Dear all,

After having cooked about 40 crêpes (I'm French), I put them in a plate (whose edges are higher than the center of it) in order to form a pile.

The crepes at the top of the pile are curved, just like on this picture.

I'm sure it is due to the shape of the plate combined with gravity on top of the pile (the crepes are pulled down in their center of gravity, like the hypothetical ball on the image) but my roommate thinks that the crepes have cooked less in the middle than on the edges, explaining the shape. I'm pretty convinced that with truly uniform crepes the result would be the same. What is your explanation ?

As I've grown up i have been told to eat 5 portions of fruit or veg a day. However, if I have 5 of the same fruit or veg it doesnt count, this bring up 2 questions. The first is What is it in particular we are getting from the fruit and veg. Secondly whats wrong with 5 of the same? Thanks

Prematurely overcome by the holiday spirit, we failed to send a round-up last week. Apologies for that. One of the most popular questions from that week – also with a holiday flavour – was what to do during a lightning storm at the beach. Are you safer on the beach or in the water? The discussion contains a fair bit of disagreement, but some great tips for optimum lightning-avoidance behaviour.

This week's questions started with whether the wind affects sound waves (it does, but not in the way you might expect), and whether the foods we crave are the ones our bodies actually need (let's hope so).

Here's one for the physics-minded: ever wondered why most rocket launch pads are sited near the equator? It's to make the most of the rotational velocity of the Earth's surface, which is greatest at the equator. But can you think of any other ways we exploit this tremendous energy source? So far, not many readers can.

If you've ever been caught by brambles while walking in the countryside, you might be curious why the thorns of roses and blackberries are designed to catch animals rather than repel them. Could it be that roses are actually carnivorous?

Finally, August is the month for… meteor-hunting. The Perseid meteor shower is at its height on 12 August. One of our readers reckons he can hear meteors. Is that possible?

Enjoy your weekend.

Michael (acting for Kat)

I've googled food cravings and it's mostly about dieting. I'm interested in whether the body actually knows that certain foods contain required nutrients, vitamins etc.. If I'm low on vitamin C will I suddenly fancy oranges? Has the body somehow registered, from previous consumption of oranges, that this is just the thing I need?

Why might a pregnant woman eat coal? She's never eaten it before and surely it doesn't contain anything absent in a balanced diet?

Can there be some innate knowledge? It seems fanciful to suggest it, but then how do cuckoos know where Africa is?

When I eat nuts I can get severe trapped wind and spicy food can give me heartburn as well as alcohol giving me migraines but I am impervious to such effects at other times

Whilst the oven is on cooking what I fancy for my dinner I’ve always filled any empty shelves with food that could do with being baked and then frozen it for another day with the belief that I am saving energy by using up what would otherwise be wasted space in a hot oven, however, my question is this: am I in fact wasting energy by placing items upon an empty shelf that will now absorb energy to cook, energy that the oven must work to replace? Would it have been more efficient to leave the shelf empty so the oven needs only maintain the temperature?

What I mean by that is, when you eat or drink something (eg. a chilli) sometimes you only get the spicyness after a while. This also happens with cranberry juice- you get a bitter aftertaste.

Why does this happen?

The other day I cooked some egg pasta in salted water and left the pot on the stove. I was away for a couple of days afterward and was surprised on return at the extent of the bacteria that had grown in the slurry at the bottom of the pot. Can anyone identify the bacteria from the photo in particular the red blooms?