How does air movement across a surface result in lift?

Targets

At the end of this Unit you should be able to answer the following questions 

2. What forces are involved in flight?

2.1 How do flying devices and living things counteract gravity?

2.2 How does air movement across a surface result in lift?

2.3 How can drag be reduced?

2.4 What means of propulsion are used in aircraft?

targets

What goes up must come down – or does it? We know that gravity is a force that is acting on Earth all the time to pull things down. But, you also know that there is more than one force working to keep things in the air.

Lift refers to the force acting upwards, against gravity, that is produced by changes in air pressure, or air currents.  This phenomenon does not happen by accident.  It is produced and maximized by certain shapes that direct the flow of air currents to produce the greatest amount of lift.

Lift is the reason an albatross can glide for hours without flapping its wings.

The albatross is a bird that can glide in the air for hours without stopping or even flapping its wings. In fact, rarely is it seen on land. It has the largest wingspan of any bird – up to 3.4 metres (11 feet). The wings are adapted to allow this bird to glide for hours on the wind currents coming from the sea.

  Video

Albatross Video

Watch this short clip of the albatross flying, and consider what must be happening to allow the bird to stay in the air.

The albatross appears to be doing nothing, but air currents are passing over its wings the entire time. Meanwhile, the bird makes small adjustments to wings or tail to direct the air currents in the best way to either rise or fall, or even turn itself while in the air.