SCIENCE CONCEPT:
- Most of us are familiar with the boomerang, the
wonderful stick that returns when you throw it. To understand why a
boomerang returns, we must look at the shape of the boomerang, the
aerodynamics and physics.
STUDENT OBJECTIVE:
- The student will learn how and why a boomerang
returns and how to throw it so that it will return.
OVERVIEW:
- The student will be exposed to the aerodynamic and physics
that are involved in why a boomerang returns when thrown properly. The
student will also learn how to correctly throw the boomerang so that it
will return when thrown.
TEACHER TEXT:
- The boomerang consists of a leading wing and a trailing
wing connected at the elbow. Each wing has the typical cross section of
an airfoil. Therefore, each wing has a leading and trailing edge
arranged so as the leading edge strikes the air first as the boomerang
rotates. The typical angle between the wings is 105 degrees to 110
degrees.
When a boomerang is tossed in the correct manner, the
wings rotate through the air and react to the aerodynamic and gyroscopic
forces. These forces cause the boomerang to circle around and lay down
as it returns, until it descends in a horizontal hover. During the
flight of the boomerang, the following principles come into play:
Bernoulli's relation, gyroscopic stability, gyroscopic precession, and
Newton's laws of motion.
AS the boomerang flies through the air, each wing
produces lift. Once again, Bernoulli's principle is used to explain how
the lift is formed. The air moves faster over the upper surface than the
air moving over the lower surface. This means that a pressure
differential exists between the lower and upper surface which translates
into lift.
A boomerang is thrown with a spin in a similar manner as
the discus and frisbee. This spin has two effects on the boomerang as it
travels through the air. The first is a stabilizing force known as
gyroscopic stability. The second effect of the spin results in the
curved flight of the boomerang. The turning force imposed on the
boomerang comes from the unequal air speed of the spinning wings. If we
start with a stationary, spinning boomerang, both wings would produce the
same amount of lift. Now give that same spinning boomerang a forward
velocity and the speed of the air traveling over the wings differs.
Thus, the forward moving wing experiences more lift than the retreating
wing. The net result is a force which turns the boomerang. Due to a
phenomenon known as gyroscopic precession; this force is felt 90 degrees
from where it was applied. Gyroscopic precession is the principle
governing the no hands bicycle turn.
Unlike the no hands turn, the boomerang experiences a
continuous turn as the force is applied for the duration of the flight.
The boomerang is thrown with a slight tilt from vertical. This causes
the boomerang to also lay down as it turns. Thus the boomerang returns
to the thrower in a horizontal hover.
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PREPARATION TIME:
- 15 minutes.
LESSON TIME:
- 45 - 65 minutes.
TEACHER PREP:
- Gather materials
WORDS TO KNOW:
- leading wing
- trailing wing
- rotation
- aerodynamic forces
- gyroscopic stability
- gyroscopic precession
- Bernoulli's relation
- Newton's laws of motion
- vertical throw
- horizontal throw
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