15" balloons filled with either H (Hydrogen) or He (Helium) are popped with an 8" "torch" lighter. This is used as an exercise in the scientific method. In science, we make educated guesses based on observations, experiments are performed to test those guesses, the guesses are modified if necessary, and the process continues. Students are shown the balloons, and after noting that whatever is in the balloons must be lighter than air, the students are asked what might be in them. If mentioned, hot air can be discounted since there is not an obvious heat source. Heat must be continuously be added to a hot air balloon to keep it hot. Once choices are narrowed down to H and He, the students are asked to come up with an experiment to tell the difference. This results in the "flame test", since H is very flammable, while He is not.

Laser Light Show

Very few things are cooler than lots of lasers shining through fog and mist to make pretty patterns, especially if lots of students can help out!

Student Wave

Students are asked to make a wave by raising and lowering their hands after their neighbor raises theirs.  This kind of wave is popular at sporting events.  Sound waves are much like this.  Sound will carry energy from one side of a room to another, even though each air molecule only moves back and forth a tiny bit.

Waves on Springs

Long springs are used to show the difference between transverse (up & down) and longitudinal (back & forth) waves.  Sound is a longitudinal wave, and waves on strings are transverse.  Water waves are both transverse and longitudinal.  Wave pulses on the springs will superimpose or add as they pass through each other, but will be otherwise unaffected.  Standing waves, or harmonics, will be shown on the springs, and wavelengths will be discussed.  A wavelength is the distance it takes for the wave to repeat itself.  Long wavelengths mean slow vibrations and low pitches, and short wavelengths mean fast vibrations and high pitches.

Torsion Wave

A giant torsion (twisting) wave machine is used to show that waves move faster if there is a greater force pushing or pulling the stuff back to where it was before the wave passed through.  This is why sound travels through stiff stuff like steel so fast.  Also, the dependence of wave speed on density will be discussed.  Sound travels through water faster than air because it is more dense.

PVC Poppers

Students will use short lengths of PVC pipe to make popping sounds.  Short pipes will make sound of short wavelength and high pitch, while long pipes  will make sound of long wavelength and low pitch.  The students will then play a simple tune with the pipes.

Resonance Boxes

Resonance boxes are short wood boxes with tuning forks mounted on top.  Each box has a natural, or resonance, frequency.  The length of each box is chosen to match the frequency of sound made by the attached tuning fork.  If the tuning fork vibrates, it makes the air inside the box vibrate as well, which makes the sound much louder than a tuning fork by itself would make.  If one resonance box vibrates, it will make a second one vibrate as well through resonance.  The sound from the first box will make the air inside the second box vibrate, which will make the second box and the attached tuning fork vibrate as well.  Sometimes sound will make several things in a room vibrate if the sound frequency matches a resonant frequency of an object.

Hot Crossed Buns

Seventeen students will be directed to sit on whooppie cushions attached to different lengths of PVC tubing to play the tune "Hot Crossed Buns".  The whooppie cushions make sound over a wide range of frequencies.  This is sometimes called "white" noise.  The frequency that matches the resonance frequency of each pipe will be the loudest.

Hoot Tubes

A Bunsen burner is used to make white noise.  Different lengths of tubing are held above the burner.  Sound matching the resonant frequency of the tube will be amplified.  Long tubes will resonate at lower pitch.

Singing Rod

An aluminum rod stroked by fingers covered in resin will "sing" with a longitudinal wave in the metal.  Pinching to rod at different spots will change the wavelength of the sound and the pitch.

Chladni Plates

A metal plate attached to a speaker will vibrate as the speaker makes sound.  Two-dimensional standing waves will be created in the plate.  Waves on a drumhead look like this.  These will be made visible by sprinkling sand on the plate.  Where vibrations are large (antinodes) the sand is flung off, but it will collect where the plate is still (nodes).

Singing Wine Glasses

Wine glasses will be made to vibrate by running a wet finger along the rims.  The pitch of each glass is determined by the amount of water in the glass.  With very little water, almost all of the glass vibrates, and the pitch is low.  With lots of water, much less of the glass vibrates, and the pitch is high.  In general, larger glasses will make lower notes, and smaller glasses will make higher notes.

Break the Wine Glass

Sound inside a sealed box will make a wine glass vibrate at its resonant frequency.  The vibration is "slowed down" with the use of a strobe light.  If we can match the resonant frequency exactly, we should break the glass.  If not, just watching the large vibrations of a big glass is pretty cool.

Beats

If two pure notes are very close together in frequency, they will alternately constructively interfere and destructively interfere.  This makes a "beating" sound.  You hear the average of the two notes, but the volume oscillates, or changes.  Musicians use this to tune their instruments.  The closer two notes are to each other, the slower the beating.  Musicians try to make their notes close enough to each other so that the beats are far enough apart to not be very noticeable.  The resonance boxes show this very well.  A weight moved slightly on one of the tuning forks changes the frequency enough so that beats are heard when both resonance boxes are struck.

Recipe of Sounds

Audioscope, a computer program, is used to analyze sound picked up by a microphone.  Sound vibration will be graphed vs. time.  Pure notes will look like sine waves, while most sounds or notes from instruments will look like several waves added together.  Different instruments and voices make different wave patterns.  In addition to the "pure" sound of a note, each instrument will make many other related sounds, or "harmonics".  The specific set of harmonics and their differing loudness is what gives each instrument its unique tone.  We can easily tell our voices apart and the sound from different instruments apart because of this.  The program can also graph sound intensity (loudness) vs frequency.  Singers use programs like this to help train their voices.

Doppler Nerf Ball

An electric buzzer inside a Nerf ball is used to demonstrate the Doppler effect.  If a sound source is moving towards you, the waves pass you more frequently so you hear a higher pitch.  If a sound source is moving away you, the waves pass you less frequently so you hear a lower pitch.  Police officers use this same effect, but with infrared light, to check the speeds of cars.

Speaker Diffraction

A speaker consists of a drumhead that is driven back and forth.  The sound wave sent forwards is exactly out-of-phase with the sound wave sent backwards.  Sound quickly spreads out, or diffracts.  You can hear someone speaking if they are facing away from you because of this.  The two waves made by a speaker will mostly cancel each other out unless one of these waves is eliminated.  Speakers are put in boxes to eliminate the backwards wave.  A speaker without a box is very faint. 

Flame Tube

The flame tube is a big metal tube with lots of little holes in a row on the top.  The tube is filled with propane, and speakers on both ends are used to set up standing waves inside the tube.  The sound wave can easily be seen by how high the flames shoot up.  Sound is a pressure wave.  Where pressure is highest (antinodes) the flame shoots up high, and where the pressure is lowest (nodes) there is no flame at all.  When music is sent to the speakers this can be a real crowd-pleaser.