air pressure: The force exerted by the weight of air molecules.
birds: Warm-blooded dinosaurs with wings that first showed up at least 150 million years ago. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
engine: A machine designed to convert energy into useful mechanical motion. Sometimes an engine is called a motor. (in computer science) A computer program that performs a particular, narrow range of functions.
flaps: (in aeronautics) These devices are attached to the back edge of an aircraft’s wing. It increases the lift force on that wing in addition to a frictional drag force (which can be especially useful at low speeds, such as in landing).
force: Some outside influence that can change the motion of an object, hold objects close to one another, or produce motion or stress in a stationary object.
gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
horizontal: A line or plane that runs left to right, much as the horizon appears to do when gazing into the distance.
lift: An upward force on an object. It may occur when an object (such as a balloon) is filled with a gas that weighs less than air; it can also result when a low-pressure area occurs above an object (such as an airplane wing).
perpendicular: An adjective that describes two things that are situated approximately 90 degrees to each other. In the letter “T,” the top line of the letter is perpendicular to the bottom line.
physics: The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
pressure: Force applied uniformly over a surface, measured as force per unit of area.
vertical: A term for the direction of a line or plane that runs up and down, as the vertical post for a streetlight does. It’s the opposite of horizontal, which would run parallel to the ground.
