WEIGHT OF A FLYING BIRD             Presenter: Andy Jackson, Harrisonburg City Schools, ajackson@harrisonburg.k12.va.us.

Va. SOL:

PH.1    The student will plan and conduct investigations in which

a)     the components of a system are defined;

b)    instruments are selected and used to extend observations and measurements of mass, volume, temperature, heat exchange, energy transformations, motion, fields, and electric charge;

c)     information is recorded and presented in an organized format;

d)    metric units are used in all measurements and calculations;

e)     the limitations of the experimental apparatus and design are recognized;

f)     the limitations of measured quantities are recognized through the appropriate use of significant figures or error ranges;

PH.5    The student will investigate and understand the interrelationships among mass, distance, force, and time through mathematical and experimental processes. Key concepts include

c)     NewtonŐs laws of motion;

d)    gravitation;

National Standards:

MOTIONS AND FORCES

á       Objects change their motion only when a net force is applied. Laws of motion are used to calculate precisely the effects of forces on the motion of objects. The magnitude of the change in motion can be calculated using the relationship F = ma, which is independent of the nature of the force. Whenever one object exerts force on another, a force equal in magnitude and opposite in direction is exerted on the first object.

á       Gravitation is a universal force that each mass exerts on any other mass. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distance between them.

Topic/Concept

A problem such as this can often be found in texts and challenging logic puzzles: ŇA sealed container contains a live bird. With the bird at rest on the bottom of the container, the system is weighed on an electronic balance. The bird is startled by a loud sound and flies and hovers in the air. How is the reading on the balance affected?Ó

Materials

á      1 kick DisŐ

á      1 sealable container big enough to hold the kick DisŐ

á      1 electronic balance good to the gram.

Safety Considerations

None

Presentation

Students are given the problem to consider. The Kick DisŐ ,the container, and the lid  are all massed separately. The Kick DisŐ is placed in the container w/ o the lid and students are asked to predict mass reading when it is turned on. Reading is made and discussed. The Kick DisŐ is placed in the container, turned on and the lid is pressed on. Students are asked to predict mass reading. Reading is made and discussed.

How the physics is demonstrated

In this demonstration when the Kick DisŐ is on and in the container with out the lid, the mass reading is greater than the sum of the two. When the Kick DisŐ is on and in the container with the lid, the mass reading is the sum of the three. With out the lid, the air pushed down is reflected back upwards and acts as an additional force pressing down on the balance. When the lid is on, this force pushes equally down on the container and up on the lid.

Construction  and Tips Regarding the Demonstration

None  other than a little showmanship prior to and during the demonstration and a good knowledge of NewtonŐs laws for the follow up discussion.

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Sources & References

Kick DisŐ is an estes product and can be found for between \$30 and \$40 through a number of vendors.