BR physics chapter 7 passage 6 number 42

[2010premed]

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A uniformly accelerating plane will take off in the shortest time, if it flies:

Against the wind

can someone explain please?

 

[collegestud2013]

A uniformly accelerating plane will take off in the shortest time, if it flies:

Against the wind

can someone explain please?

If it accelerates against the wind the velocity difference between the plane and the wind will be the greatest, thus leading to a greater difference in air pressure and a stronger force to "push" the plane into the air sooner.

 

[fizzgig]

more air over the airfoil = more lift. it is uniformly accelerating whether it is into or away from the wind - keep in mind they're not saying it doesn't take more power to do this, but assuming you take off into the wind and have the same acceleration profile as taking off with tailwind, you're forcing more air over the airfoils.

put another way your groundspeed is the same for both, your airspeed is greater if you're into the wind.

 

[Pamplemousse123]

A uniformly accelerating plane will take off in the shortest time, if it flies:

Against the wind

can someone explain please?

I still don't get it! Explain to me why the answer is not with the wind. My reasoning is that if an airplane goes with the wind there's more velocity and thats more of a pressure differential (?) required to lift the airplane.

Please explain!

 

[BerkReviewTeach]

I still don't get it! Explain to me why the answer is not with the wind. My reasoning is that if an airplane goes with the wind there's more velocity and thats more of a pressure differential (?) required to lift the airplane.

Please explain!

Both answers above are excellent physics answers that apply Bernouli's principle. If they aren't making sense, you may want to take this time to make a short list of glossary terms and see if that helps.

It may also help to think about a real life example. If you've ever flown a kite in the wind, you know that if the wind is blowing against the bottom of the kite, it catches more air and gets pulled up with ease. This is the force of the wind against the bottom of the kite being greater than it is against the top of the kite. The same is true of the plane. Planes are designed to catch more air against the bottom of the wings as they travel forward (you can't fly a plane backwards). Like fizzig and collegestud2013 have pointed out, this creates a greater pressure difference between the bottom and top of the air foil, generating greater lift.

Hopefully this helps.