Question Corner

Sound of train

QUESTION : How come we do hear the sound of train whistle and the siren during cold months and not during other times?

N. Sankaran, Coimbatore, T.N.

ANSWER 1: Sound does not travel through vaccum. It needs medium to propagate. It travels faster in medium of lesser density.

Water vapour is lighter than air. As a result of it density of air decreases as moisture content of air increases. Decrease in density causes increase in sound velocity. So the velocity of sound in humid air is more than the velocity of sound in dry air.

N. Ganesh, Chennai

ANSWER 2: Sound produced by any source is influenced by pressure, temp, humidity, moisture, wind etc. In cold months i.e. during winter the air in atmosphere is a mixture containing moisture. Moist air means a mixture of dry air & water vapour. For same temperature & pressure density of water vapour is less than dry air. So, water vapour present in air reduces the density of air. Due to this reason, sound travels faster in a less dense gas than denser gas.Since, in winter season moisture content is more its presence makes the sound to travel faster than other times. Hence, sound can be heard more clearly in cold times than other times.

S. Sharath, Bangalore

More on maintaining body temperature

QUESTION : How does the body normally maintain the temperature at 98 degree Fahrenheit ?

K. Anantha Narayanan, Kanyakumari, T.N.

ANSWER : Besides the answers given by K. Vaitheeswaran (Tuticorin, T.N) and R. Subramanian (Trichy, T.N) there is also ``thermodynamic'' reason in addition to the biological (Neuroendocrine regulation) reasons.

37 degree Celsius (98 degree Fahrenheit) is the optimum temperature at which all the metabolic processes take place quite actively and steadily. Even a slight change from 37 degree Celsius could cause some hindrance to certain metabolic activities of our body. Fever is one such example. It is the heat capacity of water responsible for maintaining the body temperature constantly at 98 Fahrenheit and also it known that about 72-75 per cent of water content is present in an average human body.

Heat capacity, as the term itself, explains that it is the ability to hold the heat energy (i.e.) it is the energy required to raise the temperature of 1 g of a substance by 1 degree celsius. Hence, large heat capacity implies large energy has to be supplied for unit degree raise in the temperature.

The higher heat capacity of water with respect to our body can be understood from the following observation.

``It is known that every body (irrespective of living or non- living) `radiates' energy depending on their body temperature (consequence of Wien's Law).'' Hence every human body radiates energy (where the body's temperature being 37 degree Celsius).

On dipping our finger in water at room temperature, we feel it to be cool, though the water is at room temperature. Thus, the heat capacity of the water is so high with respect to the human body that it absorbs the heat radiated by the body, thereby making it cool.

Hence, it is the ``heat capacity'' of water responsible for the constant maintenance of the body temperature at 98 degree Fahrenheit. (The ``heat capacity'' concept was published in Journal of Chemical Education of January, 1998 issue.)

V. Sabareesh, Pondicherry, T.N.

This Week's Questions

Why do like poles repel and unlike poles react in a magnet?

C.Valli Ananthanarayanan, Kankakumari, T.N.

What is static electricity? Why and how is it created?

R.P.Rammohan, Hyderabad

How is blotting paper and tissue paper different from ordinary paper?

K.Shyam, Kozhikode

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