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Q. What effect does colour have on your mood?

A. No conclusive research seems to have been done on this topic. In some tests, colours had absolutely no effect on mood. In others, definite effects were seen. People tended to feel more tired after filling in a form printed on red paper than they did after filling in one on green paper. Workers in a red office apparently make fewer mistakes than workers in a green office but they feel much more stressed-out. Young children seem to be happier in a pink room, rather than a blue one. So, some research says colour does affect mood, and some says it doesn't.

Q. What generates the noise of thunder?

A. A lightning flash heats the air around it to about 1,000C. This is about a sixth as hot as the surface of the Sun. As things become hot they expand. This rapid heating of the air causes it to expand quickly resulting in a shockwave that rushes out as a sound wave from the lightning bolt. It is this sound wave that is the thunder. The reason we hear different types of thunder - the long roll or the short crack - is due to the path the lightning takes. Imagine a flash that starts a kilometre above our heads and travels diagonally to hit the Earth a kilometre from our feet. Every point on that path is (very roughly) the same distance from us so the sound from every point of the flash hits us at about the same time. This makes a kind of loud "crack". Now imagine a flash that starts about a kilometre up and ends close to our feet. The sound from the start of the flash's path has to travel much further than the sound from the end and will, as a result, reach us much later. This creates the long, slow roll of thunder.

Q. How do you use the hands of a clock to find North?

A. Point the hour hand of the watch at the Sun. Half way between the hour hand and 12 o'clock is South. North is the opposite direction.

Q. The Earth is tilted at an angle of about 23 degrees to the vertical. How would life be affected if it were not tilted at all?

A. This tilt is responsible for the seasons in the northern and southern hemispheres. At the equator the tilt has less effect, so if the tilt was removed we could all expect constant 12-hour days and (depending on local geography) rather pleasant equatorial type weather.

Q. Why do we cry?

A. It seems that crying in an emotional context is a social signal, much like smiling or frowning. It is instinctive behaviour that tells other people how we're feeling. It probably serves no physiological function.

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