What is air resistance? - R

What is Air Resistance
By Grace W.
2012

It takes force to push an object through a fluid. Jet airliners need very powerful engines. The resistance to movement is called drag, and streamlining is one way of keeping drag as low as possible. What is lift? Take an airplane. How does it fly exactly? An airplane has airfoil surfaces. An airfoil surface is slightly more curved over the top than beneath, such as an airplane wing. This results in a pressure difference as the wing moves through the air, producing lift.Figure #1: an airfoil wing

Aerodynamics and reducing lift force

Aerodynamics is the study of airflow and its principles. Builders design there race cars for negative drag, and negative lift, because the faster the car goes, the greater the lift force, which increases the threat of instability. Among the design features most often used to decrease drag while achieving negative lift is a rear deck spoiler. The race car has an airfoil shape but its purpose is different. It is meant to raise the rear stagnation point and direct airflow so that it does not wrap around the race car’s rear end. Instead, the spoiler creates a downward force to stabilize the rear, and may help to decrease drag by reducing the separation of airflow at the rear end window. The airfoil shape is also used to reduce air resistance, by having the air easily flow over the surface.

 Figure #2: reducing lift force and aerodynamics

The parachute-an example of air resistance

The parachute is a good example of air resistance, because they are meant to increase it. Parachutes use the science of drag resistance. Take sky diving. With no parachute, the person plummets to the ground at 120 miles per hour! But when they open the parachute, it’s a whole different story. The airflow around the parachute creates drag, slowing it down dramatically, so the person can make a soft landing. A parachute in use resembles an open umbrella. The open end is directed downward. Strong forces produced by air resistance push upward against the descending parachute. These forces oppose the downward pull of gravity. Although gravity's force is reduced, it is not completely eliminated. The speed of fall, however, is decreased from a speed of 120 mph to much safer 14 miles an hour.

 Figure #3: parachuting man

Glossary:

Coefficient: a number that is constant for a given substance, body, or process under certain conditions, serving as a measure of one of its properties
Density: mass per unit volume
Gravity: a force that constantly pulls to the ground
Relative velocity: the relative speed of an object
Viscosity: stickiness

Citations:
Knight, Judson. Science of everyday things. Detroit: Thompson/Gale. 2001.

Lewis, Peter. Facts at your fingertips introducing physics matter, energy, and heat. Tucson: brown bear books. 2010. Print.

"parachute." Compton's by Britannica. Encyclopædia Britannica Online School Edition.
Encyclopædia Britannica, Inc., 2012. Web. 24 Sept. 2012.
<http://school.eb.com/all/comptons/article-9276277>.

Smash Lab: Ejector Boat Seat Discovery Channel, 2007. Full Video.
Discovery Education. Web. 24 September 2012. <http://www.discoveryeducation.com/

Stanbrough, JL. Air resistance. batesville.k12, November 4, 2007. Web. 9/27/2012