Sometimes I get into bed and realise that I've filled up my hot water bottle with water that is too hot. I then add a little water from a nearby jug which is at room temperature. This cools down the temperature immediately, but the hot water I filled it with is still in the hot water bottle. So does the total amount of heat I get over the whole night change?

As a child, if I was hot at night I would turn my pillow over to find it cool and the provider of temporary relief.

I only rarely feel a need to get that cool sensation these days, but why would the pillow be cool?

Brendan Reilly, Dublin, Ireland

The hot water in my house takes a moment to come through when turning on a tap or the shower.  While heating up, the noise of the water hitting the sink etc changes pitch as it changes from cold to hot.  Why is this?

Specifically would an object with said increased electromagnetic bonds etc. exhibit appearances of being colder than they actually were due to the increased energy required to excite them?

Last night I went out for a meal in a nice restaurant with my boyfriend. After a three course meal with two units of alcohol we drove home. We both felt very cold, despite being well wrapped up in a relatively warm car. On closer introspection, I realised that all my muscles were extremely tense, and I wasn't actually all that cold. I was completely unable to relax physically, even though I was totally at ease emotionally. My boyfriend reported the same sensation. I recall feeling the same way on many occasions after leaving restaurants.

Can anybody offer an explanation or indeed a remedy?

Over our Christmas barbecue – it was 35 °C here on 25 December – we started an argument. If it was raining (which it wasn't) which would rust faster, a scalding hot barbecue or a cold one, presuming they were made out of an iron-containing material?

Jayne Millington, Perth, Western Australia

I look after a pendulum clock at the University of Cambridge which I hope will achieve an accuracy of less than 1 second of error per year (www.trin.cam.ac.uk/clock). It has a temperature-compensated pendulum, but is sensitive to air pressure variation.

If the mean global temperature was to rise by, say, 4 °C, would there be any change to mean air pressure at sea level? Put simply, would global warming cause the clock to speed up or slow down?

Hugh Hunt, Keeper of the Clock, Trinity College, University of Cambridge, UK

I was walking along a canal several days ago, and, the UK weather being what it is at the moment, the canal was frozen. However under all the bridges that crossed the canal, whether footbridge or road bridge, the water was unfrozen. What is it about the bridges that stops the water under them from freezing?