In this class we talked about sending waves down a string (or a slinky) and setting up different standing waves on strings and in tubes.  I used the String App by Ricardo Varjao on my ipad to demonstrate, though the class had down it the week before with a long coiled spring I have for that purpose.  This app will generate a pulse  or a wave for you, or you can wiggle the ‘string’ yourself with your finger.

speed of soundFor a lab the students used tuning forks and plastic tubes to measure the speed of sound in air.   The open tube was held in a graduated cylinder full of water, effectively making one end of the tube closed, and one opened.  The students struck a tuning fork and held it over the open end, moving the tube up and down in the graduated cylinder, increasing or decreasing the length of the tube.  When you get the length of the tube to match a quarter of the wavelength of the sound wave from the tuning fork, you get resonance and the sound becomes considerably louder.  Once the students found the right length for the tube they recorded it in their lab books and could calculate the speed of the sound wave, v = wavelength x frequency (read off the tuning fork).  This was done for a number of different frequencies and then they calculated the average.  Both groups found the speed of sound in air to be close to 330 m/s, very close to actual speed of sound of 340 m/s.

We also made straw wave models like the ones in these videos using coffee stirrers since I had them on hand.

 

Advertisements