This high school teacher (formerly a worker at NASA) claims to have come up with a calculation for how it wastes less gas to have the air conditioning turned on versus rolling down the windows. I told my friend this teacher must be a complete moron, but my friend insists that I should "broaden my horizon." So, do you think this theory is pathetic or not?
UPDATE: I have not seen the calculations, but my friend says the teacher has come up with them. My point is that the theory is pathetic to begin with and therefore the calculation must be flawed too...
2007-07-18 06:24:04 · 7 answers · asked by Anonymous in Environment ➔ Other - Environment
You're talking about a moving car of course. The idea is that rolling down the windows causes more drag from the air.
It's a close call and depends on the exact car, speed, temperature, etc.
The teacher is not a moron, although the issue is not easy to calculate exactly.
2007-07-18 06:39:31 · answer #1 · answered by Bob 7 · 1⤊ 0⤋
If you are talking about a MOVING CAR, then it is not a new idea. He may have improved the calculations, but the idea is not new and not silly at all. The reason is aerodynamics. A car with the windows rolled down experiences more air drag than one with the windows rolled up. And drag increases as the square of the speed. That means twice as fast results in 4 times as much drag, not only twice as much. So at some speed, the extra power the engine has to produce to overcome the extra drag and keep the car going at that speed is more than required to run the air conditioner. The usual statements are that at freeway speeds, drag is more of a load than the A/C, but in slower city driving it is less.
2007-07-18 06:37:28 · answer #2 · answered by campbelp2002 7 · 2⤊ 0⤋
Well the Mythbusters tested this
From wiki:Tests were performed under varying conditions (55 mph versus 45 mph). Also, the 55 mph test was using a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient. This experiment--or one like it--is sometimes cited by the Magliozzi Brothers on Car Talk when presented with this question.
The theory is that keeping windows down increases drag, and its partially true, but as to whether this decreases fuel comsumption as much as running the ac, its close
2007-07-18 06:33:40 · answer #3 · answered by MLBfreek35 5 · 2⤊ 0⤋
I recall a related study from a few years ago that indicated at slower speeds it's more efficient to leave the windows down, but at higher speeds the impact of drag on fuel efficiency increases beyond the loss of fuel economy due to the AC. I think the threshold varied from model to model but was in the 45 MPH range. Sorry, I don't have link for the study.
2007-07-18 06:40:57 · answer #4 · answered by gergreg 2 · 1⤊ 0⤋
I think the teacher is absolutely correct! Think of aero-dynamics, and how much pull you are putting on your car by keeping the windows down. I actually have a very gas efficient car, and get worse gas mileage in the spring than in the summer when I use my AC.
2007-07-18 06:34:03 · answer #5 · answered by Ann D 3 · 1⤊ 0⤋
He is right you are wrong.
There is a threshhold however:
At speeds below ~35mph its more fuel efficient to leave the windows down. However at speeds above ~35mph the fuel economy is better with the windows rolled up.
Its all about air drag and aerodynamics man.
2007-07-18 06:48:26 · answer #6 · answered by Anonymous · 1⤊ 0⤋
It's been proven experimentally. Get going 50 mph and think of all the drag on the car with open windows compared to when its windows are closed
2007-07-18 07:12:48 · answer #7 · answered by Gene 7 · 1⤊ 0⤋