# Forces in flight (M)

#### Do you remember what the term Aerodynamics means?

Aerodynamics studies how air moves and how it reacts to objects moving through it.  Gases expand and contract to fill the area available to them.  That means that as an object moves through air, air moves and flows around the object.  A sheet of paper, flat and not crumpled up, will move through the air very differently than the same sheet of paper crumpled into a ball.  This is important to study and understand when designing many kinds of vehicles.  Let’s look at some of the forces they have to understand.

This diagram shows the four main forces we will look at and the direction those forces push or pull on the plane.

Thrust is the forward pushing force.  When you are running, that force is generated by your legs pushing you forward.  When you throw a paper airplane, your arm pushes the plane to propel it forward.  Engines provide the forward thrust for airplanes.

Lift is the force that pushes the plane upward off the ground.  You can look at this picture to get an idea of how air flows over the wing.  The air moving over the wing moves faster and has lower pressure.  The air under the wing moves slower and has higher pressure.  These pressure differences cause the lift force which pulls the plane up off the ground.

When you jump as high as you can straight up into the air, what makes you come back down to the ground?  Gravity is the force that pulls down on you and everything else, pulling toward the earth.  Plane design has to calculate the force of gravity pulling down on plane.

Drag is the force pulling back and slowing down the plane.  Newton’s Laws of Motion explain that for every action, there is an equal and opposite reaction.  As the air hits the plane, the plane is pushed back.  Drag is caused by air flowing around the plane, pushing on the wings and running into different parts of the plane.

Designers and engineers have to have a thorough understanding of all these forces and how they work together to design planes that will fly successfully.  There must be enough thrust to oppose the drag pulling on the plane.  The lift created by the airflow over the wings must be stronger than the pull of gravity on the plane.  When they can create a design that correctly balances all these forces, they can achieve flight!

Pilots have to understand how all these forces work together, too.  As a pilot is controlling a plane, understanding lift and thrust can help make decisions if something goes wrong during the flight.  Stunt pilots take the time to understand how these forces work together and how to manipulate the plane to plan stunts and tricks.  Have you ever watched a stunt pilot perform acrobatics with a plane?  You can watch this video to see some of the amazing tricks they can do when they have a good working knowledge of these forces!