Tuesday 04 July 1995
A. As water is heated, its molecules become more excited as they gain extra heat energy and move around a lot more. At a certain temperature, some molecules have enough energy to change into a gas and become water vapour. This change can take place within the body of water. Since the water vapour is less dense than the liquid, it rises in the form of expanding bubbles until it reaches the surface of the water and escapes.
Q. How does amount of body fat relate to fitness?
A. It depends on the sport. Athletes such as runners and high-jumpers try to minimise body fat, which they see as dead weight. It requires energy to move it, but does not increase the body's power output. In aerobic sports such as cycling where weight is not especially important, athletes still try to reduce body fat. This is because performance in aerobic sports is often limited by the maximal rate of oxygen uptake. Fat tissue is actively metabolising, using oxygen and requiring blood circulation. If fat is lost, the oxygen and blood flow can be redirected to muscles, which give a higher power output.
Swimmers tend to have higher fat levels than most athletes. This is because fat is less dense than muscle and increases buoyancy. For sumo wrestlers, the advantages of a huge percentage of body fat and weight are quite obvious.
Q. What causes winds?
A. The sun heats air in some regions more than others, causing it to expand and become less dense. It rises and creates a lower pressure in the area below. Air rushes in from the nearest high pressure area to fill the gap, and places between the two pressure zones experience wind.
Q. Why are metals better thermal conductors than glass and wood?
A. A defining property of a metal is its structure. Metals are made of a lattice of positive ions (atoms with one or two electrons missing) in a sea of the missing electrons, which are very mobile and free to conduct electricity and heat. Glass has a structure in which all electrons are firmly attached to atoms, meaning they do not conduct electricity.
Q. Why does salt placed in ice buckets cool wine quicker?
A. Salt lowers the freezing point of ice, causing the ice to melt. But to melt, the ice needs energy. It takes this from the wine, thereby cooling it.
n These questions and answers are provided by Science Line. You can use its Dial-A-Scientist service on 0345 600444.
Actress sees off speculation about her appearance in an amazing way
Powerful images of strays taken moments before being put down
The Washington Post editor helped Bob Woodward and Carl Bernstein bring down President Nixon
Children's bookseller wins The Independent's new author search
- 1 Salisbury ranked seventh-best city in the world to visit in Lonely Planet’s Best in Travel 2015
- 2 Disney announces new female-led film Moana
- 3 Banksy has not been arrested: Internet duped by fake report claiming artist's identity revealed
- 5 Russell Brand threatened with arrest after filming outside Fox News headquarters
Chicago voter tells Obama 'don't touch my girlfriend' – Obama stays super smooth
Oscar Pistorius: The brutal prison life that awaits disgraced athlete
Banksy has not been arrested: Internet duped by fake report claiming artist's identity revealed
Raphael Ravenscroft dead: 'Baker Street' musician who played the most famous saxophone solo for just £27, dies aged 60
Darren Vann: Indiana man arrested for murdering teenage prostitute confesses to six other murders - and police fear more
Cameron is warned 'no possibility' of UK reducing immigration and that bid to bring in quota on migrant workers would be illegal
Residents should throw a street party and mix with immigrant neighbours, councils told
Russell Brand threatened with arrest after filming outside Fox News headquarters
London bus driver 'kicks gay couple off for kissing'
Jose Manuel Barroso warns David Cameron against making 'historic mistake' over immigration reforms
Of course, teenage girls need role models – but not like beauty vlogger Zoella
£300 - £350 Per Day: Clearwater People Solutions Ltd: The role could involve w...
£21000 - £35000 per annum: Randstad Education Cambridge: Qualified secondary s...
£22000 - £36000 per annum + MPR / UPR: Randstad Education Southampton: Our cli...
£28000 - £35000 per annum + negotiable: Sauce Recruitment: We have an exciting...