Question 1: Why do we get tired while running?
Answer 1: To run, we have to move the body fast, and energy is needed for this. Energy is required by the muscles for contraction, to effect these movements. Living cells release energy by aerobic respiration, for which oxygen is needed. The increased muscle action that takes place when running, needs a faster supply of oxygen. For this, we have to increase our breathing rate. But, while running, this is not easy. The resultant difficulty that the body feels, is what we call tiredness.
Question 2: Why does ice melt when taken out of the freezer?
Answer 2: Any substance stays as a solid only till its temperature is below its melting point. For ice, this is 0 degrees C. So ice exists only in such a place like in a freezer where the temperature is usually below 0 degrees C. When taken out of the freezer ice melts (or becomes a liquid), because the temperature that it encounters from its environment is well above its melting point.
Question 3: A flash of lightning can be seen long before the sound of thunder. Why?
Answer 3: Clouds are formed by the collection of a large number of water droplets. The atoms which make up these clouds contain protons and electrons, equally distributed. Due to high winds, these clouds bang onto each other, resulting in the electrons being thrown to one side, with more protons remaining on the other side. It is common knowledge that opposite charges attract. So when the electrons of a side of a cloud, jump onto the positive side ( containing excess protons) of the neighbouring cloud, a huge electric spark occurs, with the emission of a very loud sound. Though both light and sound are produced at the same time, speed of light is much more than speed of sound. That is why the spark of lightning reaches our eyes much earlier than the clap of thunder reaches our ears.
Question 4: Blood coming out of a cut is red at first, but soon turns dark, almost black. Why?
Answer 4: A compound called haemoglobin present in red blood cells, combines with oxygen and forms oxy haemoglobin, which is bright red. This happens only till the blood is in the blood vessels, and is not exposed to air. When the skin is damaged and blood vessels are cut, fresh red blood comes out of the wound. With time, as blood starts drying, the haemoglobin starts getting denatured, and forms other compounds which have a deep brownish colour, which we perceive as almost black.
Question 5: Why are rain clouds grey?
Answer 5: When there is more water vapour in the sky, the clouds gather more water droplets and even ice crystals, because of the very low temperature high up in the sky. This makes the clouds get thicker. The thicker they get, the more light they scatter from the upper side, resulting in less light penetrating through them. So, the particles on the underside of that cloud do not get a lot of light to scatter to your eyes, and so, the base appears grey as you look from the ground below. This effect is more pronounced the larger the water droplets get, just before the water falls from the sky as rain.
Question 6: Why do some doctors advice against using cotton buds or other objects to clean ears?
Answer 6: Applying any tool or a cotton bud inside the ear with hands usually creates a force that pushes any thing including ear wax on the ear drum, and may even cause ear wax to accumulate more on the ear drum. This force may sometimes damage the ear drum, causing pain. It also might cause leakage, causing improper balance, and also difficulty in hearing.
Question 7: The skin of a raw fruit is green, but it turns yellow or orange when it ripens. Why?
Answer 7: The skin of a raw fruit contains the green pigments of chlorophyll 'a' and chlorophyll 'b' in large amounts with very little amounts of yellow xanthophyll and orange carotene. So the green colour predominates and covers the other colours. When it ripens the green chlorophyll gets broken down leaving behind the other coloured pigments, making the ripe fruit yellow or orange.