Skip to Content Go to sign in Skip to Primary Navigation Skip to Page Navigation Skip to Header Navigation Skip to Footer Navigation Toggle Accessibility Options or learn more about accessability

Physics Classroom is making strides to make our site accessible to everyone, and features many accessibility features.

Our site contains 6 navigation areas. The Primary, Secondary, and Page Level navigations have a screen reader version of their nav structure that allows using the left and right keys to navigate sibling navigation items, and up or down keys to navigate parent or child navigation items. The others can be navigated using tabs.

Within the main content, we leverage headers to provide in page or in tool navigation.

Although we are still rebuilding our content to leverage these tools, our images should have both short and verbose descriptions, the later describing in great detail the image for those who cannot see. Any formulas found within the images are often in the image figure below the image.

Equations and formulas are rendered using MathJax, which has both verbal, braille (including nemath braille), and keyboard navigation within them. Learn how to configure and leverage this for various screen readers on our Equation Navigation Page.

While not every area of Physics Classroom is usable purely from keyboard and screen reader, we are committed to continue work on making this possible. If you have questions or need additional help, please use this link to contact us .

Return to screen reader navigation

Skydiving

Observe the motion of the skydiver below. As the skydiver falls, he encounters the force of air resistance. The amount of air resistance is dependent upon two variables:

  • The speed of the skydiver

    As a skydiver falls, he accelerates downwards, gaining speed with each second. The increase in speed is accompanied by an increase in air resistance (as observed in the animation below). This force of air resistance counters the force of gravity. As the skydiver falls faster and faster, the amount of air resistance increases more and more until it approaches the magnitude of the force of gravity. Once the force of air resistance is as large as the force of gravity, a balance of forces is attained and the skydiver no longer accelerates. The skydiver is said to have reached a terminal velocity.
     
  • The cross-sectional area of the skydiver

    A skydiver in the spread eagle position encounters more air resistance than a skydiver who assumes the tuck position or who falls feet (or head) first. The greater cross-sectional area of askydiver in the spread eagle position leads to a greater air resistance and a tendency to reach a slower terminal velocity. The importance of cross-sectional area to skydiving is also demonstrated by the use of a parachute. An open parachute increases the cross-sectional area of the falling skydiver and thus increases the amount of air resistance which he encounters (as observed in the animation below). Once the parachute is opened, the air resistance overwhelms the downward force of gravity. The net force and the acceleration on the falling skydiver is upward. An upward net force on a downward falling object would cause that object to slow down. The skydiver thus slows down. As the speed decreases, the amount of air resistance also decreases until once more the skydiver reaches a terminal velocity.

Skydiving Animation

For more information on physical descriptions of motion, visit The Physics Classroom Tutorial. Detailed information is available there on the following topics:

Newton's First Law of Motion

Newton's Second Law of Motion

Free-Body Diagrams

Free Fall vs. Air Resistance
 

Return to List of Animations

Return to Screen Reader Navigation
Tired of Ads? Go Ad Free ($5/year))