## TIME KEEPING… LEAP SECOND???

what’s a leap second?

The time it takes for earth to rotate around the sun actually isn’t consistent, it differs few fractions of seconds. This is the reason why we add leap seconds once in a while. Recently on june 30th 2015 we added a new second.

Time keeping!!

So, we created the time. We can’t actually sense time with our senses. Learn more about the nature of time right here Nature of time. So, Before we talk about time keeping which is so long indeed, let’s quickly see

Since ages we humans are trying to make time more and more accurate. So let’s get to the history, in 3500BCE Egyptians started measuring time using sun. By placing a tall stick or something, which casts shadow in a particular place according to the suns position. But this isn’t accurate because this doesn’t work on a cloudy day and this changes the durations according to the season change.

So, to overcome this problem “Mechanical clocks” were built. As the time is calculated based on a relative change, these clocks also work on the same principle “Measuring time using a repeated process”. The first in that kind were Water clocks, which measure time according to the volume of water dropped at a constant rate in a marked container. And these mechanical clocks became sophisticated and we started using notched wheels for the constant movement but there was a problem in regulating the speed of the wheel. Now here come the concept of Pendulum. Galileo in 1600 studied the motion of a pendulum, which states that no matter what the mass of the pendulum is, it makes back and forth motion rate constant depending on the length of the pendulum. And this concept was used to build a pendulum clock.

These pendulum clocks were great, but these clocks were a problem to the sailors who often were on the moving ships. To solve this problem John Harrison invented a pocket clock which works on a spring mechanism.

After a long gap, in 1960 Quartz clocks were invented. Quartz crystal is a Peizo electric material, which gives out electricity by applying pressure and vice versa. Learn more about working of Quartz watches on my previous post How a Quartz watch works?. It changes only 15 seconds per month which is pretty much accurate than the precious clocks.

But we need still more accuracy, we depend on time more and more these days, for example the stock market.

For still more accuracy we invented Atomic clocks. Previously a second =1/32,000,000 of an year according to the rotation of the Earth. Scientists felt that, even this is not accurate, the rotation of the earth in its orbit also varies every year due to many factors like moon.

So, to get the most accurate time, the second was defined based on the INTRINSIC property of CESIUM. In these atomic clocks the Cesium is used to tune the waves to a specific frequency. Which has 9,192,631,770 Hz frequency when ever the clock hits that number it counts one SECOND..

For still more accuracy scientists invented Optical clocks which will not show even a second difference for 13 billion years!!!

So let me know your feed back…

## “QUARTZ WATCH” How does it work?

The Quartz watches are the most extensively used watches because of their most accurate Timekeeping.

The watch uses a tiny piece of quartz crystal which is the main ingredient of sand “silicon-dioxide” , Quartz crystals are piezoelectric, which means that they generate an electrical charge when mechanical pressure is applied to them. They also vibrate if an electrical charge is applied to them. The frequency of this vibration is a function of the cut and shape of the crystal. Quartz crystals can be cut at a consistent size and shape to vibrate at thousands of times per second(around 32,000Hz), making them extremely stable resonators for keeping very accurate time.

If you have read my previous posts, you might be knowing what exactly “Piezoelectricity” is. If you missed it here’s the link Piezoelectricity.

That quartz crystal serves as the oscillator. The battery sends electricity to the quartz crystal through an electronic circuit.  The circuit counts the vibrations and generates regular electric pulses of one per second. Now the motor comes into picture, the electric pulses when reaches the motor, the motor turns the seconds hand and the clock works,

Higher accuracy devices generally use a material with even higher frequencies (again the frequency must be as stable as possible). Atomic clocks count the oscillations between the nucleus and the electrons in an atom (typically cesium) which oscillate at around 9 billion Hz.