Four Forces of Flight: Lift – Bernoulli’s Principle
Your Activity
Demonstrate Bernoulli’s Principle, one of the ways LIFT is created.
Material
Plain paper
8.5 in by 3.6 in
(8.5 x 11 page cut in thirds)
Bernoulli’s Principle
Bernoulli’s Principle states that as the speed of a fluid (or in this case, air!) increases, the pressure within
that fluid will decrease. On the wing of an airplane, the air over the top surface travels faster so the
pressure will go down. The area under the wing, by comparison, will have higher pressure.
Less pressure down
SPEED
PRESSURE
More pressure up
Activity
1. Hold the paper at the short side at
the corners.
2. Blow gently and evenly across the
top of the paper.
Paper
Blow here!
Hold here!
Paper
What’s going on?
The air over the top of the paper speeds up when you blow over it, so the pressure goes down. The paper
goes up because there is more pressure underneath it.
Four Forces of Flight: Lift – Newton’s Third Law
Your Activity
Demonstrate Newton’s Third Law, one of the ways LIFT is created.
Material
Ruler with a center groove
7 marbles of the same size
Tape
Newton’s Third Law
Newton’s Third Law of Motion states that when two objects interact by exerting force on each other,
these action and reaction forces are equal in magnitude, but opposite in direction. Try this and prove to
yourself that, "Every action has an equal but opposite reaction."
Activity
1.
2.
3.
4.
Tape the ruler to a level table or countertop.
Place five marbles in a row in the center groove of the ruler. Place themtogether, touching each other.
Roll a sixth marble down the groove into the other marbles.
Repeat the experiment, but this time roll two marbles into the row of five.
What’s going on?
The force (action) applied to the first marble is transferred to the following marbles. Those marbles in
turn push (reaction) until the last one rolls down the marble. A moving marble has momentum. When it
runs into the motionless marbles, its momentum gets transferred from one marble to the next. With two
moving marbles, there’s twice as much momentum to transfer. Try to transfer the momentum with three
marbles.
Four Forces of Flight: Lift
LIFT is created by any object moving through the air, but not every object makes enough of it to fly. On an
airplane, the wings and tail are specifically designed to help create lift using airfoils. Those parts of the
plane make the most of lift and help an airplane to fly.
Airfoils
An airfoil is the shape of an airplane wing if you looked at it
from the side. There are many types of airfoils used for different
kinds of aircraft, but the purpose is always to help create lift
using Bernoulli’s Principle and Newton’s Third Law.
The leading edge of an airfoil is at the front of the wing and the
trailing edge is at the back of the wing. If you draw a straight
line between them, you get the chord line.
Angle of Attack
The angle of attack is the angle between the chord line of an
airfoil and the relative wind. Relative wind is not the direction
the wind is blowing, but is created by the airplane as it moves
through the air.
When airplanes are going up, like after takeoff, the angle of
attack is higher to help create more lift. When the airplane goes
down, like for landing, the angle of attack is lower and the wing
creates less lift.
Stall
When the angle of attack is too high the
airflow separates from the top of the
wing. The wing does not stop flying but
without a smooth flow of air the wing will stall
and produce less lift. This is just like when you
stop blowing over the paper in the Bernoulli
experiment.
Lift
Activity Lead Notes
Introduction
Lift is one of the four forces of flight. There are two main ways it is created: Bernoulli’s Principle and
Newton’s Third Law. Most of the information on the info sheet about lift (pg. 3) can be demonstrated in
class using a model airplane before or after the activities.
Preparing Materials
 Bernoulli:
o Cut 8.5 x 11 in paper into thirds (8.5 x 3.6 in) and have one paper for each student.
 Newton:
o 1 ruler per student (or group, if it will be done in teams)
o 1 roll of tape per student (or group, if it will be done in teams)
o 7 marbles per student (or group, if it will be done in teams)
Activity Sheet
Copy the activity sheets and distribute one per student.
Discuss Student Observations
 Bernoulli:
o Ask what students think will happen when they blow on the paper. Is the result what they
expected?
o If it doesn’t seem to be working, remind them the airflow should be smooth and steady, not
a gust of puff.
 Newton:
o Ask what the reaction and reactions are for the activity.
o Alternate/additional activity: In pairs, have students stand and put their hands together,
leaning against each other. In order for both to stand, they have to push the same amount
(equal and opposite) against each other.
o Alternate/additional activities:
http://swift.sonoma.edu/education/newton/newton_3/html/newton3.html
Resources
 Pilot’s Handbook of Aeronautical Knowledge (FAA) (Chapters 2-4):
http://www.faa.gov/library/manuals/aviation/pilot_handbook/
 Beginner’s Guide to Aeronautics (NASA): http://www.grc.nasa.gov/WWW/k12/airplane/index.html