Tanah Liat & Kesan Penyejukannya

Nampak kotor serta menggelikan. Tetapi tidak untuk pesawah yang sentiasa bergelumang dengan tanah liat demi untuk mencari rezeki. Sungguhpun begitu, tahukah anda ia mempunyai banyak kelebihan luar biasa seperti ia mampu memberi kesan penyejukan?Apakah ciri-ciri yang ada pada tanah liat sehingga ia dikatakan sangat unik? Apakah pula proses sains yang terlibat?

Rumah yang beratapkan tanah liat

Tanah liat adalah jenis tanah yang memiliki struktur  liang-liang halus. Pada atap rumah yang diperbuat daripada tanah liat seperti dalam gambar di atas, liang-liang halus berfungsi untuk menyerap haba cahaya matahari  dan sekaligus, menghalang haba tersebut memasuki ruang dalam rumah. Ini akan menyebabkan ruang dalam rumah menjadi kurang panas pada waktu siang berbanding rumah yang mempunyai atap yang diperbuat daripada bahan lain.

Kepingan-kepingan atap diperbuat daripada tanah liat 

Manakala air yang disimpan di dalam labu sayung yang diperbuat daripada tanah liat akan menjadi lebih sejuk daripada suhu di sekeliling disebabkan oleh proses penyejatan yang berlaku pada dinding labu sayung, menurut satu kajian teori yang pernah dijalankan di salah sebuah universiti tempatan. Namun, kadar penyejukan air di dalam labu sayung juga dipengaruhi oleh beberapa faktor lain seperti  kelembapan udara, ketebalan dinding labu dan jenis tanah liat yang digunakan untuk membuatnya.

Labu sayung yang diperbuat daripada tanah liat

Menarik, bukan? Kedua-dua fenomena di atas menerangkan kesan penyejukan yang disebabkan oleh bahan yang digunakan iaitu tanah liat. Proses sains yang terlibat untuk kedua-dua keadaan adalah berbeza, membuktikan bahawa tanah liat memang istimewa!

Posted by Ayu
Learning Specialist, Petrosains

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