Title text:
I understand it’s hard to do more than 300 feet on these 90-second rush jobs, but with a smaller ramp I’m worried the gee forces will be too high for me to do any tricks.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3152/
skamtebord
Do a kickflip!
Now I want a “what if?” on this. I would love to see all the g-forces and wind resistance and other details of how to survive with a big ramp.
I started to answer this, began breaking out the calculus and the kinetics equations, and then said to hell with it. As a really, really simple answer: Average fall rate for a human that knows how to skydive is going to be somewhere around 100-120 mph. I think I average about 118, per the little app I have, but the phone’s sensors probably aren’t really all that great for accurate measurements about it. If a person could sustain two Gs (give or take 40mph/s) vertically for the length of time needed, three seconds, and that your velocity was entirely conserved (I know, I’m throwing out wind resistance here), that would mean a ramp transition distance of ~540 feet (not really accurate, because mph converts to feet per second at 1.47, not 1.5, but easier math here). If it’s a quarter pipe it’s not a perfect circle’s arc (and especially not, because you’d also have to have a consistent normal force with a vertical vector of two G but I don’t actually know their measurements and calculating the angle needed to give a vertical component of 2G at each second is beyond me right now) so I’m just going to peg it as a 90 arc of a circle, which would then have a circumference of 2160 ft, which gives us a diameter of ~687.5696 ft, and a radius (which would be the height of the ramp) of ~343.7whatever ft.
So to get 600 ft. maybe our intrepid hero calculated his sustainable G force differently, or the angles make for a much longer rampe vertically, or maybe wind resistance and the loss of energy due to friction and other small influences on the wheels and bearings and such would have a bigger bearing on him.
Edit: Also, grumpy grunt here: no one could confuse anything for their skydiving rig. Those things take a fair bit to get into, and the folks letting you on the plane would also have a pretty good idea that you’ve fucked up if you try to bring a skateboard thingie into the plane on your back. You put those things on on the ground, with plenty of time to check out the various parts to ensure they’re in working order.
For safe deceleration, you can only decelerate at a constant rate of about 3 Gs before things automatically become dangerous for the average person. They’d be moving at about 120-150 mph. Let’s say 135 mph, or 200 feet per second. Decelerating at 3 Gs, they’d need a half pipe with a smooth curve about 7 seconds, or 840 feet per quarter circle (half-halfpipe).
Now this is where I’m not sure, are half pipes smooth half circles? If they are, then you’d want a half pipe with a radius of like 535 feet. If not, then I’m stumped. Any skaters with input?
