Strictly speaking, a force is a Newton, or a kilogram·meter per second per second. In practice, a force is a push, a shove, a lean - anything that you do to cause motion. Without forces, you couldn't pick up your books for school, type on a keyboard, or jog on the sidewalk. Forces are what cause motion.

In flight, there are four basic forces, responsible for a plane's flight through the air. Those are:

• Lift - the upward force on a plane's wings, causing it to maintain altitude.
• Weight - the same weight as on you as you stand, opposing lift, and pulling the plane downwards.
• Drag - the many forces which combine to slow a plane down, taking away its speed.
• Thrust - the force propelling a plane forward, opposing drag, and keeping the plane at its intended speed.