**Apparatus Competition**

**2006 AAPT Summer Meeting**

**Syracuse, NY **

** **

**Surface Gravity Waves: Resonance in a Fish Tank**

** **

**John J. Lynch**

Department
of Physics

Wheeling
Jesuit University

316
Washington Ave.

Wheeling,
WV 26003

304-243-2287

jlynch
ÔatÕ wju ÔdotÕ edu

** **

**Abstract:**

This
apparatus is used to study wave motion using a 10-gallon glass aquarium. It is
an alternative to vibrating strings and resonance tubes. The equipment needed
is inexpensive and the resulting waves are much slower than those produced by
string vibrators and tuning forks. Times can be measured with a stopwatch. In
addition, students can study projectile motion with the squirt gun.

**Construction of Apparatus:**

10-gal Aquarium Tank

Stopwatch

Plastic ruler

Meter Stick

2 Styrofoam strips

Squirt gun

Water

**Use of Apparatus:**

(1)
Fill the tank with water to the desired depth, *D*.

(2) Measure
the inside length of the tank, *L*.

(3)
Excite the fundamental resonant mode (*n*=1).
The antinodes will be at the edges of the tank. Place the styrofoam strips at
these edges and begin to move them up and down and out of phase. Let the water
establish the tempo.

(4)
Once a clear standing wave is visible, remove the strips and use the stopwatch
to measure 20*T*--the time for
twenty oscillations.

(5)
Obtain the wavelength *λ _{n}* from

the condition for resonance.

(6)
Calculate the wave speed using the wavelength and the period.

(7)
Calculate the wave speed using the dispersion relation for surface gravity
waves.

(8)
Compare the two numbers from steps (5) and (6).

(9)
Excite the next fundamental resonant mode (*n*=*n*+1).
Place the Styrofoam strips where antinodes are expected to be and move them up
and down in the water. Let the water establish the tempo. Return to step (3).