Rods attached to metal spine; transverse wave generator shows the reflection of waves free, fixed, terminated and transition boundaries.
What it shows
Mechanical demonstration of transverse standing or traveling waves using the Shive wave machine.
How it works
The Shive wave machine consists of a series of horizontal metal rods 1.25 cm apart coupled by a torsion wire. A pulse can be sent down the machine by displacing the end rods (when doing this by hand, pull down on more than one rod as the connections are delicate and do break). The far end can be lamped for rigid termination to show reflections, or damped using a pair of dashpots which absorbs the energy and prevents reflections. There are three attaching units, one having 46cm long rods, one with 23cm rods, and an 'impedance matching' section with intermediate lengths. The 23cm rod section has a wave propagation velocity three times that of the 46cm section.
Setting it up
The wave machine is mounted on its own foldable base. The tips of the rods on our machine are coated with fluorescent paint; with the hall lights down and a 4ft black light placed in front and below the rod level, only the tips can are visible, making the wave motion beautifully clear. The dashpots 1 are attached to the last rod in the line (how far down the length of the rod for best damping takes a bit of experimenting). The driver attaches by an alligator clip to a taped loop over the first rod.
Comments
The Shive wave machine was developed at Bell Labs by John Shive. His handbook (see Reference) is a good accompaniment. Our Shive wave machine is from Pasco Scientific (SE-9600); Cenco have a similar machine (32694). The 46cm section is usually used alone.
The wave machine can be driven with a 12V DC motor 2 controlled by a multi-turn pot, with the driving cam attaching by alligator clip to a taped loop over the first rod.
Reference
J. N. Shive: Similarities in wave behavior Bell Telephone Laboratories (1973)
1 Adjustable air dashpot by Airpot Corp. Norwalk Conn.
2 12V DC motor CYQM42810-31-5 Barber Colman, Rockford, Ill.
