Science: Technoquest

The kneejerk reaction/ Most expensive metals/ Shapes - what's in a name?/ Our synchronously rotating moon

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

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

Q Why do doctors on TV tap the knee of a patient to see if their leg jerks?

They do this to test whether the knee jerk reflex - which helps the body to control the movement of the legs during running - is working properly. If it is, this gives the "doctor" information about how well the person's nervous system is working, and they test to see if it is working on both sides of the body. A reflex is a rapid, automatic response to a stimulus: pulling your hand away from a hot pan-handle is a reflex action. A simple reflex involves communication between neurones in the peripheral nervous system and the spinal cord. The brain may be informed, but does not take part in the response.

Reflexes can also help to co-ordinate complex muscular events, such as swallowing. The knee-jerk is a "stretch" reflex - one of many which work together to help us maintain an upright posture. You can test it by holding your knee suspended, leg down, and tapping the leg just below the kneecap. Your lower leg should lift automatically.

Q What are the most expensive elements?

It depends to some extent on what state they are sold in - foil, wire, powder, rod, etc. Generally speaking, though, the most expensive are osmium, platinum, iridium, gold and europium.

Q How are mathematical shapes named?

Shapes are named from the standard Greek roots for numbers, according to the number of sides: pentagon (5), hexagon (6), heptagon/ septagon (7), octagon (8), enneagon/ nonagon (9), decagon (10), hendecagon/ undecagon (11), dodecagon (12).

Three- and four-sided figures are so familiar that we usually talk of the triangle and quadrilateral rather than the formal "trigon" and "tetragon". But most names for large numbers of sides are not used: a 27-sided shape is just called "a 27-sided polygon" - apart from the 15-sided pendecagon/ quindecagon and 100-sided chiliagon.

Q Is it just a coincidence that the Moon takes the same amount of time to rotate as it does to go round the Earth?

The two rotational rates are not a coincidence. The Moon is locked in what's known as a "synchronous rotation". The Earth raises body tides on the Moon (basically, it stretches it) which are about 20 times greater than body tides on the Earth. The enormous energy dissipation that results has slowed the rotation of the Moon to result in an equilibrium, whereby the Moon's rotation (27 days) is the same as the time it takes to revolve around the Earth. Thus it always presents the same face to us.

As a consequence of tidal forces, the Moon is actually moving away from the Earth. The angular momentum of the Earth-Moon system must remain constant; the Earth's momentum is decreasing, owing to tides raised on its surface; and, in order to conserve momentum, the Moon increases its angular momentum by moving away.

Some of the satellites of the outer planets (Jupiter Saturn Uranus and Neptune) have also become trapped in synchronous orbits.

Q Is it true that cold weather stimulates urination?

Cold weather of itself would not directly stimulate urine production or excretion. But it does lead to reduced sweat production, so proportionally more water has to be excreted via the kidneys - hence, more visits to the toilet.

Questions and answers provided by Science Line's Dial-a-Scientist (0345 600444)

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment

ebooksNow available in paperback
Arts and Entertainment

ebooks
Arts and Entertainment
Mark, Katie and Sanjay in The Apprentice boardroom
TV
Arts and Entertainment

Film The critics but sneer but these unfashionable festive films are our favourites

Arts and Entertainment
Frances O'Connor and James Nesbitt in 'The Missing'

TV We're so close to knowing what happened to Oliver Hughes, but a last-minute bluff crushes expectations

Arts and Entertainment
Joey Essex will be hitting the slopes for series two of The Jump

TV

Who is taking the plunge?
Arts and Entertainment
Katy Perry as an Ancient Egyptian princess in her latest music video for 'Dark Horse'

music
Arts and Entertainment
Dame Judi Dench, as M in Skyfall

film
Arts and Entertainment
Morrissey, 1988

TV
Arts and Entertainment
William Pooley from Suffolk is flying out to Free Town, Sierra Leone, to continue working in health centres to fight Ebola after surviving the disease himself

music
Arts and Entertainment
The Newsroom creator Aaron Sorkin

TV
Arts and Entertainment
Matt Berry (centre), the star of Channel 4 sitcom 'Toast of London'

TVA disappointingly dull denouement
Arts and Entertainment
Tales from the cryptanalyst: Benedict Cumberbatch in 'The Imitation Game'

film
Arts and Entertainment
Pixie Lott has been voted off Strictly Come Dancing 2014

Strictly
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.

    Jeb Bush vs Hillary Clinton: The power dynamics of the two first families

    Jeb Bush vs Hillary Clinton

    Karen Tumulty explores the power dynamics of the two first families
    Stockholm is rivalling Silicon Valley with a hotbed of technology start-ups

    Stockholm is rivalling Silicon Valley

    The Swedish capital is home to two of the most popular video games in the world, as well as thousands of technology start-ups worth hundreds of millions of pounds – and it's all happened since 2009
    Did Japanese workers really get their symbols mixed up and display Santa on a crucifix?

    Crucified Santa: Urban myth refuses to die

    The story goes that Japanese store workers created a life-size effigy of a smiling "Father Kurisumasu" attached to a facsimile of Our Lord's final instrument of torture
    Jennifer Saunders and Kate Moss join David Walliams on set for TV adaptation of The Boy in the Dress

    The Boy in the Dress: On set with the stars

    Walliams' story about a boy who goes to school in a dress will be shown this Christmas
    La Famille Bélier is being touted as this year's Amelie - so why are many in the deaf community outraged by it?

    Deaf community outraged by La Famille Bélier

    The new film tells the story of a deaf-mute farming family and is being touted as this year's Amelie
    10 best high-end laptops

    10 best high-end laptops

    From lightweight and zippy devices to gaming beasts, we test the latest in top-spec portable computers
    Michael Carberry: ‘After such a tough time, I’m not sure I will stay in the game’

    Michael Carberry: ‘After such a tough time, I’m not sure I will stay in the game’

    The batsman has grown disillusioned after England’s Ashes debacle and allegations linking him to the Pietersen affair
    Susie Wolff: A driving force in battle for equality behind the wheel

    Susie Wolff: A driving force in battle for equality behind the wheel

    The Williams driver has had plenty of doubters, but hopes she will be judged by her ability in the cockpit
    Adam Gemili interview: 'No abs Adam' plans to muscle in on Usain Bolt's turf

    'No abs Adam' plans to muscle in on Usain Bolt's turf

    After a year touched by tragedy, Adam Gemili wants to become the sixth Briton to run a sub-10sec 100m
    Calls for a military mental health 'quality mark'

    Homeless Veterans campaign

    Expert calls for military mental health 'quality mark'
    Racton Man: Analysis shows famous skeleton was a 6ft Bronze Age superman

    Meet Racton Man

    Analysis shows famous skeleton was a 6ft Bronze Age superman
    Garden Bridge: St Paul’s adds to £175m project’s troubled waters

    Garden Bridge

    St Paul’s adds to £175m project’s troubled waters
    Stuff your own Christmas mouse ornament: An evening class in taxidermy with a festive feel

    Stuff your own Christmas mouse ornament

    An evening class in taxidermy with a festive feel
    Joint Enterprise: The legal doctrine which critics say has caused hundreds of miscarriages of justice

    Joint Enterprise

    The legal doctrine which critics say has caused hundreds of miscarriages of justice
    Freud and Eros: Love, Lust and Longing at the Freud Museum: Objects of Desire

    Freud and Eros

    Love, Lust and Longing at the Freud Museum