω = π/(2.2 s), which changes everything.

v_max = -45.26 m/s = 101.3 mi/hr.
a_max = 64.64 m/s² = 6.5 g's

So the maximum speed of the girl isn't as high as bodybager's, but still more than twice my original estimate. Also, the original acceleration is way off. Not as high as Feil's, but higher than bodybager's.

Sheesh. So much for my sanity check.

[Zaia]

Am I missing something? Why is this in AMP?

[Academia Nut]

I'm sorry, I haven't been thinking straight for the past few days due to a cold, so I don't really know why I did put this here . Please move it if you feel it is inappropriately placed.

[Mr Bean]

Thread moved, title updated.

[Kuja]

Holy shit. At first I thought that they were actually going to launch her somewhere and I thought "you've got to be fucking joking." What actually happened is still damn stupid but not nearly as bad as my first impression of what was going on.

[Teleros]

Meh, if they'd launched her I'd've just put her down for a Darwin Award .

[CaptainChewbacca]

There's a similar ride at the county fair, though with nowhere near this sort of accel.

[fusion]

Even at ten Gs, the accel is not that bad because when you land after a jump is ten Gs. Also it is not that bad because the time that she experience the Gs over five is only for less than a second. Gs are only dangerous because of time, humans can exprience fifteen Gs without blacking out but only for a very short time. A roller coaster called Zonga in six flags Marine World used to have six G loops before it came to America; it now has five G loops due to modifications of the loops.

[Singular Intellect]

Correct me if I'm wrong, but really, isn't the only really dangerous part of the event the initial acceleration?

After that, at both ends your speed and momentum is being slowed considerably before you begin getting pulled the opposite way.

[petesampras]

Even at ten Gs, the accel is not that bad because when you land after a jump is ten Gs. Also it is not that bad because the time that she experience the Gs over five is only for less than a second. Gs are only dangerous because of time, humans can exprience fifteen Gs without blacking out but only for a very short time. A roller coaster called Zonga in six flags Marine World used to have six G loops before it came to America; it now has five G loops due to modifications of the loops.

I think the concern here is neck damage, rather than blacking out. If your neck is unsupported it takes far lower Gs to screw it up than is needed to make you black out.

[Lost Soal]

My concern would her smacking into the ground on one of the back swings. That and the elastic snapping of course.

[aerius]

Correct me if I'm wrong, but really, isn't the only really dangerous part of the event the initial acceleration?

No, the really dangerous part is when gravity & aerodynamics change the axis of the motion and smacks her right into the ground.