Science: Technoquest

Questions and answers provided by Science Line's Dial-a-Scientist on 0345 600444. Questions for this column can be submitted by e-mail to sci.net@campus.bt.com

Q When a person is floating (eg in a swimming bath) and tenses their muscles, the body begins to sink. Why? (asked by Irene Palmer)

The only factor that will affect buoyancy is the weight (or amount) of air in the person under water - inhalation makes you go up and exhalation makes you go down. This is standard practice in diving. Tensing your muscles without breathing will not affect your buoyancy per se, though it might perhaps change your centre of buoyancy (ie by moving your diaphragm), resulting in a small displacement. Or you might unconsciously tense one set of muscles slightly more than another - which would affect your orientation in the water, and so possibly your position. Or by tensing your muscles, you might actually move your arms and legs, albeit slightly and without your knowledge. This would change the relative positions of your centre of gravity and centre of buoyancy, causing a small change in position.

However, all the movements described above would be slight, and they would certainly not cause you to sink. Experts at the National Sports Medical Institute and several diving schools agree: it simply doesn't happen. So they wonder - are you sure you aren't breathing out when you tense your muscles?

Q What's actually inside a bacterium?

Bacteria are simple cells; they do not have a distinct nucleus and they do not have many of the organelles (such as mitochondria, chloroplasts, and endoplasmic reticulum) that a higher organism's cells have. The size and shape of bacteria varies according to their type, but they all have a cell wall, a cell membrane and a rather untidy mass of DNA in the middle of their cytoplasm. The cytoplasm itself is granular and not organised into compartments - enzymes and the protein-making ribosomes exist freely. Some bacteria have long hair-like structures on their outer surface called flagellae, which are important in movement: they can be rotated to act like a propeller, moving the bacterium about in the liquid in which it lives.

Q Are there sounds you can't hear?

Yes. A young child's ears can hear up to 25,000 hertz or more - the pitch (frequency) used by bats hunting for insects to eat. As we get older, we can only hear lower frequencies: by 13, most people can only hear sounds below 20,000 Hz. Adults, especially those who have abused their hearing by working in noisy places, lose even more of the top frequencies, and some retired people can only hear sounds below 5,000 Hz. Luckily, most of the energy in speech is in the range 300 - 3,000 Hz, so nearly everyone can still communicate. Most people's ears are most sensitive to sounds around 3,000 Hz. Maybe it's no coincidence that this is the pitch of a smoke alarm - and a baby crying.

Low-frequency sounds below about 100 Hz feel more like a vibration than a note. The transformers in electricity substations vibrate at 100 Hz; you'll need to listen carefully, as your ears don't respond so well to such low frequencies, which sound more like a buzz than a note. A bee's buzz, for example, is about 20 Hz.

Q Silicon is similar to carbon. Why are there no life forms based on silicon?

Silicon is unsuitable because, although it is a valency IV element like carbon, the Si-Si covalent bond is not strong enough for it to form long stable chains, unlike the C-C bond. Silicon cannot therefore form molecules of the complexity needed to make up cellsn

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

Suggested Topics
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebooksAn unforgettable anthology of contemporary reportage
Arts and Entertainment
From Mean Girls to Mamet: Lindsay Lohan
theatre
Sport
Nathaniel Clyne (No 2) drives home his side's second goal past Arsenal’s David Ospina at the Emirates
footballArsenal 1 Southampton 2: Arsène Wenger pays the price for picking reserve side in Capital One Cup
News
Mike Tyson has led an appalling and sad life, but are we not a country that gives second chances?
peopleFormer boxer 'watched over' crash victim until ambulance arrived
Arts and Entertainment
Geena Davis, founder and chair of the Geena Davis Institute on Gender in Media
tv
News
i100
Travel
travelGallery And yes, it is indoors
Life and Style
tech
Arts and Entertainment
The Tiger Who Came To Tea
booksJudith Kerr on what inspired her latest animal intruder - 'The Crocodile Under the Bed'
News
i100
Arts and Entertainment
British actor Idris Elba is also a DJ and rapper who played Ibiza last summer
film
News
Alan Bennett criticised the lack of fairness in British society encapsulated by the private school system
peopleBut he does like Stewart Lee
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

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

iJobs Job Widget
iJobs Media

Account Executive/Sales Consultant – Permanent – Hertfordshire - £16-£20k

£16500 - £20000 Per Annum: Clearwater People Solutions Ltd: We are currently r...

IT Application Support Engineer - Immediate Start

£28000 per annum: Ashdown Group: IT Software Application Support Analyst - Imm...

Senior Management Accountant

£40000 - £46000 per annum: Sauce Recruitment: Global publishing and digital bu...

Semi Senior Accountant - Music

£30000 - £35000 per annum: Sauce Recruitment: A successful, Central London bas...

Day In a Page

Syria air strikes: ‘Peace President’ Obama had to take stronger action against Isis after beheadings

Robert Fisk on Syria air strikes

‘Peace President’ Obama had to take stronger action against Isis after beheadings
Will Lindsay Lohan's West End debut be a turnaround moment for her career?

Lindsay Lohan's West End debut

Will this be a turnaround moment for her career?
'The Crocodile Under the Bed': Judith Kerr's follow-up to 'The Tiger Who Came to Tea'

The follow-up to 'The Tiger Who Came to Tea'

Judith Kerr on what inspired her latest animal intruder - 'The Crocodile Under the Bed' - which has taken 46 years to get into print
BBC Television Centre: A nostalgic wander through the sets, studios and ghosts of programmes past

BBC Television Centre

A nostalgic wander through the sets, studios and ghosts of programmes past
Lonesome George: Custody battle in Galapagos over tortoise remains

My George!

Custody battle in Galapagos over tortoise remains
10 best rucksacks for backpackers

Pack up your troubles: 10 best rucksacks for backpackers

Off on an intrepid trip? Experts from student trip specialists Real Gap and Quest Overseas recommend luggage for travellers on the move
Secret politics of the weekly shop

The politics of the weekly shop

New app reveals political leanings of food companies
Beam me up, Scottie!

Beam me up, Scottie!

Celebrity Trekkies from Alex Salmond to Barack Obama
Beware Wet Paint: The ICA's latest ambitious exhibition

Beware Wet Paint

The ICA's latest ambitious exhibition
Pink Floyd have produced some of rock's greatest ever album covers

Pink Floyd have produced some of rock's greatest ever album covers

Can 'The Endless River' carry on the tradition?
Sanctuary for the suicidal

Sanctuary for the suicidal

One mother's story of how London charity Maytree helped her son with his depression
A roller-coaster tale from the 'voice of a generation'

Not That Kind of Girl:

A roller-coaster tale from 'voice of a generation' Lena Dunham
London is not bedlam or a cradle of vice. In fact it, as much as anywhere, deserves independence

London is not bedlam or a cradle of vice

In fact it, as much as anywhere, deserves independence
Vivienne Westwood 'didn’t want' relationship with Malcolm McLaren

Vivienne Westwood 'didn’t want' relationship with McLaren

Designer 'felt pressured' into going out with Sex Pistols manager
Jourdan Dunn: Model mother

Model mother

Jordan Dunn became one of the best-paid models in the world