UNDER THE MICROSCOPE: Summer quiz

LEWIS WOLPERT POSES SOME SCIENCE BRAIN-TEASERS

I hope that my readers are so relaxed that they will want a little mental stimulation. So here are some puzzles that you might, I hope, find both amusing and interesting.

1 Why are your left and right sides reversed when you look in a mirror, but not your head to your feet?

2 Why do wheels make it easier to move an object?

3 There is only one correct scientific explanation for any set of phenomena. True or false?

4 You have a 100lb sack of potatoes; they are made up of 99 per cent water. You leave them outside for a day or two till they are only 98 per cent water. So how much does the sackful weigh now?

5 Why do tapirs and parrots in the Peruvian jungle regularly eat clay?

6 Given an evenly weighted coin with heads and tails, spun six times, which sequence is most likely: HHHHHHH; TTTTTT; HTHTHT?

7 What role did basic science play in the invention of the aeroplane and steam engine?

8 Why do healthy old elephants die?

9 If I go into a perfectly flat field a with two bullets and fire one from a gun horizontally and drop the other at exactly the same time, which hits the ground first?

10 You are in a small boat in a swimming-pool and there is a stone in the boat.You throw the stone into the water. Does the water-level in the pool rise or fall or stay the same?

11 It is a very hot day so you open the refrigerator in your kitchen to cool the room - is this a good idea?

12 In a future society, the postal service becomes so corrupt that anything sent unlocked will definitely be stolen by the postmen. The only way to guarantee an item arriving is to put it into a case with a locked padlock on it. You want to send some secret documents and money to a friend through the post. How can you do it? There are no tricks to this puzzle - all you need is padlocks and keys, and apart from the post there is no other way to transport keys.

Now the answers:

1 Left and right have no meaning on their own but are defined with respect to up/down and front/back. If one of these axes is reversed so left/right will be. The front/back axis is reversed when you look in a mirror.

2 Wheels work because they reduce friction.

3 True, even if it is difficult to find out which is the correct explanation. Note that light can be both a particle and a wave - just one explanation.

4 Just 50lb; if there is one unit of potato in 50lb, the water content is 98 per cent.

5 The local explanation is that is helps them deal with toxins in their diet.

6 Too easy - they are all equally probable; remember that the coin has no memory.

7 None - they were initially invented by imaginative trial and error.

8 They die because their teeth have worn out.

9 They both hit the ground at the same time - the rate of fall is not influenced by horizontal motion.

10 As Archimedes would have told you, the water level falls; when the stone is in the boat it displaces its own weight of water but that is more than the water it displaces when it is in the pool, as it is denser than water.

11 No, as the machine cooling of the refrigerator will actually make the room hotter.

12 Put the message in a bag, padlock it and send it to your friend. The friend adds another padlock to the bag and sends it back to you; and you remove your padlock and send the bag back to the friend, who then unlocks it.

Have a happy summer.