Velocity

Velocity, in physics, is a vector quantity (it has both magnitude and direction), and is the time rate of change of position (of an object). However, quite often when you read ‘velocity’, what is meant is speed, the magnitude of the velocity vector (speed is a scalar quantity, it has only magnitude). For example: escape velocity (the minimum speed an object needs to escape from a planet, say); note that this can be easily turned into a velocity, by adding ‘in the direction radially out from the center of the planet’, and that this direction is sometimes implied (if not actually stated).

In astronomy, it is often quite straight-forward to measure the component of velocity of a distant object along the line of sight to it, by measuring its redshift. This is a one-dimensional velocity (it has both magnitude and direction – either towards the observer, or away), but only one component of the object’s space motion. In most cases, it is clear from the context what is meant by ‘velocity’; for example, a ‘galaxy rotation curve’ often has ‘velocity’ on the vertical axis, meaning something like the estimated magnitude of the orbital velocity of the stars/gas/dust/plasma in the galaxy, assuming circular orbits. However, if you are not clued in to this context, it is all too easy to misunderstand what ‘velocity’ means!

Perhaps the most common form of Newton’s first law of motion is “In the absence of netforce, a body is either at rest or moves at a constant speed in a straight line”. It is easy to re-write this using the textbook physics definition of velocity: “In the absence of net force, a body’s velocity is constant”.

The word ‘velocity’ is used in many Universe Today stories, with various meanings; Solar System Movements and Positions and Einstein’s Theory of Special Relativity are two Astronomy Cast episodes highly relevant to the definition of velocity;

Velocity is a vector measurement of the rate and direction of motion or, in other terms, the rate and direction of the change in the position of an object. The scalar (absolute value) magnitude of the velocity vector is the speed of the motion. In calculus terms, velocity is the first derivative of position with respect to time.

The most common way to calculate the constant velocity of an object moving in a straight line is with the formula:

r = d / t

where

• r is the rate, or speed (sometimes denoted as v, for velocity, as in this kinematics article)
• d is the distance moved
• t is the time it takes to complete the movement

The SI units for velocity are m / s (meters per second).

Velocity - related terms

Acceleration is the rate of change of velocity as a function of time. It is vector. In calculus terms, acceleration is the second derivative of position with respect to time or, alternately, the first derivative of the velocity with respect to time.

The SI units for acceleration are m / s² (meters per second squared ormeters per second per second).

Inertia is the name for the tendency of an object in motion to remain in motion, or an object at rest to remain at rest, unless acted upon by a force. This concept was quantified in Newton's First Law of Motion.

Speed of light in a vacuum

The speed of light (c) in a vacuum, is exactly 299,792,458 meters per second (ms^-1), which rounds up very nicely to 300,000,000 ms^-1, which scientists write as 3 x 10⁸ ms^-1. 

In more dense media the speed is slower, 

e.g.

1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.

CALCULATIONS

The speed of light, using a very close approximation for calculation purposes, is taken as 3.0 x 10⁸ m/s (metres per second). i.e. 300,000,000 m/s

The greater the refractive index of the medium, the slower the speed of light in that medium/material.

The speed of light in a vacuum [c] divided by the velocity of light in the material [v] equals the refractive index [n] of the material.

Examples

1. calculate the refractive index of space: ^c/_c equals 1

2. water (the speed of light in water is 225,056,264 m/s): ^c/ _225056264 equals 1.333

Inversely, if we know the refractive index of a material, we can calculate the velocity of light through that material, i.e. the speed of light [c] divided by the refractive index [n] equals the velocity of light [v] in that material

Using the example of water, refractive index 1.333 :- 300,000,000 [c] divided by 1.333 [n] equals 225,056,264 [n] i.e. the velocity of light in water is 225,056,264 m/s.

This is ^225,056,264/_300,000,000 ^ths the speed of light, or 0.75 of c.

SOME REFRACTIVE INDICES

• vacuum1.00
• air 1.0003
• water 1.333
• fused quartz 1.4585
• plexiglass 1.51
• crown glass* 1.52
• diamond 2.417
• gallium phosphide 3.50

*Crown glass is a type of glass used in lenses, and has a lower refractive index than flint glass which is also used in lenses.

Is The Speed of Light Constant?

There are a number of senses to the meaning of this question and so there are a number of different answers.  Firstly . . .

Does the speed of light change in air or water?

Yes.  Light is slowed down in transparent media such as air, water and glass.  The ratio by which it is slowed is called the refractive index of the medium and is always greater than one.^*  This was discovered by Jean Foucault in 1850.

When people talk about "the speed of light" in a general context, they usually mean the speed of light in a vacuum.  This quantity is also referred to as c.

Is c, the speed of light in vacuum, constant?

At the 1983 Conference Generale des Poids et Mesures, the following SI (Systeme International) definition of the metre was adopted:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

This defines the speed of light in vacuum to be exactly 299,792,458 m/s.  This provides a very short answer to the question "Is c constant": Yes, c is constant by definition!

Variable Speed of Light

Effect of gravity on measured Speed of Light

Suppose that you have a clock and a ruler (which is not rotating with respect to stars) and that you are not accelerating (inertial). Locally (where you are) you will always measure the speed of light at 299792.458 km/sec. However in the presence of gravity if I am at a different location than yours then I could measure the speed of light at your location to be any value smaller than or greater than 299792.458 km/sec. It depends on where I am and where you are (it depends on locations). So in the presence of gravity the speed of light becomes relative (variable depending on the reference frame of the observer). This does not mean that photons accelerate or decelerate. This is just gravity causing clocks to run slower and rulers to shrink.

Recalling the very famous second postulate of Special Relativity declared by Einstein (1905):

“The velocity c of light in vacuum is the same in all inertial frames of reference in all directions and depend neither on the velocity of the source nor on the velocity of the observer”

Einstein's theory of special relativity says that the speed of light in vacuum is always measured the same (at 299,792.458 km/s) however this is only true locally for systems that are inertial, which means not accelerating. From Newton's second law: if forces exist implies acceleration exists; this means that if you are in a spaceship and fire your rockets then you are not inertial.

The other factor besides acceleration is gravity. Albert Einstein himself emphasized in his paper in 1917:

“The results of the special relativity hold only so long as we are able to disregard the influence of gravitational fields on the phenomena”

In 1915 (10 years after Special Relativity) Einstein developed another theory called General Relativitythat deals with gravitational fields and according to this latest theory the velocity of light appears to vary with the intensity of the gravitational field. For example, an observer outside gravitational fields measures the speed of light locally (in his location) at 299792.458 km/s but when he looks towards a black hole he sees the speed of light there to be as slow as a few meters/sec. At the same time an observer freefallinginto that black hole (zero-g) measures the speed of light locally (in his location) at 299792.458 km/s; when he looks towards the black hole he sees the speed of light there much slower; when he looks away from the black hole he sees the speed of light there much faster. If he tries to resist his freefall into that black hole (by firing his rockets for example) he will not measure the speed of light locally anymore at 299792.458 km/s; instead the stronger the g-force that he feels the faster light appears to him. Again when he looks towards the black hole he sees the speed of light there much slower; when he looks away from the black hole he sees the speed of light there much faster. In any case, freefalling or not, he will never see the speed of light outside gravitational fields at 299792.458 km/s. Finally, there is no difference between the effects of g-forces experienced from these rockets and the effects of g-forces experienced when standing on planets, stars... hence an observer standing on a black hole measures the speed of light locally (in his location) much faster than 299792.458 km/s; when he looks towards outside gravitational fields he sees the speed of light there a zillion km/s.

In the presence of gravity the speed of light becomes relative. To see the steps how Einstein theorized that the measured speed of light in a gravitational field is actually not a constant but rather a variable depending upon the reference frame of the observer:

Mango Ice Cream - Indian Dessert Recipe Video

Worldwide Permaculture

Introduction

Permaculture is a design system based on ethics and design principleswhich can be used to establish, design, manage and improve all efforts made by individuals, households and communities towards a sustainable future. The permaculture flower uses the evolutionary spiral path to link together the key domains required for this change.

These concepts are adapted from Permaculture Principles & Pathways Beyond Sustainability by permaculture co-originator David Holmgren.

By adopting the permaculture approach we can make the transition into a world of less available energy, making our local communities more resilient to the converging issues of Peak Oil and Climate Change.

Permaculture Pioneers book launched

 

This book explores social and inner change for sustainability, charting a history of the first three decades of permaculture, through the personal stories of some of Australias most influential pioneers. From co-originator David Holmgren, to ABC TV's Gardening Australia presenter Josh Byrne, the authors span the generations and the continent.

The IPC10 in Jordan will bring together some of the world's most capable permaculture practitioners, teachers, visionaries and activists, enabling them to share their combined wealth of knowledge, experience and inspiration with the people of Jordan, each other, and the world at large. The result is expected to be increased efficiency at bringing permaculture's strong tendency to get to the heart of water, soil, energy and other global problems - by dealing with their root causes in holistic ways - to the people who need it most.

IPC10 will be held in Jordan across September of 2011.

Permaculture Song

Ever wondered what to say when someone asks you what permaculture is? Recent PDC graduate Dave Griswold has eloquently put it into song.

Animating the principle icons for a video clip could be a fun way to spread the word, anyone with the skills want to help put something together?

The Worldwide Permaculture Network beta is up

Craig Mackintosh from the Permaculture Research Institute has now launched the WPN which enables anyone to see at a glance some of what's going on around the world in permaculture.

With profiles of people and projects, along with locations the site is a fantastic tool for networking amongst the permaculture community.www.permacultureglobal.com

Late season discount now available! 

Featuring inspirational stories combined with beautiful photos the permaculture diary and calendar make the perfect ethical gifts.

Click on the images above to explore some of what is inside...

Permaculture Principles now in French

With thanks to the great work of Richard Wallner, Kristen Lagadec, Nicolas Salliou and Patricia Bourguignon at l'association Imagine Un Colibri we now have a French translation of the site.

The 12 permaculture design principles are thinking tools, that when used together, allow us to creatively re-design our environment and our behaviour in a world of less energy and resources. These principles are seen as universal, although the methods used to express them will vary greatly according to the place and situation. They are applicable to our personal, economic, social and political reorganisation as illustrated in the permaculture flower. The ethical foundation of permaculture (centre) guides the use of these design tools, ensuring that they are used in appropriate ways. Each principle can be thought of as a door that opens into whole systems thinking, providing a different perspective that can be understood at varying levels of depth and application. Read more about how design principles can be applied to business, by Rob Hopkins. Download a free poster of the principlesto spread the word.

A summary of the DVD about the principles can be viewed below:

Urban Permaculture

Farming With Nature - Permaculture with Sepp Holzer

Superhero

A Permaculture Food Forest

Permaculture Principles at Work

Bacteria cleans toxic water

THE UNIVERSITY OF NEW SOUTH WALES

The bacteria can destroy hazardous industrial toxins that arise from PVC plastic production. Image: LdF/iStockphoto UNSW researchers have shown that they can safely destroy hazardous industrial toxins in groundwater arising from PVC plastic production by injecting naturally occurring bacteria into a contaminated Sydney aquifer – an Australian first that raises hope of cleaning up this and similarly polluted sites around the country. The trial has confirmed the bacteria's natural ability to degrade and clean up chlorinated solvents that leaked many years ago from a former ICI Australia chemical plant into the Botany Sands Aquifer, creating large plumes of contaminated groundwater. ICI's successor, Orica Australia Pty Ltd, presently pumps out the contaminated water to prevent the plumes from spreading and entering Botany Bay. That water is then piped to a special treatment plant for decontamination. No other feasible option has been available. "With present technology, it was expected that it might take decades or perhaps centuries before these toxic solvents are removed from the aquifer," says Associate Professor Mike Manefield, who led the research team. "The energy demands and hence the financial burden of operating the contaminant containment system over this period of time is significant, but with our cultures in the ground we have the potential to greatly reduce the cleanup time and the cost and environmental footprint of containment.   "Our tests showed that these bacteria effectively breathe these pollutants the way we breathe oxygen.  It's a big step forward. These cultures represent a greener and cheaper tool we can use to clean up some of our contaminated sites.  They have not previously been available in Australia.  The real appeal is that they’re Aussie bugs." Associate Professor Mike Manefield is a Future Fellow in the UNSW School of Biotechnology and Biomolecular Sciences and Deputy Director of the Centre for Marine BioInnovation. "We're now very hopeful that other contaminated industrial sites, such as at Altona, in Victoria, can be cleaned up relatively quickly in this way as well," he says. The researchers collected bacteria occurring naturally in the Botany aquifer and isolated three bacterial communities that live off the breakdown of pollutants, including the first one known to degrade chloroform – a possible carcinogen that has been banned for many years in consumer products. It was found that bacteria had not degraded more of the pollutants on their own because they could not build up and sustain large populations in the aquifer due to a lack of food.  Further studies in which large volumes of the bacteria were grown in beer kegs showed that they thrived on a variety of diets, including ethanol, glucose and emulsified vegetable oils. Cost effective methods for distributing and sustaining the bacteria in contaminated soil and groundwater have been developed internationally and the Australian environmental consulting sector has the expertise and capacity to do the same on this continent. The next step will be to inject large numbers of the home-grown bacteria and a suitable food supply into polluted groundwater. The team will soon publish technical details of the discovery of these cultures and has received $1.14 million in funding from industry and the Australian Research Council to carry out a large-scale biological remediation of groundwater at Botany and Altona. "Cultures for chlorinated solvent degradation have not been available in Australia before owing to our strict quarantine laws, so this puts a new technology in the tool box of the remediation industry in Australia," says Associate Professor Manefield. "We've also devised new ways for the technology to have maximum impact when it is used”.

Vicious snails hunt crabs

THE UNIVERSITY OF QUEENSLAND

A voracious predator that devours prey larger than itself has been found lurking beneath Queensland's golden sandy beaches. Waves of scurrying blue soldier crabs are a common sight on the sand and mud flats of Moreton Bay near Brisbane and new research led by Dr Thomas Huelsken, from The University of Queensland's (UQ) School of Biological Sciences, has found these crabs have a good reason to stay on the move. Dr Huelsken has discovered the Australian endemic moon snail, Conuber sordidus, can surge up out of the sand to grab fast moving soldier crabs. Some of the crabs caught are larger than the attacking snail. Capturing this behavior on film for the first time, Dr Huelsken said the beautiful polished shells of moon snails belie their nature as vicious predators. “Moon snails are well known for attacking other snails and bivalves and until now, moon snails have been thought to feed almost exclusively on shelled molluscs,” Dr Huelsken said. “This observation that they also prey on crabs is a total surprise. Moon snails have now secured their status as top predators of the intertidal sand flats.” Dr Huelsken said the slow-moving moon snails typically creep up on other molluscs, and upon reaching their prey, drill through their victim's shell, eating them alive through the hole. “Many beaches have a littering of empty shells that have perfect round holes left by an attacking moon snail. These empty shells provide important clues for paleontologists who are studying how prehistoric molluscs interacted with each other and their environment,” Dr Huelsken said. “Moon snails were thought to exclusively eat other molluscs and have left clear evidence of their attack on the remaining shells. They have been important scientific models for understanding past predator-prey interactions. “Now, we can surmise that paleo moon snails were probably eating crabs too, but have somehow not left a fossil record for that part of their diet.” “This means that the fossil record of moon snail predation may not be as complete as previously believed.”

Shallow ponds cut water loss

FLINDERS UNIVERSITY

Research by Flinders University’s School of the Environment has shown that a shallow, high-rate pond system to treat wastewater will slash the loss to evaporation as well as boosting the rates of removal of bacterial and viral pathogens. The research results will be presented at the International Water Association’s conference on Wastewater Stabilisation Ponds, which will be hosted by Flinders from August 1 to 3, 2011 at the Stamford Grand Hotel at Glenelg. PhD researcher Mr Neil Buchanan (pictured)  said that at present evaporation from treatment ponds wipes out a large proportion – up to 90 per cent – of reclaimed water in South Australia’s small rural communities, where there is strong unmet demand for clean and relatively cheap water. The research project compared a high-rate algal pond at Kingston-on-Murray with a conventional treatment pond system at Lyndoch. Funding for the performance research comes from the SA Local Government Association, which is assessing the viability of advanced pond systems for use in rural areas. Mr Buchanan said that the depth and relatively static nature of conventional waste stabilisation ponds means that the combined decontaminating effect of sunlight and algal activity is limited to an upper layer of about eight to 20 centimetres. The high rate algal pond, by contrast, uses a slowly revolving paddle wheel to aerate and move the water through a shallow, winding course. Moving the water exposes viral and bacterial pathogens to the direct effect of ultra-violet light while also inducing stronger algal growth. “The chemical effect of the algae is to increase levels of alkalinity in the water, which acts as a strong disinfectant,” Mr Buchanan said. The result, compared to a conventional pond system, is reduced evaporation and a higher rate of pathogen removal. “The high rate pond has a surface area of about one fifth of the pond system, and our work to date suggests that in a fifth of the area we are getting the equivalent of double the rate of the removal of pathogens,” Mr Buchanan said. “So overall, you could say that we could reduce the surface area and the evaporative losses by a factor of ten.” While Australian reuse applications require an emphasis on pathogen removal, in Europe the foremost consideration is reducing nutrient load, since wastewater is often discharged into waterways. “So concurrent with the pathogen work, we are also studying the rate of removal of nutrients from the water,” Mr Buchanan said.

Lalitha Sahasranamam Full (Stotra & Meaning)

A Quick, Cheap Diagnostic Test for HIV and Other Infections

BIOMEDICINE

A simple microfluidics chip could improve health care in poor countries by making rapid diagnostic testing a reality.

• BY EMILY SINGER

Audio »

A small plastic chip that costs just 10 cents to make can reliably diagnose HIV and syphilis within about 15 minutes. The chip, which is based on microfluidics, uses small wafers that precisely manipulate nanoliter volumes of fluid in order to carry out a sequence of chemical reactions.

Developed by Samual Sia and collaborators at Columbia University, the system was designed to be used in resource-poor settings. Field tests in Rwanda showed that the chip works as well as traditional laboratory-based HIV diagnostics. Sia wants to deploy the test in prenatal clinics in Africa.

Many health clinics and even city hospitals in Africa must send out blood samples to a national laboratory for processing—a process that can take days or weeks. But in poor, rural areas, where patients may have to travel days to reach a clinic, many people are unlikely to return for a second visit to get their results. Tests that give reliable results in minutes could make a huge difference by letting the physician treat the patient during the visit.

While rapid diagnostic tests for HIV and some other infections already exist, they are typically not used in poor areas of Africa because they are more complicated to read and more expensive to use. Such tests are limited to detecting a single disease per use. With Sia's chip, additional tests, such as for hepatitis or malaria, can be added to the chip without increasing the cost significantly.

To make microfluidics technology more practical to use in poor countries, Sia's team designed it to be inexpensive to make and easy to read, and then tailored manufacturing methods for those purposes. The chips are produced via a plastic injection molding process that has been optimized to create nanoscale features. The reagents for the detection reaction are stored in a tube, separated by bubbles of air, and brought into the chip with the simple pull of a syringe.

The process requires no moving parts, electricity, or external instrumentation, and it requires a very small amount of blood—about one microliter. Unlike many microfluidics devices, the results can be read without microscopes or other expensive optical systems. A simple optical sensor on an instrument that's about the size and cost of a cell phone gives the test results.

Sia's team worked with Columbia's School of Public Health, the Rwandan administrator of health, and nongovernmental health organizations to test the device in Rwanda's capital city of Kigali. As many as 8 percent of women in Kigali are HIV positive, and it can take days or weeks to get the results for HIV tests at the hospital because blood samples must be sent to an outside lab for analysis. When Sia's device was used to test for HIV, and HIV and syphilis in combination, it detected 100 percent of cases, with a false positive rate of about 4 to 6 percent—on par with standard laboratory tests. The findings were published today in the journal Nature Medicine.

Recognizing the challenge of raising funds to commercialize a technology for poor nations, Sia and two partners founded a company called Claros Diagnostics. They won venture funding to develop a device for use in doctors' offices in wealthy countries to monitor signs of prostate cancer—a device that garnered marketing approval in Europe in June. Sia's team at Columbia then adapted the technology to test for sexually transmitted diseases; in addition to HIV and syphilis and hepatitis, they are working on tests for hepatitis B and C, herpes, and malaria. While the test was developed for use in poor countries, it might ultimately find appeal elsewhere as well.

Sia's initial focus is on prenatal clinics. "If you catch the diseases in mothers, you can prevent transmission to newborn, increasing clinical impact," says Sia. According to the research, syphilis testing in mothers and pregnant women could reduce the number of years lost due to ill health, disability, or early death by 200,000 in Rwanda.

Sia and his collaborators still face a major hurdle: finding funding to develop the STD device into a commercial product. While the researchers won grants and garnered venture-capital funding to develop the technology, including money from the Gates Foundation to find the best market, they have yet to secure funds to widely implement the technology. Ironically, the Gates Foundation declined to fund the next step in development, though research showed that STD testing was the optimal market to apply the technology.

Nanofiber Regenerates Blood Vessels

Capillary action: The transparent circle in the center of this image is a nanomaterial designed to mimic the protein VEGF. Here, it has enhanced the growth of blood vessels in the membrane from a chicken egg after three days.
Credit: Matthew Webber

BIOMEDICINE

A synthetic material may help to repair tissue after a heart attack, and aid transplants.

• BY KENRICK VEZINA

Audio »

Regenerating blood vessels is important for combating the aftereffects of a heart attack or peripheral arterial disease, and for ensuring that transplanted organs receive a sufficient supply of blood. Now researchers at Northwestern University have created a nanomaterial that could help the body to grow new blood vessels.

Samuel Stupp and his colleagues developed a liquid that, when injected into patients, forms a matrix of loosely tangled nanofibers. Each of these fibers is covered in microscopic protuberances that mimic vascular endothelial growth factor, or VEGF—a protein that occurs naturally in the body and causes chemical reactions that result in the growth of new blood vessels. By mimicking VEGF, the nanofiber has the same biological effect.

Jeff Karp, director of the Laboratory for Advanced Biomaterials and Stem-Cell-Based Therapeutics at Brigham & Women's Hospital, says, "this is an elegant approach to rationally design engineered materials to stimulate specific biological pathways." Karp was not involved with the project.

Ali Khademhosseini, an associate professor at the Harvard-MIT Division of Health Sciences and Technology, adds that "the ability to induce blood vessel formation is one of the major problems in tissue engineering."

Tissue engineers have tried using VEGF itself to stimulate the growth of blood vessels, but clinical trials with the protein were unsuccessful, says Stupp, director of the Institute for BioNanotechnology in Medicine at Northwestern. This is because VEGF tends to diffuse out of the target tissue before it can do its job. Maintaining a therapeutic concentration in the target tissue would require a series of expensive, invasive injections.

The new nanomaterial has a similar effect, but it lasts much longer, and is completely biodegradable once its job is finished. Stem cells could be used to regenerate blood vessels, but their use is expensive and controversial.

The researchers tested their material in mice. The blood supply to the animals' hind legs was restricted. Left untreated, these limbs would die. The nanofiber treatment rescued the limbs, and resulted in better motor function and blood circulation than the other treatments, including a treatment with VEGF.

Stupp says there could be more uses for nanofibers that mimic proteins from the body. For example, they could be used to stimulate the formation of connective tissues such as bone and cartilage, or to regenerate neurons in the brain.

"The next step is to proceed with extensive toxicological testing," says Stupp. "The long view would be to produce a cell-free, growth factor-free therapy for the treatment of ischemic disease and heart attacks."

Khademhosseini also sees a lot of potential in nanomaterials that mimic natural proteins. "Such materials could have a great future application in regenerative medicine, as they will enable the body's own regenerative response to heal," he says.

World Bank & Civil Society - A Renewed Engagement

India: Self Help Groups