the world in a different light
A video tutorial on the use of the Addestation datalogger with its motion sensor to measure the displacement of a bouncing ball and to observe the velocity and acceleration using its differentiation function.
This video tutorial is a guide for next week’s practical for CG18/12.
Audacity is a free audio recording and editing software downloadable from http://audacity.sourceforge.net. It is cross-platform meaning you can run it on PC or Mac.
Once you have the software installed, you can try out some of its simpler functions, such as recording and playing back. You can also generate tones of known frequencies, which will be useful for experiments such as using stationary waves to determine the speed of sound in air.
Frequency and pitch
The first activity serves as an introduction to the software and can be easily carried out. All you need is a computer with Audacity installed and a microphone connected to it. Tuning forks of different frequencies will be best for this activity because of the simple and pure waveforms generated. A regular wave pattern can also be recorded with the help of a musical instrument such as a guitar or by singing a note.
To make a sound with the tuning fork, strike it against something hard such as the heel of your hand. The two prongs of the fork, known as “tines,” will then vibrate with a fixed frequency, thus generating a waveform with a displacement that is almost sinusoidal. Place this tuning fork next to the microphone and you should see a densely packed waveform like the following:
Zoom into the peaks recorded by clicking on the peaks of interest and pressing Ctrl 1 for Windows or Command 1 for Mac. You should observe a repeated pattern in the waveform.
By reading off the time difference on the horizontal axis between two peaks, you can measure the period of the wave. Using $$f=\frac{1}{T}$$ where f is the frequency of the wave, and T is the period, you can verify the frequency measured with the known value of the tuning fork’s frequency.
In the above graph, the period is 2.8190-2.8155 = 0.0035s. The frequency of the tuning fork used is given by $$f=\frac{1}{T}=\frac{1}{0.0035}= 286 \text{ Hz}$$ which is roughly that of a D note.
image taken from http://courseweb.stthomas.edu/apthomas/SquishyCircuits/howTo.htm
I came across this Ted video on Squishy Circuits, presented by AnnMarie Thomas from the University of St Thomas and found it to be a suitable activity for kids. I shall attempt to make some when I am free with instructions from the following site:
http://courseweb.stthomas.edu/apthomas/SquishyCircuits/index.htm
Be sure to watch this page for photos and videos!
As I was contemplating the potential of combining conductive and insulating dough to make fun toys with the help of electric motors and the learning that can come from it. Apart from the obvious learning related to electrical resistance and current, we can even learn about flotation and fluid dynamics by building floating boats of different hull shapes.
With the help of a simple manual vacuum pump that is used to keep food fresh, we can demonstrate the effect of a reduced pressure on the boiling point of water. This leads students to a discussion on what it takes to boil a liquid and a deeper understanding of the kinetic model of matter.
Materials
Procedure
Explanation
When water boils, latent heat is needed to overcome the intermolecular forces of attraction as well as to overcome atmospheric pressure. Atmospheric air molecules would prevent a significant portion of the energetic water molecules from escaping as they will collide with one another, and cause them to return beneath the liquid surface.
Removal of part of the air molecules within the jar lowers the boiling point of water because less energy is needed for molecules to escape the liquid surface.
In a previous demonstration, we put a boiled egg into a flask with a mouth narrower than the egg. The challenge is now to remove the egg from the flask without breaking it.
Materials
Procedure
Explanation
The flame heats up the air and the water in the flask. The heated air expands while some of the water vapourizes. With the increase in amount of gas and temperature, the pressure within the flask increases.