Science

Unit 1 - Flight

The Four Forces

Four Forces Affect Things That Fly

1. Weight is the force of gravity. It acts in a downward direction—toward the center of the Earth.

2. Lift is the force that acts at a right angle to the direction of motion through the air. Lift is created by differences in air pressure.

3. Thrust is the force that propels a flying machine in the direction of motion. Engines produce thrust.

4. Drag is the force that acts opposite to the direction of motion. Drag is caused by friction and differences in air pressure.

All Four Forces Act on an Airplane

When an airplane is flying straight and level at a constant speed, the lift it produces balances its weight, and the thrust it produces balances its drag. However, this balance of forces changes as the airplane rises and descends, as it speeds up and slows down, and as it turns. 

Only Two Forces Affect a Spacecraft in Space

A spacecraft has weight, even in orbit, and uses thrust to reach space and to maneuver. But lift and drag—both created by movement through air—are absent in the near vacuum of space.

Characteristics of Air

·         The gasses that make up air are colourless, ordourless and tasteless.

·         Air has no shape of its own but takes the shape of the container it fills (e.g. the plastic bag).

·         Although air is invisible – it is real and takes up space.

·         Air has weight – gravity gives air weight.  At sea level, 30 000mL of air weighs 3.7grams.

·         Anything that has weight, will push or press against things – air therefore has pressure.

·         Air presses in all directions, downward, upward, and sideways. Air presses just as hard up and down as it does sideways.

·         Moving air exerts pressure – increasing the pressure as it moves (the harder the wind blows, the greater the pressure it will have).

Bill Nye Video- Flight