Monday, April 25, 2011

Techie Tuesday - The Hill & The Blow

As anyone whose ever aspired to being a pilot, and taken ground school knows, wind never helps you. It always hurts you. The same is true for gravity. This is why both wind and hills slow you down. Let's look at some examples.

Assume there is a route from point A to point B that takes an hour to ride in calm conditions. Now assume there is enough of a headwind that it takes 1 hr and 59 minutes to get from A to B. How fast would you have to return from B to A to match your total ride time in calm conditions?  Yeah, really, 1 minute! So what if the wind had been just a bit stronger? It would take you longer to get to B than the round trip in calm conditions.

How can this be? The wind is blowing exactly the same speed when helping you as when hurting you, so why does it slow you down so much? The answer is simple. The wind is hurting you for a lot longer than it's helping you, and the stronger it is, the more this is true.

Like wind, the force of gravity is also a constant force applied over time (you can't crank it up or down), but when climbing a hill the force of gravity is hurting you for much longer than it helps. On really steep climbs, 10X as much.

This is also why a steady diet of rollers is so exhausting. You're spending almost all of the ride time fighting against the added force of gravity. Look at a route full of rollers on a Garmin trace, and pick time as the X axis, instead of distance. It looks like a sail pattern, not a series of upside-down Vs.

NASA uses the force of gravity the same way to slingshot satellites around planets. The satellite approaches slowly, so the force of the planet's gravity has a lot of time to pull on it, but when it passes the planet, it is really moving, so it quickly escapes the pull of  gravity.

In all of these cases, it's the TIME the force is applied that is key. Just thought you'd like to know.


Gotta Run..Gotta Ride said...

And like always... you leave me thinking and pondering.....

Grey Beard said...

Ground school 101 Robin. It's on the FAA license exam, and covered in the first 5 chapters in every study guide ever published. Sort of mental cross-training to apply this to cycling.