Sunday, June 22, 2008

Apple #324: G Forces

Long-time readers of the Daily Apple may remember that I like to watch Formula One racing. There was another race today in France. (Felipe Massa came in first. My favorite driver, Fernando Alonso, came in 8th, but at least he got a point.).

One of the things the TV broadcasters do during each race is to show you the race from one of the driver's perspectives with an on-board camera. So you're watching as if you're the driver, looking out over the nose of the car while it is going at incredible rates of speed along the track and whipping around corners.
  • Just how fast are they going? Well, in this most recent race, Kimi Raikkonen had the fastest lap with a time of 1 minute 27 seconds. That's how long it took him to drive once around the 4.411 km track (2.7 miles). That means, averaged out over the entire track, he was going just over 113 miles per hour in that particular lap.
  • Big deal, you say? Well, this isn't like NASCAR where the track is just a circle. These tracks have super-tight turns, sometimes switching left & right several times in succession (chicanes). So the driver has to down-shift and slow down to make it around those turns -- though without losing so much speed that the guy behind him can pass -- and then they speed up again in the straightaway.

This is what the track looks like at Magny-Cours, France, where today's race was held. Image driving that thing at an average of 113 miles/hour in your Honda or whatever it is you drive.
(Image from BBC Sport)

  • It's difficult for me to guess how fast they're going on the straightaway, because though the announcers will sometimes mention their speed, it's always in terms of kilometers per hour, and I can't convert from kilometers to miles in my head, on the fly. But if I remember right, on other courses, sometimes the fastest lap is around 180 miles per hour. That suggests to me that, during this race, the drivers were going at least that fast on the straightaways.
Here's an example of the onboard view. This is of Kimi Raikkonen driving through the streets -- yes, those are the streets -- of Monaco in 2008. You can see people standing on the other side of the barriers they have erected at the curbs. This is just a practice lap, not an actual race.

(You can also see this video is a higher-quality version here)

Okay, so you're watching the drivers manipulate their cars at these 120 mile/hour plus rates of speed on the course, from the point of view of the driver. In addition to this perspective, the TV station sometimes puts up a graphic that shows the G forces the driver is experiencing. It looks like a target with a great big G in the middle and concentric circles radiating out from it. On this target they put a dot, green as it's closer to the middle and red as it moves to the outside. This is supposed to show what it feels like to be the driver as the car is going around the turns and the force of the speed and the turn is trying to push the driver's body to the outside of the turn.

In addition to this pictorial representation, they also have a scale with numbers along it and as the G forces increase, a green bar goes farther up the scale. So you also get the G force in numerical terms as well as in a spatial representation.

Now here's my question. I sort of intuitively get what they mean by G forces. But what are G forces, exactly? And at what point do you say, Wow, that's a lot of force?

  • Just by standing on the surface of the Earth, gravity is exerting a force on you. The force of gravitational pull is expressed as 1G.
  • Any time you move, you have to accelerate in some direction or another, and you have to do so enough to overcome the force that gravity is working on you in order for you to move. This is true whether you want to move vertically, horizontally, or in any direction.

When you first begin to run, you have to work hard to overcome the fact that you were first at rest. While you are mainly feeling the strain of your muscles working, your body is also experiencing a slight increase in the G forces pressing against it.
(Photo from Kapunahala Elementary School's page about speed)

  • It's important to remember that it's not speed that creates G forces, but a change in the rate of speed -- accelerating or decelerating -- or a change in direction.
  • As you accelerate, your body experiences that change in force. But most of the time, you're not accelerating that much, maybe a micro-unit above the force of gravity (something like 1.00000001G), so you're not really aware of it.
  • It starts to become a big deal when the force of acceleration doubles or even triples the Earth's gravitational pull -- 2G or 3G.
  • But it's really only a big deal if those G forces are experienced over a significant length of time. If you jump down from even the lowest step on a flight of stairs, you're moving faster than the rate of gravity by 2 or 3G when you reach the floor, but you experience that level of force very fleetingly. The average sneeze creates a force of around 2.5G.
  • Sustained over time, however, at even 3G, most human beings will lose consciousness. During World War I, when people were sending pilots up pretty much for the first time, they discovered some of the pilots were "fainting in the air," and that's how they found out about G forces. It was decided that people could not withstand G forces more than 18G.
  • The reason people faint at higher G forces is because your heart has to work that many times harder to keep the blood pumping throughout your body. If your body experiences a blip of high G forces, your heart says, "Okay, I can handle that." But if your body is constantly getting buffeted by the force of continued acceleration, your heart has to keep working extra-hard that entire time. And after a while, it just can't keep up, you get less & less oxygen to your brain, until finally you pass out. Or something else in your body gives way.

Diagram showing that people can withstand higher G forces for different amounts of time -- and depending on their body's position. If you are reclining, your heart doesn't have to work as hard to pump the blood around. Thus the pilots can withstand higher G forces if they're lying down.
(Image from Combat Reform -- a huge page with tons of images, so beware of data overload)

  • When you ride a roller coaster, you're also feeling the effects of high G forces. But the coasters are built so that those G forces won't be sustained for any length of time. Or when you're in a commercial airplane and it's taking off or landing, you're feeling the effect of high G forces.

This woman is riding a roller coaster, looks like The Hulk, which is at Universal's Islands of Adventure in Orlando. This coaster reaches forces of 4.5Gs.
(Photo from WKMG Orlando

  • While we're on the subject of roller coasters for a moment, one driver said that because of all the G forces, driving an F1 car felt like riding on a roller coaster, your body getting slammed around in that same way, except you have to drive it.
  • Today's astronauts, who get propelled out of the Earth's atmosphere at insane rates of acceleration, have to withstand 3Gs of force for the whole time the rocket is shooting up into space. Astronauts on board earlier space crafts endured forces of 9G.
  • Fighter pilots, whose airplanes can also accelerate at ridiculous rates, also have to withstand high G forces for extended periods of time, and up to 9G when they pull a tight turn. I should note, though, that fighter pilots now also wear special anti-g suits that have additional pockets of air and are constricted around the legs to help keep the blood flowing, so that they don't have to worry so much about passing out.
  • Formula One (F1) drivers fall into third place in the category of people who typically experience high G forces over long periods of time. Typically, when F1 drivers accelerate out of corners, they're feeling G forces of around 1.5G to 2G. As they're going into and around the corners, though, the G forces often reach 4G, and up to 5G when they hit the brakes. Sometimes, when they have to decelerate very quickly, the G forces can even be negative. Somewhat surprisingly, negative G forces are even harder on the body.
  • At 5G, your head, which weighs about 10 pounds, feels like it weighs 50 pounds. You have difficulty moving your hands and feet, lifting your arms, and keeping your head up.

Pilot John Stapp enduring all sorts of changes in G forces as he made a 421-mph ride in 1954.
(Photo from Nova's page about G forces)

  • Since Ayrton Senna's death at Imola in 1994, F1 officials have required F1 race tracks to have more turns in them so that the cars would not be able to get up as much speed and thus be required to decelerate as much when they encounter turns -- in effect, lowering the G forces throughout the track.
  • While astronauts and pilots are experiencing a downward pull as their crafts propel them into the atmosphere, F1 drivers are going around, more or less, in a circle. So their bodies want to continue in that trajectory of the circle. But when the car changes direction, the driver's body gets thrown toward the outside of that circle. In addition, when the car slows down or speeds up, the driver's body is moves forward as the car is slows, or is pushed back against the seat as the car accelerates.
  • So the F1 driver's body is getting shoved around in all kinds of directions almost all the time they're racing. This is one of the reasons why you can see their heads kind of bobbling around in the car as they're driving. And the helmets they wear weigh about 14 pounds.
  • Lots of F1 drivers do specific exercises to strengthen the neck so they're better able to withstand all that bouncing around. In one program about F1 racing, I saw driver Jarno Trulli with a strap around his head which was attached by a cable to some weights on a weight machine. Sitting on the machine's bench, he tilted his head sideways, away from the machine, so that the strap pulled the cable and lifted the weights. I'm sure they all do similar exercises. Kimi Raikkonen's neck, for example, is looking more and more like a football player's.

Kimi Raikkonen, last year's Formula One champion, has been keeping up with his neck exercises.
(Image from

Here's another onboard view, this time with Fernando Alonso. This is the beginning of this year's race in Canada, and this gives you an idea of how fast these guys accelerate off the pole and how crazy it is at the beginning of every race as everybody's trying to get a better position and not crash. You can also see how much his head moves around as the car goes over bumps or around corners.

(You can also watch a higher quality version of Alonso's race here)

  • The effect on F1 drivers' cardiovascular system is even more significant. One study found that two drivers, who were averaging between 145 and 155 miles per hour in a given race, had their pulse rates go up to 175 to 200 beats per minute. Generally speaking, most people's pulse rates when at rest are around 60 to 80 beats per minute.
  • "It's extremely exhausting," says one member of the motorsport group at Cranfield University (UK).
  • Another driver said that because of the G forces, driving an F1 car is "like wrestling with King Kong."
  • When John Dixon decided in 2004 he wanted to try make the leap from Indycar driving to Formula One, he did pretty well in a test run, as far as keeping up with the rest of the pack, but he said the G forces in the corners were "huge." He went on, "The acceleration isn't too bad because your head is resting most of the time, but the g-forces turning and the braking in the braking zone, your head goes down and you have to slowly bring it up. The forces are way more than what we get. I lasted about three runs before my neck was done."

I have a couple other entries about Formula One racing, in case you're interested:
  • Formula One Racing - basic information about the sport, plus photos of leading drivers and some crashes
  • Nail-Biter - from 2006, in the midst of the season, around the time Schumacher announced his retirement, with one photo (I had others but they have since gone AWOL).

National Physical Laboratory, FAQs, "What are 'g-forces' and are they caused by gravity?"
Peter Tyson, All About G Forces, Nova
Argonne National Laboratory, Ask a Scientist Physics Archive, What is the greatest amount of g forces experienced?
M. Colleen Gino, Human Spaceflight, Astrophys-Assist
Ian Sample, "How grueling is formula one?"
The Guardian, March 3, 2005
Eric S. Watkins, "The Physiology and Pathology of Formula One Grand Prix Motor Racing," chapter 14,
Clinical Neurosurgery, Volume 53, 2006.
Formula One Drivers Fitness, F1 Complete, November 19, 2006
"Dixon keen on F1 move," BBC Motorsport, March 29, 2004

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