This week, we’re taking a look At the ever-popular demonstration G3-28: Suspended Slinky®. This handy device lets us demonstrate both transverse and longitudinal waves in the classroom. You can see it in action in this new video with physics student Jeffrey Wack.
As Jeffrey shows us, there are two directions that matter when characterizing a wave: the direction of propagation, where the wave as a whole is going; and the direction of displacement, the motion of the individual elements that make up a wave. In a longitudinal wave, these are parallel – the individual particles of air in a sound wave move back and forth in the direction of travel of the sound, or the individual loops of wire in a spring move back and forth along the length of the spring. In a transverse wave, by contrast, they are perpendicular – the electric and magnetic fields in a radio wave oscillating perpendicular to the direction of propagation, or the loops of a spring swinging side to side as a transverse wave moves down the length of the spring.
There are many kinds of waves in the world, some transverse and some longitudinal, and some that combine characteristics of both! These animations by Dan Russell of Penn State illustrate some examples of this, such as waves in water where the individual water molecules are actually moving in a circle as the wave propagates through.
You can experiment with comparing longitudinal and transverse waves at home with this simulator from Tom Walsh at oPhysics. Try setting different amplitudes and frequencies, and see what changes in each wave as you do so.