# Video: The Physics of Kelly McGarry's 72-Foot Backflip

Oct 13, 2015 at 9:36

RED BULL

RAMPAGE

The Physics of Kelly McGarry's 72-Foot Backflip

Title image by Nathan Hughes.

MENTIONS: @redbull.com/rampage / #rampage / @redbullbike

• + 163
That is what physics class should be like! Less text books, more rampage case studies!
• + 16
urgh i hated case studies!
• + 118
• + 89
Well I'm a physics teacher, so I was looking forward to using this in my class. It's just a shame that it teaches nothing, and they got their calculations and units wrong.... More high quality content from the good folk that brought you the red bull video player.
• + 9
Was thinking the same blahblahbikes. I'm not sure if using the phrase "the totality of the run" offends me more or if "FPS" being feet per second does
• + 2
@blahblahbikes as an engineering student I immediately suspected this might be the case and came straight to the comments so that I wouldn't have to waste my time watching it
• + 6
Still worth watching if you like bikes.
• + 5
@blahblahbikes, shouldn't be too hard to adapt into a cool problem for your students to solve though...
Just have them calculate launch speed needed to clear X gap or how ramp angle affects their trajectory or what if Kelly started binging on burgers until next Rampage and put on 100lbs. Lot's of stuff you can do to make a simple projectile problem a lot cooler.
• + 3
@blahblahbikes @fefillo @CameronRose to build on that, its an add on to a typical projectile motion question after a conservation of energy question:

take off at 11deg,
gap: 72ft
A) determine required launch speed

initial y: +91ft
B) assuming no energy is lost, must he brake tap?

C) assuming the landing is symmetrical to jump (169deg from horizontal), compute rotational spin for one flip (in rpm)

D) explain why a front flip has a higher rotational spin than a backflip
• + 86
Still think he should have won that rampage
• + 18
He won the fan choice thing, so that's something.
• + 10
So did most people. I thought the podium was way off.
• + 7
The guy is a Smiley Faced Beast...can't help but cheer hard for him!!!
• + 61
They can work out all those numbers and do fancy editing, but they still haven't gotten around to fixing the woeful redbull video player.
• + 29
Downvote me if you want, but after watching this it almost seems logical to have speedometers on the bike. maybe HUD on goggles?
• + 3
but now that I think about it, is there any way to increase your speed to make it matter? I guess you could throttle back if you are aimed for an over-shoot.
• + 6
• + 2
Too bad Google Glass was so dang expensive! I was invited to spend \$1500 for my developer preview, passed along to every coder buddy I know and nobody wanted it at that price. There could be some sick applications with it though.
• + 1
and if you are to slow you can't do anything
• + 1
A company is working on a display called Gogglepal. There are a couple of different models but I think they start at around 150 USD. Still in preorder. Built for skiing but I don't see why they wouldn't work for mountain biking.
• + 5
Speed is only one factor, squashing or extending on the eject makes a big difference
• + 2
It already exists. Check it out: www.reconinstruments.com
• + 20
That's great stuff, but can we get a metric version please?
• + 11
With proper English language too!
• + 10
And proper math too!
• + 6
Was thinking this too.

Imperial Units are such bullshit. So f'king stupid imo.

A simple example:

How many feet are in a mile?
How many meters in a kilometer...
• + 2
40 mph is 64kmph 72ft is 22m Having no real concept of what the imperial measurements looked or felt like this puts in it into perspective of just how fucking gnarly it was.
• + 13
History... Until Zink's flip
• + 2
and even ... these days it's pretty usual to backflip the canyon gap (multiple attempts and succeeds last year..)
• + 5
Different gap.
• + 9
"As he spots the landing, he stops the rotation to match its angle" I've never done a backflip in my life, and never will, but I'm pretty sure you can't stop your rotation? Otherwise no-one would ever overrotate a flip?
• + 16
Right. You just slow down your rotation by opening up
• + 4
You can sort of dude slow down your rotation by opening up meaning stretch out make your body/bike bigger an to speed the rotation up it's the opposite make your body/bike small if that makes sense dude..??
• + 3
You can't completely stop your rotation but you can put your body in a position that isn't encouraging rotation so you can land properly.
• + 2
He changes his body position to slow down / stall his rotation - but yes, its still ulitmatley down to sheer skill, timing/co-ordination and balls sthe size of jupitor!
• + 9
Let's try to explain this properly...... When you rotate you have angular momentum, which is a product of how widely distributed your mass is and how fast you are rotating. If you concentrate your mass more, for example by pulling yourself closer to your bike, you will rotate more quickly. If you do the opposite, as in extend your arms and legs to push your bike further away, you will rotate more slowly. So, you can slow down your rotation to land a flip safely. You can't stop rotating completely; if you try, you'll turn into a gnome.
• + 1
you still could hit the rear brake to slow a little more
• + 2
A way to experience this concept is to try it on an office chair. Spin the chair while sitting on it and extend your arms and legs then proceed to bring them close to your body. You will notice the change in angular velocity.
• + 2
Ballerinas have known this for ages... try ballet mother F...
• + 2
Everyone has known this for ages. It's basic physics.
• + 1
Conservation of rotational momentum.
• + 4
amazing... McGarry showed what is possible and one year later it was a "piece of cake" for several riders and Tom van Steenbergen almost succeed his frontflip attempt. What a progress for "our*" sport. ("our*" because they are a league for their own)
• + 4
So he in order to clear the jump he has to be at 40 miles per hour but the guy says he lanches off the ramp at ALMOST 30 feet per second. 30 feet per second is 20.45 miles per hour...someone needs to go back to math class...
• + 1
He had to be going somewhat slower off the lip, because going up the ramp trades some speed for some altitude. Or trades some kinetic energy for potential energy, if you prefer. Losing half of his speed seems a bit much, but I'm too lazy to do enough math to say for sure.
• + 6
still cant believe a suicide no hander won over this 1 of three backflips in his run. Robbed
• + 4
Just realised how pointless that canyon gap must be most days around the year
• + 3
But do they actually do the math, or is it just hmmm, that looks about right and speed is your friend.
• + 2
I always wonder the same thing. Ken Block said he used an archery app to figure the speed and takeoff angle he needed for some of his jumps, but I've never heard of a biker talking about anything like that. Given the consequences, I'm surprised someone hasn't built a radio-controlled contraption of some kind to check their math before they drop in. But then I have trouble judging my speed for ten foot gaps, so I just can't imagine eyeballing the run-in to a 50-footer and having any clue about where I'd land... You obviously won't be seeing me at Rampage any time soon. Unless someone's radio-controlled guinea pig needs a driver.
• + 3
This video shows how cool this trick was but also how close he was to complete disaster if he came up a foot or two shorter.
• + 1
Why was the landing to a 72 gap jump so damn sniper? I counted 4 bike lengths, seems ridiculously short, but then again I don't hit jumps that big so what do I know?
• + 4
Well that was neat!
• + 3
What about the other two flips? That first flip he did was crazy!
• + 1
Should have won it , but except that ,wow this is getting serious and dangerous ,but at the same time exciting ,strange :-(
• + 1
awww snap! i can see me in that video sitting down there below the flip like, OHHHHH SHIT!
• + 2
More edits like this please.. this is bling!
• + 1
youtu.be/p4_YeAP9lac This is Kelly Mcgarry riding down in his home town, Queenstown NZ
• + 1
1 mph short and you're 4ft short, its more difficult than i've always thought
• + 1
oh that rhymes
• + 1
only kiwis can do that......
• + 1
how bout some Newtons? those are good.
• + 2
Can't they use metrics ?
• + 2
Even in switching to metric the numbers don't add up!
• + 2
• + 2
Cant wait...
• + 1
Well, I sure wouldn't say no to a heads-up display in my goggles.
• + 1
thank god for Phys. 101 with Sister Cristopher back at Kennedy High.....
• + 1
I'm about finished with that rock band commercial.
• + 1
i see me!
• + 1
potential injury LOL
• + 0
{deleted comment that was meant to be a reply}
• + 0
{just ignore this}
• + 1
RIP