Thursday 19 September 2013

Why Does The Candle Flame Point Upwards?

Today is the fifteenth day of the eighth lunar month and many are celebrating the Mid-Autumn Festival. This festival is meant to celebrate friendship, fertility and togetherness and there are a number of traditions associated with celebrating this festival, one of them being the iconic paper lanterns. Lanterns in general are portable lighting devices that comes in various shapes, sizes, and materials with a light source inside usually candles or an electricity-powered bulb. For the Mid-Autumn Festival, candle-lighted lanterns are typically used and which gives a beautiful gentle glow that flickers with the wind.
What is a candle though and how does it provide light? A candle consists of wax and a wick. Most candles are made from paraffin wax, i.e. they are hydrocarbons and are composed of hydrogen (H) and carbon (C) atoms. Just like other hydrocarbons such as the fuel we pump our cars with, wax is the source of energy for the candle. When we light a candle, the heat of the flame melts the wax near the wick, feeding the fire with something to burn. What happens is that the heat of the flame vaporizes the liquid wax and starts to break down the hydrocarbons into molecules of hydrogen and carbon. These vaporized molecules are drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapor (H2O) and carbon dioxide (CO2).
Lanterns lit by candles are used both indoors and outdoors. The candle is placed inside colourful and beautiful paper lanterns that fills the night with colours. However, as most lanterns are made of paper and we all know that paper burns quite easily, why is it that the paper lanterns do not get consumed by the flames from the candle within? Of course if the paper comes in contact with the flame, it will burn but generally, the flame of the candle only point upwards and do not move too far to the side therefore keeping the paper lanterns safe from being burned up. Do you know why the flame point only upwards?
When a candle burns, the flame heats the nearby air and starts to rise. As this warm air moves up, cooler air and oxygen rush in at the bottom of the flame to replace it. When that cooler air is heated, it too rises up and is replaced by cooler air again. This creates a continual cycle of upward moving air around the flame, which gives the flame a teardrop shape. Basically the continuous movement of hot air going up displaces cooler air down to the side which then gets heated up again and move upwards causing the distinctive shape of the flame and which is why it points only upwards.

Something to think about though, if you light a candle in space, how will the flame look like? Do you think it will be the same shape? Does gravity play a role? Let us know if you have the answer by leaving a comment!

Posted by Ayu
Learning Specialist, Petrosains

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