Have you wondered why the flame of a burning candle or matchstick or bonfire always rises upwards and never goes downwards or sideways? All fuels such as wood, matchstick or candle, contain carbon and hydrogen. When these substances burn, carbon combines with oxygen of the air and forms carbon dioxide. Similarly, hydrogen also combines with oxygen and forms water. Some other gases are also produced. As a result of this burning process, these substances produce heat and light. The gases produced during combustion are lighter than air so they rise up and so does the flame. If you lightly blow the flame you will notice that it flickers. This is because, the air you blow disturbs the burning gases, so the flame is also disturbed. In the absence of any such disturbance the flame remains steady.