Total Defence Day is marked annually on February 15 in Singapore to commemorate the anniversary of the surrender of the British to the Japanese on February 15, 1942. It serves as a reminder that Singapore is defensible and is worth defending, and only Singaporeans would have the will to defend Singapore.
At 12:05 pm, the Singapore Civil Defence Force (SCDF) will sound the 1 minute long Important Message Signal through the island-wide Public Warning System (PWS) sirens. The 10 local radio station will then explain the appropriate measures to be taken for the three different types of PWS signals.
Besides the ‘Important Message’ signal (characterised by pulsating blasts), the two other signals are the ‘Alarm’ and the ‘All Clear’ signals, which are characterised by wailing and continuous blasts respectively. The sounding is part of SCDF’s continuous efforts to familiarise the public with the three PWS signals and raise awareness on how they should react upon hearing each signal.
From this exercise, we can see that sound is all around us and it plays a central part in our daily life. Besides using sound to communicate important information, sound also provides us with music which can have a powerful emotional effect on people. So have you wondered how is sound produced? Why are there so many different type of sound?
Sound is produced when an object moves or vibrates causing the particles around it to vibrate creating a series of compression and rarefaction. Our ears vibrate in a similar way to the original source of the vibration, allowing us to hear many different sounds.
Music can be generated when we vary the frequency, amplitude and harmonic constitution, or waveform of the sound wave which will in turn affect the pitch, loudness(or intensity) and quality(or timbre) of the sound respectively.
Here are some interesting sound experiments that you can try at home.
