Science: Archimedes strikes again; the ozone principle

Technoquest

Questions and answers provided by Science Line's Dial-a-Scientist, on 0345 600444

Q Could you just explain Archimedes Principle again? I didn't understand it last time.

The important thing is not to confuse weight (or mass) and volume. When you immerse an object in any liquid, it must move its own volume in liquid out of the way. That displaced volume has a mass, which must be pushed up against the force of gravity. So there are opposing forces: gravity acting downwards on the object's mass, and pressure on the object from the displaced water volume. This second force acts upwards through the object's centre of gravity, and is called the buoyancy force. If the displaced water's weight is more than the weight of the completely immersed object, the object is pushed up until less of it is immersed - so less water is displaced. When the weight of the displaced water equals that of the whole object, it floats. However, if the displaced water weighs less than the object, the object sinks.

Q Why is there a greater loss of ozone over the South Pole compared to the North Pole?

The increased ozone loss over the South Pole is due to the atmospheric conditions over the region. The large land mass of Antarctica sets up a polar vortex, which leads to a trapping of the chlorofluorocarbon molecules (CFCs) in that region of the atmosphere. When the southern polar spring comes and the sun shines again, the solar radiation breaks down the CFCs, releasing radicals (highly reactive atoms and molecules) that destroy the ozone. Hence the greatest ozone loss occurs in only a few weeks around the begining of the polar spring. Over the North Pole, such a vortex cannot occur as the land surface is too small; so there is not such a build-up of CFCs. The northern regions still suffer an ozone loss, but it is less dramatic.

Q How is the skeleton held together?

The bones which make up the skeleton are held together by a support system consisting of skeletal muscles, ligaments, tendons, and cartilage. The skeletal muscles mean we can move whenever we feel like it. Ligaments join one bone to another, across a joint - without ligaments, joints would become dislocated very easily. Tendons join muscles to bones, across a joint. Some tendons are quite large and can be felt easily: the Achilles tendon at the back of the ankle and the two hamstring tendons at the back of the knee joint are good examples. Cartilage, or gristle, is a smooth, tough and flexible substance which is found in joints such as the knee. It covers the ends of bones at joints to allow smooth movement as the bones move against each other.

Q Is it possible to build a chess computer that knows every move so that it wins every time?

Computers have "solved" some simpler games so that they always either win or, at worst, draw. Chess is a much bigger problem. Clearly, at every step of a chess game, there are only a finite (but large) number of possible moves: 20 at the start, and so on. The number of possible sequences of moves to the end of a game is also finite - though of course even larger. So in theory one could "build a chess computer that knows all possible moves". However, the number of possible sequences of moves is astronomically large (400 just for the first two moves, after which it gets really hard), the ultimate speed of computers is limited (for example by the speed of light and therefore communication within the computer), so the shortest possible time needed just to compute all possible moves is many persons' lifetimes. And this does not even consider the time needed to evaluate those moves and to determine the "optimum". So the practical answer is no.

Q How does the technique of using planets to speed up satellites work? Doesn't this slow the planets down?

The planet's gravity is used as a "slingshot" to speed up the satellite on its journey. In the process, the planet does suffer a slight loss of its momentum. But the amount is negligible. For the Voyager flybys of Jupiter, for example, the planet's lost energy resulted in Jupiter's orbit being slowed down by about one foot per trillion years.

You can also visit the technoquest World Wide Web site at http://www.campus.bt.com/CampusWorld/pub/ ScienceNet

Questions for this column can be submitted by e-mail to sci.net@campus.bt.com

Suggested Topics
Arts and Entertainment
Kanye West found himself at the centre of a critical storm over the weekend after he apparently claimed to be “the next Mandela” during a radio interview
music
Arts and Entertainment
Daniel Craig and Rory Kinnear film Spectre in London
film
Arts and Entertainment
Attenborough with the primates
tvWhy BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter
Arts and Entertainment
Drake continues to tease ahead of the release of his new album
music
Arts and Entertainment
Former Communards frontman Jimmy Somerville
music
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment

ebooksNow available in paperback
Arts and Entertainment

ebooks
Arts and Entertainment
Olivia Colman and David Tennant star in 'Broadchurch'

TVViewers predict what will happen to Miller and Hardy
Arts and Entertainment
Kevin Spacey and Robin Wright in season two of the series

Watch the new House of Cards series three trailer

TV
Arts and Entertainment
An extract from the sequel to Fight Club

books
Arts and Entertainment
David Tennant, Eve Myles and Olivia Colman in Broadchurch series two

TV Review
Arts and Entertainment
Old dogs are still learning in 'New Tricks'

TV
Arts and Entertainment
'Tonight we honour Hollywood’s best and whitest – sorry, brightest' - and other Neil Patrick Harris Oscars jokes

Oscars 2015It was the first time Barney has compered the Academy Awards

Arts and Entertainment
Patricia Arquette making her acceptance speech for winning Best Actress Award

Oscars 2015 From Meryl Streep whooping Patricia Arquette's equality speech to Chris Pine in tears

Arts and Entertainment

Oscars 2015 Mexican filmmaker uses speech to urge 'respect' for immigrants

Arts and Entertainment
The Oscar nominations are due to be announced today

Oscars 2015 Bringing you all the news from the 87th Academy Awards

Arts and Entertainment
Lloyd-Hughes takes the leading role as Ralph Whelan in Channel 4's epic new 10-part drama, Indian Summers

TV Review

The intrigue deepens as we delve further but don't expect any answers just yet
Arts and Entertainment
Jason Segal and Cameron Diaz star in Sex Tape

Razzies 2015 Golden Raspberry Awards 'honours' Cameron Diaz and Kirk Cameron

Arts and Entertainment
The Oscars ceremony 2015 will take place at the Dolby Theatre in Los Angeles
Oscars 2015A quiz to whet your appetite for tonight’s 87th Academy Awards
Arts and Entertainment
Sigourney Weaver, as Ripley, in Alien; critics have branded the naming of action movie network Movies4Men as “offensive” and “demographic box-ticking gone mad”.
TVNaming of action movie network Movies4Men sparks outrage
Arts and Entertainment
Sleater Kinney perform at the 6 Music Festival at the O2 Academy, Newcastle
musicReview: 6 Music Festival
News
Kristen Stewart reacts after receiving the Best Actress in a Supporting Role award for her role in 'Sils Maria' at the 40th annual Cesar awards
people
News
A lost Sherlock Holmes story has been unearthed
arts + ents Walter Elliot, an 80-year-old historian, found it in his attic,
Arts and Entertainment
Margot Robbie rose to fame starring alongside Leonardo DiCaprio in The Wolf of Wall Street

Film Hollywood's new leading lady talks about her Ramsay Street days

Arts and Entertainment
Right note: Sam Haywood with Simon Usborne page turning
musicSimon Usborne discovers it is under threat from the accursed iPad
Latest stories from i100
Have you tried new the Independent Digital Edition apps?

ES Rentals

    Independent Dating
    and  

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    War with Isis: Fears that the looming battle for Mosul will unleash 'a million refugees'

    The battle for Mosul will unleash 'a million refugees'

    Aid agencies prepare for vast exodus following planned Iraqi offensive against the Isis-held city, reports Patrick Cockburn
    Yvette Cooper: We can't lose the election. There's too much on the line

    Yvette Cooper: We can't lose the election. There's too much on the line

    The shadow Home Secretary on fighting radical Islam, protecting children, and why anyone in Labour who's thinking beyond May must 'sort themselves out'
    A bad week for the Greens: Leader Natalie Bennett's 'car crash' radio interview is followed by Brighton council's failure to set a budget due to infighting

    It's not easy being Green

    After a bad week in which its leader had a public meltdown and its only city council couldn't agree on a budget vote, what next for the alternative party? It's over to Caroline Lucas to find out
    Gorillas nearly missed: BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter

    Gorillas nearly missed

    BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter
    Downton Abbey effect sees impoverished Italian nobles inspired to open their doors to paying guests for up to €650 a night

    The Downton Abbey effect

    Impoverished Italian nobles are opening their doors to paying guests, inspired by the TV drama
    China's wild panda numbers have increased by 17% since 2003, new census reveals

    China's wild panda numbers on the up

    New census reveals 17% since 2003
    Barbara Woodward: Britain's first female ambassador to China intends to forge strong links with the growing economic superpower

    Our woman in Beijing builds a new relationship

    Britain's first female ambassador to China intends to forge strong links with growing economic power
    Courage is rare. True humility is even rarer. But the only British soldier to be awarded the Victoria Cross in Afghanistan has both

    Courage is rare. True humility is even rarer

    Beware of imitations, but the words of the soldier awarded the Victoria Cross were the real thing, says DJ Taylor
    Alexander McQueen: The catwalk was a stage for the designer's astonishing and troubling vision

    Alexander McQueen's astonishing vision

    Ahead of a major retrospective, Alexander Fury talks to the collaborators who helped create the late designer's notorious spectacle
    New BBC series savours half a century of food in Britain, from Vesta curries to nouvelle cuisine

    Dinner through the decades

    A new BBC series challenged Brandon Robshaw and his family to eat their way from the 1950s to the 1990s
    Philippa Perry interview: The psychotherapist on McDonald's, fancy specs and meeting Grayson Perry on an evening course

    Philippa Perry interview

    The psychotherapist on McDonald's, fancy specs and meeting Grayson Perry on an evening course
    Bill Granger recipes: Our chef recreates the exoticism of the Indonesian stir-fry

    Bill Granger's Indonesian stir-fry recipes

    Our chef was inspired by the south-east Asian cuisine he encountered as a teenager
    Chelsea vs Tottenham: Harry Kane was at Wembley to see Spurs beat the Blues and win the Capital One Cup - now he's their great hope

    Harry Kane interview

    The striker was at Wembley to see Spurs beat the Blues and win the Capital One Cup - now he's their great hope
    The Last Word: For the good of the game: why on earth don’t we leave Fifa?

    Michael Calvin's Last Word

    For the good of the game: why on earth don’t we leave Fifa?
    HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

    Scientists hail daily pill that protects against HIV infection

    Breakthrough in battle against global scourge – but will the NHS pay for it?