- Email: [email protected]
Wave goodbye
Last words past and present at newscientist.com/lastword
THE LAST WORD Slick thinking Why are dispersants used to treat oil spills? Wouldn’t a coagulant simplify containment and clean up?
n Coagulants are sometimes used to treat turbidity, or cloudiness, in water. This causes the particles responsible to coalesce, or flocculate, making them easier to remove by precipitation or filtration. When oil is in water, the two form a colloid – a solution in which one substance of microscopically dispersed insoluble particles is suspended throughout another. Colloidal particles do not usually flocculate on their own because they often carry an electric charge, thus repelling each other. Coagulants carry an opposite charge to neutralise the colloid, allowing flocculation. However, the hydrocarbon molecules that constitute oil spills are non-polar, carrying no electric charge, so do not mix with electrically polarised water molecules or coagulants. Dispersants, such as detergent, have a split personality. Their molecules have a long, non-polar tail and a short, electrically charged head. The tails dissolve in oil to form microscopic droplets called micelles, from which heads stick out into the water, allowing mixing and thus easier dispersal. The micelles then disperse to hopefully be biodegraded. However, oil micelles can cause damage. You need look no further
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
than the economic and environmental problems caused by the Deepwater Horizon disaster of 2010 in the Gulf of Mexico. About 7 million litres of dispersant were used to combat this spill. Sadly, a dispersant can be more toxic than the oil it dissipates – and worse, can act in synergy with the oil, causing toxicity many times greater than the sum of the individual toxicities of the oil and dispersant. David Muir Science Department Portobello High School Edinburgh, UK
Wave goodbye Sound waves fade over distance. However, we can see light waves arriving from billions of light years away. Why don’t incoming light waves dissipate before they reach us?
n The answer stems from the fact that light energy is not dissipated as it travels through the vacuum of space, whereas sound cannot travel through a vacuum and needs a material in order to propagate. When sound or light waves pass through material, the matter takes a toll. Even in transparent material, light is absorbed and the amount lost often depends on the light’s wavelength. In the ocean, for example, a large fraction of the red end of the visible spectrum dissipates within about 10 metres of the surface – and not much
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
light of any wavelength reaches depths greater than 50 metres, even in very clear water. By contrast, sound usually suffers less attenuation through water than light does. Certainly, a submerged scuba diver will hear the sound of an engine and rotating propeller even if the boat responsible cannot be seen. Unless it is absorbed by an object blocking the way, sound or light from a point source spreads out in all directions, and its energy expands over the surface of an imaginary sphere, which gets bigger with time. So part of the reason why sound (or light) seems to fade with distance from the source is because its energy is being spread over a greater surface area. Of course, if stars and galaxies did not radiate such prodigious amounts of light energy, they would not be visible from billions of light years away. Mike Follows Sutton Coldfield, West Midlands, UK
This week’s questions Divide and rule
I saw this tree in Austria over the summer (see photos). The trunk seemed to divide near the base and became almost three separate trees as it climbed higher. What species is this, and is it a normal occurrence? If so, what purpose does the division serve? Alan Friel Cork, Ireland
Long in the tooth
My dentist says that dental enamel is never replenished and we have to make do with the adult set of teeth throughout our grown-up lives. I can’t believe that after some 80 years of chomping and grinding, my teeth are still the same shape, without apparent signs of wear. Is he right? If so, why am I generally still toothily intact? John Everest Pinner, Middlesex, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Slick thinking Why are dispersants used to treat oil spills? Wouldn’t a coagulant simplify containment and clean up?
n Coagulants are sometimes used to treat turbidity, or cloudiness, in water. This causes the particles responsible to coalesce, or flocculate, making them easier to remove by precipitation or filtration. When oil is in water, the two form a colloid – a solution in which one substance of microscopically dispersed insoluble particles is suspended throughout another. Colloidal particles do not usually flocculate on their own because they often carry an electric charge, thus repelling each other. Coagulants carry an opposite charge to neutralise the colloid, allowing flocculation. However, the hydrocarbon molecules that constitute oil spills are non-polar, carrying no electric charge, so do not mix with electrically polarised water molecules or coagulants. Dispersants, such as detergent, have a split personality. Their molecules have a long, non-polar tail and a short, electrically charged head. The tails dissolve in oil to form microscopic droplets called micelles, from which heads stick out into the water, allowing mixing and thus easier dispersal. The micelles then disperse to hopefully be biodegraded. However, oil micelles can cause damage. You need look no further
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
than the economic and environmental problems caused by the Deepwater Horizon disaster of 2010 in the Gulf of Mexico. About 7 million litres of dispersant were used to combat this spill. Sadly, a dispersant can be more toxic than the oil it dissipates – and worse, can act in synergy with the oil, causing toxicity many times greater than the sum of the individual toxicities of the oil and dispersant. David Muir Science Department Portobello High School Edinburgh, UK
Wave goodbye Sound waves fade over distance. However, we can see light waves arriving from billions of light years away. Why don’t incoming light waves dissipate before they reach us?
n The answer stems from the fact that light energy is not dissipated as it travels through the vacuum of space, whereas sound cannot travel through a vacuum and needs a material in order to propagate. When sound or light waves pass through material, the matter takes a toll. Even in transparent material, light is absorbed and the amount lost often depends on the light’s wavelength. In the ocean, for example, a large fraction of the red end of the visible spectrum dissipates within about 10 metres of the surface – and not much
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
light of any wavelength reaches depths greater than 50 metres, even in very clear water. By contrast, sound usually suffers less attenuation through water than light does. Certainly, a submerged scuba diver will hear the sound of an engine and rotating propeller even if the boat responsible cannot be seen. Unless it is absorbed by an object blocking the way, sound or light from a point source spreads out in all directions, and its energy expands over the surface of an imaginary sphere, which gets bigger with time. So part of the reason why sound (or light) seems to fade with distance from the source is because its energy is being spread over a greater surface area. Of course, if stars and galaxies did not radiate such prodigious amounts of light energy, they would not be visible from billions of light years away. Mike Follows Sutton Coldfield, West Midlands, UK
This week’s questions Divide and rule
I saw this tree in Austria over the summer (see photos). The trunk seemed to divide near the base and became almost three separate trees as it climbed higher. What species is this, and is it a normal occurrence? If so, what purpose does the division serve? Alan Friel Cork, Ireland
Long in the tooth
My dentist says that dental enamel is never replenished and we have to make do with the adult set of teeth throughout our grown-up lives. I can’t believe that after some 80 years of chomping and grinding, my teeth are still the same shape, without apparent signs of wear. Is he right? If so, why am I generally still toothily intact? John Everest Pinner, Middlesex, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything