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Strobe Labs
The labs and activities listed below were written for a 2nd-year
high-school physics class. They could also be
used in introductory college physics courses. The labs all use
high-speed images. In some cases, a series of high-speed photographs
has been assembled into a video clip that can be played back to give
an effect similar to a high-speed movie. (These are termed photo
sequences below.) A video analysis program such as
Tracker can then be used to extract data from the clip.
The level of mathematics required is indicated in parentheses.
The
Bouncing Ball -- A Challenge -- A photo sequence of a ball
bouncing across a table is shown without providing any information
about the distance scale of the images. The problem is to
determine the diameter of the ball indirectly, using the physics of
projectile motion and the fact that the photos were taken on the
surface of this planet. (Level:
Pre-Calculus)
Average
Force of Impact in a Tennis Ball Collision -- A photo
sequence shows a tennis ball colliding with a wall.
Measurements are made of the velocity of the ball before and after
the collision and of the duration of the impact. The average
force of impact can then be calculated. (Level:
Algebra)
Deceleration
of a High-Speed Projectile in Water -- A photo sequence
shows the path of a BB projected downward into a tank of water at
two-thirds the speed of sound. The displacement of the BB is
measured as a function of time and compared to a theoretical
equation that the student derives. (Level:
Calculus)
Trapped! Analysis
of a Real Collision -- The collision of a BB with an elastic
strip is investigated through the use of multiple-image
photographs. The force acting on the BB as a function of time
can be found, yielding some interesting results. For more
information, see the
Inertia!
project. (Level: Pre-Calculus)
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