What makes something fly?

The Four Forces of Flight

There are four forces that act upon an object to make it fly:

• Lift = upward pull
• Weight = downward force of gravity
• Drag = force opposite to the direction of motion (friction)
• Thrust = force that moves an object forward

When the forces of flight are balanced, an object can fly in a level direction.  An object can go up (take-off!) if the forces of lift and thrust are more than weight and drag .  An object can go down (land!) if the forces of weight and drag are greater than lift and thrust.

Take Off = Lift + Thrust > Weight + Drag

Landing = Lift + Thrust < Weight + Drag

How do objects DEFY gravity?
In other words, how can we create the lift needed to overcome weight (the force of gravity)?  
Lift can overcome weight in two ways:

1) By creating differences in air pressure.
2) By pushing air downward.

But what does this even mean?!?!?!  There there.  I'll explain.

1) Create lift by creating differences in air pressure

• The shape of a wing is called airfoil.  The airfoil is what enables a plane to create lift.
• The curved shape of a wing (airfoil) makes air above the wing move faster than the air below the wing. 
• Fast moving air has lower pressure than slow moving air, so the higher pressure air pushes the plane upward toward the low pressure area, generating lift.  This is known as Bernoulli's Principle.

Bernoulli's Principle: As the speed of a moving gas or liquid increases, the pressure within the gas or liquid decreases

Daniel Bernoulli was the Swiss mathematician who first described the phenomenon that as the movement of a fluid increases, the pressure decreases.

2) Create lift by pushing air downward

• A wing is shaped to force air downward, which causes an equal and opposite reaction from the air, forcing the wing upward.  This is an example of Newton's 3rd Law of Motion.
  
• When a bird flaps its wings, it is pushing air downward to pull itself upward.

Newton's 3rd Law of Motion: For every action, there is an equal and opposite reaction.

Isaac Newton was one of the greatest scientists and mathematicians who ever lived. He defined the "Laws of Motion" that describe the relationship between a body and the forces acting upon it.

So now we have Lift.  Where do we get Thrust?
That's a much easier explanation.  We get thrust from engines (like a car), propellers, and rockets!

Still confused?  Watch the Bill Nye + BrainPop videos on flight (videos + links below)!

BrainPop: Flight
Username - ms881
Password - ms88rocks

Assignment
Answer the questions below in complete sentences, using the blog post, videos, and class notes to help you.  WRITE the question and answer.
Due: Friday, June 6, 2014

1.  What are the four forces of flight?
2.  How does a plane balance the forces of flight in order to land safely? (hint: some forces must overcome others)
3.  What is an airfoil?
4.  Sketch an airfoil.
5.  What is Bernoulli's principle? 
6.  How does Bernoulli's principle relate to flight?
7.  What is another example of Bernoulli's principle in the real world?  (hint: there is a poster in Ms. Shon's classroom with examples)
8.  What is Newton's 3rd Law?
9.  How does Newton's 3rd Law of motion relate to flight?
10. What is another example of Newton's 3rd Law of motion in the real world?