5 ms·
As a kid in a car, when I stuck my arm straight out the window at speed, it got pushed backwards (in my frame) by the airflow. Keeping the arm rigid took effort
by 8bitsrule 5y ago
As a kid in a car, when I stuck my arm straight out the window at speed, it got pushed backwards (in my frame) by the airflow. Keeping the arm rigid took effort. If I tilted the front of my hand in a clockwise direction, my arm was pushed upwards. It took more effort (rigidity) to stop that considerable force.
That's the observation. Clearly my rigid arm/hand was accelerating some air downward. Like a gun accelerating a bullet, there's a recoil (but a continuous one). That's Newton: conserving momentum. Maybe not a complete explanation, but it's the bulk of one.
Here's how NASA puts it:
https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
- ec109685 5y agoThat only (intuitively) explains lift generated by a positive angle of attack. As shown here, you can get lift with a flat angle of attack: https://www.wolframalpha.com/input/?i=NACA+6409+airfoil&assumption=%7B%22F%22%2C+%22AirfoilAngleOfAttack%22%2C+%22a%22%7D+-%3E%220%22 https://www.wolframalpha.com/input/?i=NACA+6409+airfoil&assu...
- smusamashah 5y agoThe upside is curved pushing air upwards reducing the pressure hence generating lift from below. Isn't it just that?
- hollerith 5y agoIf the plane is pushing the air up, then by Newton's third law, the air is pushing the plane down. Also, pushing it up would not reduce the pressure of a parcel of air.