Sine Wave Basics

Consider the second hand on an "old-fashioned" round clock face: The hand makes an angle relative to a horizontal line drawn through the shaft from 9 to 3. The sine of that angle is proportional to the height of the tip of the hand above this reference line. (Heights are negative if the tip is below this.) Start with the hand at 9, and measure the height as it passes each numeral on the face:

This is one cycle of a classic sine wave.

The amplitude of the clock sinusoidal wave is the length of the hand, which is the maximum height above or below the horizontal reference line.

The frequency of the wave is the number of cycles per unit time. On a clock, the second hand completes one cycle per minute. Although those who deal with rotating machinery use Cycles Per Minute (CPM), other users commonly refer to frequency in cycles per second, so we would say that the second hand completes 1/60 cycle per second. One cycle per second is called one Hertz, abbreviated Hz and pronounced "Hurts" like the car rental agency (although medical doctors sometimes say "Hairtz").

We apply standard scientific prefixes to this, so 1000 Hertz is 1 kiloHertz (kHz) and 1/1000 Hz is 1 milliHertz (mHz). Our second hand thus has a frequency of 1/60 Hz or 0.0166667 Hz or 16.6667 mHz. Note the small 'm' in 'mHz'. A large 'MHz' is used to refer to 1 million Hertz or MegaHertz. Small letters refer to prefixes less than one, capitals to those more than one. The exception to this is small 'k' for kilo... a tribute to the group wisdom of standards committees. Daqarta allows you to enter either 'K' or 'k', but always shows this as 'k'.

See also Sine Wave Phase, Magnitude via Vector Sum, Making Waves via Sine Wave Synthesis