# Lesson 02 – Taking Flight

## Vocabulary

Lift

Lift is the force that acts against the plane’s weight and holds it in the air.

Drag

Drag is the force, like friction, that pushes against an object to slow down its movement or pull the object backward.

Thrust

Thrust is the power or force that overcomes drag and weight to move an object forward.

Weight

Weight is how heavy or light something is.

Pressure

Pressure is the act of one force pushing against or pressing down on another force or on an object (e.g., when pressure is applied to a wet sponge, the water comes out).

Force

Force is a push or pull that slows down, speeds up, or presses on an object as it interacts with its surroundings.

Friction

Friction is a force created by one object rubbing against another, which acts to slow down movement.

Gravity

Gravity is the force that attracts objects toward one another (e.g., gravity pulls objects toward the ground).

## Taking Flight

Find out about the four forces of flight: lift, weight, drag, and thrust.

## Just a Little Lift

Lift helps an airplane overcome its weight. Lift also helps the plane rise into the air, and stay up in the air. Many parts of a plane work together to create lift. Most lift is generated by the wings.

Look at a bird’s wing when it is flying. You will see that it curves so that the top side is longer than the bottom.
Planes create lift in the same way.

Air moving over the curved wing top goes farther than air going under the wing. The air also moves faster. Air that is moving more quickly exerts less pressure. So the air below the wing pushes up harder than the air above the wing pushes down. That lifts the plane into the air.

## What a Drag!

When a plane moves through the air, the plane has to overcome drag. Drag is a force similar to friction. Drag slows down objects moving through air. Every part of a plane generates drag, even the engines.

The more streamlined, or aerodynamic, the plane is, the less drag the plane creates. The less drag the plane creates, the faster and more easily the plane can move through the air.

## Overcoming Gravity

Earth’s gravitational force makes it difficult for a plane to fly. You measure the force of gravity (weight) whenever you step on a scale. Gravity is a force that keeps a plane on the ground.
The weight of a plane has to be overcome before it can fly.

## Give It Some Power

Thrust is the force that propels an aircraft through the air. Thrust is used to overcome the plane’s weight and the drag of the air on the plane.

Birds create thrust by flapping their wings. In an aircraft, thrust is generated by the engines. Thrust makes lift possible.