Measuring time with a candle

Clock: Any instrument for measuring time intervals.
Dicionários Porto Editora

The clock is one of the earliest inventions of mankind. The first instruments used to measure time were based on solar motion and daylight. These mechanisms had a huge problem; in order to work the sun has to be visible.

Because of this fact it soon becomes obvious that it was necessary to find other methods "to read" the time, methods that were not dependent on weather conditions. Soon people find other mechanisms to track the time such as the hourglass, in which a small amount of sand is placed in a container which has a small hole in the base witch allows the sand to a second container, by changing the amount of sand and / or the hole size is possible to change the velocity of the sand, this mechanism is still used in some community games, it is effective and visually pleasing.

Water clock

Another mechanism is the water clock. This clock like an hourglass consists of two containers, initially empty, the containers and placed one above the other. The top container has a hole in the base; the other one has a scale. We fill up the top container that will "pouring water" to the second container.

Today we use clocks with milimetric precision, and we have atomic clocks that set universal time. The website zenite.nu, states that until 1986 the Greenwich Mean Time or GMT was used as the world standard but was replaced by the Coordinated Universal Time ou UTC, which is based on atomic standards

Sun clock- Lisbon Cathedral walls

UTC is the world standard accepted by "International Bureau of Weights and Measures".
0.00 UTC still means 0.00 in the GMT standard.

Today we are going to build a candle clock.
It's simple to understand and easy to work with.

What we need: 

• 2 candles, similar,
• string,
• black marker,
• 2 candle holders,
• 1 dish,
• a few bolts,



Hourglass

• clock.

How to:

1. Make sure the candles are similar, size and thickness;
2. Place both the candles on the candle holders;
3. Light the first candle;
4. Count 10 min, you can set an alarm;
5. When the alarm goes off make a mark with the pen in the second candle, marking the high of the first candle after 10 min;
6. Repeat the step 4 and until the first candle runs out.
7. At the end you should have a candle like the one in the picture;
8. Tie the bolts to the candle, one in each pen mark;
9. Place the candle+ candle holder in the dish;
10. Light the candle.

Marked Candle

What happened?
Every10 minutes a bolt will fall in the dish, working as an alarm.

Why?
The first candle works like a standard, we used it to know the rate of burning of the second candle, that’s why it's important both candles are similar.
Of course this clock is completely inaccurate, but it’s a good start. We can read in many candle tags its estimated life time, this is always only a reference, in fact a candle duration is related with many factors.
Another thing we must have in mind is that the "marks" on the second candle were made without using a measuring instrument.

If you want to go further:

Industrially marked candle

• Use the ruler to mark 1/2 inch segments on the candle, light it and measure the time it takes to get there. Answer the question: All segments take the same time to burn? Why?
• Get similar candles in different colors. Do they all burn at same rate?
• Get similar candles, all at same color but with different brands. Do they all burn at the same rate?
• Get similar candles, all at same color and brand but with different wax. Do they all burn at the same rate?

Important:

• Use at least 3 candles of each to get more accurate results. You will take the average at the end;
• Change one, and only one variable at time, otherwise you will not be able to get a real cause/effect;
• Take note of all results and observations in your notebook

Warning: The candle is hot, caution! Do not move the candles while the experiment is going. 

References:
http://www.sobre.com.pt; http://www.infopedia.pt; http://www.zenite.nu; Mandell, Muriel, 1998, "Experiências Simples sobre o tempo com materiais Disponíveis" Bertrand Editora

Et voilá!
You will never let the time fly again.

Enjoy!