Dec. 3 – Properties of Waves

Today we played with some more toys that demonstrated waves, including this thing:

This device is called a Bell wave machine an is used to demonstrates how waves work.

Wave Reflection

What happens when a wave hits the end of the medium?  We did it with the Bell wave machine pictured above and with this online simulation:

• http://phet.colorado.edu/en/simulation/wave-on-a-string

We can summarize the results as follows:

• When a wave hits the end of the medium, it is reflected.
• If the boundary is rigid (fixed) the reflected wave is inverted.
• If the boundary is loose the reflected wave is upright (on the same side of the equilibrium).

More Definition

-  Oscillation: a motion that repeats itself

-  Cycle: the point where an oscillation begins to where it repeats (same as one wavelength)

-  Period: the time it takes to complete one cycle, T (measured in seconds)

     The period of a wave is related to its frequency.

     T = 1 / f        or     f = 1 / T

Speed of a Wave

From kinematics v = ∆d / ∆t

For a wave, ∆d can be the wavelength (lambda).  ∆t can be one period.

Therefore:   v = 入 / T

or in terms of frequency

                  v = 入 f

This is called the Universal Wave Equation!

- works for ANY wave in any medium

Handout

• Universal Wave Equation Worksheet

More demonstrations

We also played with this tone generator to see if we can all hear the same sounds.

• Online Tone Generator

It turned out I couldn't hear any sounds with a frequency over 15 000 Hz, but you guys can!