Physical Science Demonstrations
Carl Wozniak
Northern Michigan University
Discrepant Event 1: Spinning cylinders
The spinning cylinder is a piece of ¾ inch PVC pipe cut to a length of about three
times its diameter. Using permanent markers, draw an X in one color and an O in
another color at opposite ends of the cylinder as per the illustration.
Make the X and O a bit bigger than shown. To operate the
device, place your finger on the "X," push your finger down as you pull it toward
you. This will make it spin and rotate at the same time. The question you need to
ask of your students beforehand is “What will you see as you look down on the
spinning cylinder?” Typical responses include: a blur, a merging of the colors, or
the X inside the O. In reality, the cylinder will spin and rotate making a blurred
circle in which three X's can be seen.
Why this happens
When you launch the rod it spins about its long axis and rotates about a line
perpendicular to this axis. As it rotates about its center, the rod forms a blurry
circle on the table top. As the rod spins, the top of one end moves in the same
direction as the end is rotating while the top of the other end moves opposite the
rotation.
The arrows on the cylinder show how it moves: the entire top is
moving down.
The arrows off of the cylinder show how it rotates.On the right end the two
motions cancel, and the top center is visually slowed. On the left end, the
motions are additive, passing out of our vision faster.
Thus only the markings on one end are visible.
Since we see 3 markings around the blurred circle we know that the cylinder is
making 3 spins for every rotation. Cylinders that are cut so that there length is
four diameters have a stable square with 4 markings, those cut to 2 diameters
create a stable pattern of 2 marks.
Discrepant Event 2: The multicollision accelerator
Force = Mass X Acceleration
A rubber ball is attached to a stick. Two additional
balls with holes through them are also permanently attached to the stick, but
have a limited ability to move. A fourth ball is placed over the other three, and
is able to move freely off the stick. Each ball has approximately half the mass
of the ball beneath it.
 The system is dropped from a low height resulting in a large movement of
the smallest ball.
 When the stick/ball combination is dropped on the bottom ball, force is
translated from one ball to the other. Since the force is constant, as the
mass is reduced from ball to ball the acceleration increases. A small drop
of the system results in a large displacement of the last ball.
 This same phenomenon can be observed with a basketball and tennis
ball. Hold the tennis ball directly above and in contact with the basketball
and drop them from shoulder height. When they contact the floor the
tennis ball will go flying.
Energy balls and circuits
Energy balls are ping pong ball-sized plastic balls with
two metal contacts. When both contacts are touched in a completed circuit the
balls light up and make noise. They are great for demonstrating series and
parallel circuits, and will easily work with a group of 30 students.
Discrepant Event 3: Bernoulli effect with ping pong balls
This uses real ping pong balls.
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Bernoulli’s law states that for horizontal fluid flow, an increase in the
velocity of flow will result in a decrease in the static pressure.
Suspend two ping pong balls connected by a string approximately six
inches apart
With a sharp breath, blow between the balls
Most students conjecture that the balls should be pushed apart by the
blast of air between them. In reality, the balls come together as the
pressure between them is reduced below the pressure surrounding them.
Color light addition with colored LEDs
Colored light is additive. Green and red make yellow. Red and blue make
magenta. Blue and green make cyan. Green, red, and blue light together makes
white light. Simple LED devices can demonstrate the color combinations.
Sound amplification with thunder box
Sound is caused by waves displacing a medium. To hear sounds, our ears pick
up a small vibration with the tympanic membrane which is converted to a larger
vibration by a series of levers (ear bones) and a fluid filled coiled tube (cochlea).
The thunder box amplifies the vibrations of a coiled wire through a fiberglass
membrane and large tube to create a realistic representation of distant rolling
and crashing thunder.
Transverse and longitudinal waves with singing rod
An aluminum rod can be made to vibrate transversely
by rubbing it longitudinally. Fingers stutter along the rod, creating oscillations at
the free ends that develop into a piercing noise. Holding the bar at the half and ¼
points creates different sounds.
Vacuum physics
 Ringing bell
o A ringing bell in a vacuum chamber makes no sound as the air is
removed. Sound must travel through a medium.
 Marshmallows
o Marshmallows are sugar cells surrounding air pockets. In a vacuum
chamber the marshmallow expands until the cells rupture and then
the marshmallow’s elasticity returns it to its original size. This
shrinking seals the holes. When the air returns to the container the
marshmallow collapses.
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Feather and penny drop
o A classic of Gallilean theory is the demonstration of the fall of a
feather and a penny due to the force of gravity. In air, air resistance
slows the feather. In a vacuum, they fall at the same rate.
Gyroscopic action with vortex flyer
Spinning an object gives it stability. The vortex flyer is a cylindrical paper
airplane. Shooting the plane from its launcher without rotation results in an erratic
flight path. Shooting with rotation creates an even, long-distance flight.
Airzooka and fog machine
The airzooka launches rings of air up to 20
feet. The rings can be observed by filling the gun with smoke prior to shooting.
The device is great for demonstrating force and motion, and the fact that air is
composed of “stuff.”
Sources:
Steve Spangler Science: http://www.stevespanglerscience.com
American Science and Surplus: http://www.sciplus.com
InnovaToys: http://www.innovatoys.com/
Science Toys: http://scitoys.com/
Edmund Scientific: http://scientificsonline.com/
Educational Innovations: http://www.teachersource.com