Why wind is a blow to record seekers

By Burkard Polster and Marty Ross

The Age, 15 July 2008

If you can run 100 meters in less than 9.72 seconds then you can claim the world record from the current holder, the aptly named Usain Bolt. But of course your time won’t be considered if you’ve run with a huge tailwind assisting you. The rules state that a time is disqualified for a record if the tailwind exceeds 2 m/s. The same rule applies to all athletics events that involve moving essentially in the one direction.

That makes sense, but what about for circular events, such as the 400 meters? Did Cathy Freeman have to worry about wind-assistance? The answer is no: there is no wind-assistance rule for circular events. This also seems reasonable. Intuitively, the wind will help on parts of the track, and will slow you down on the opposite parts, and overall the effects should cancel out.

The surprising thing is, our intuition is not quite right. In fact, if there is any wind it will slow Cathy Freeman down overall: she should have bonus seconds deducted from her time.

Let’s look at a simpler situation. Imagine a pigeon race with a pigeon flying from Melbourne 200 km North to Echuca, and then back again. If she flies at 100 km/h then the round trip will take 4 hours.

But suppose that a Southerly wind of 50 km/h is blowing towards Echuca. On the way to Echuca the pigeon can travel at 150 km/h, and then some simple arithmetic shows that the first 200 km leg of the trip takes 4/3 of an hour, or 80 minutes. However, on the way back the pigeon can only travel at 50 km/h, and so the second leg takes a full 4 hours. So, the total “wind-assisted” roundtrip takes an extra 80 minutes.

How to explain this puzzling result? The distance traveled is the same in either direction, but obviously the time fighting against the wind will be greater than the time being assisted by the wind. So, the resistance has more effect than the assistance.

Perhaps even more surprisingly, the same is true for any race on any loopy racetrack no matter the shape. Wind always hurts. True, Cathy Freeman is less affected by the wind than a racing pigeon, but the nature of the effect is the same. So, if you’re out to break the 400 meters world record, make sure it is a calm day.

There is at least one exception to this rule. If you can arrange to have a little tornado centered in the middle of the track, then you should be able to manage a terrific time. And, there’s nothing the record-keepers can do about it.