A vacuum is a space that has less gaseous pressure than the standard atmospheric pressure at sea level on Earth. A partial vacuum can be easily created by simply pumping air out of a container. If the container is not sealed, though, the air will be replaced fairly quickly.
In everyday life, vacuums are used in light bulbs, cathode ray tubes, cleaning appliances, and to package, protect and preserve a range of foodstuffs. Creating a vacuum drove the piston mechanism in the Newcomen steam engine and was also used in the braking systems of trains. Household vacuum cleaners work by sucking in air, which creates a lower air pressure than that outside the device. To restore the partial vacuum the outside pressure forces air, and with it dirt/dust etc, into the appliance.
The purest vacuums can be found in outer space Between galaxies, the vacuum density drops to -0.001 atoms per cubic centimetre, while in the void between stars in the Milky Way, the vacuum is -0.1-1 atoms per cubic centimetre. This is in contrast to a vacuum cleaner that produces a vacuum of around 1019 molecules per cubic centimetre, though highly sophisticated extreme-high vacuum (also known as XHV) lab chambers have managed to achieve a vacuum of fewer than 1,000 molecules per cubic centimetre.
Whether man-made or natural, there is no such thing as a perfect vacuum. Even in a virtually complete vacuum, physicists have discovered the presence of quantum fluctuations and vacuum energy. See opposite for more on fire and sound work inside a vacuum.
Solar tsunamis are surges of material sent crashing across the Sun as the result of a solar flare being launched into space. They can travel at speeds up to 1.6 million km (1 million miles) per hour. These solar tsunamis are made of hot plasma and magnetic energy.
The first was observed by Gail Moreton in 1959, and since then several more studies have been conducted by the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) spacecraft, both of which orbit the Earth.
Solar tsunamis are formed when the Sun emits a coronal mass ejection (CME) – a massive burst of solar wind commonly associated with solar flares. Around the ejection point, a circular wave extends outwards in all directions and travels across the surface of the Sun at a super-fast rate. In February 2009, the two STEREO spacecraft watched as a billion-ton cloud of gas was hurled off the surface of the Sun from a CME.
The result of this ejection was a massive solar tsunami that towered 100,000km (60,000 miles) high and which sped across the star’s surface at about 900,000km (560,000 miles) per hour. It was estimated to contain the same energy as 2.4 million megatons of TNT.
Solar wind streams from the Sun at a blistering 400 kilometres (250 miles) per second. The intense heat of the corona – the outermost portion of the Sun’s atmosphere – energises particles to such a level that the Sun’s gravitational field can no longer hold on to them and they escape into space.
Solar wind strength varies, creating space weather capable of disrupting technology, like global positioning system (GPS) satellites.
The movement of solar wind has a characteristic pattern that resembles a rope wobbling up and down – technically known as an Alfvén wave (after Hannes Alfvén). These magnetic strings can be observed as the greenish light that appears during the polar auroras.
Until recently scientists have struggled to understand this unusual wave behaviour, but a new set of models – based on similar waves generated by polarised light – might enable us to understand, and even predict, future fluctuations in solar wind.
Sweat is produced by dedicated sweat glands, and is a mechanism used primarily by the body to reduce its internal temperature. There are two types of sweat gland in the human body, the eccrine gland and the apocrine gland. The former regulates body temperature, and is the primary source of excreted sweat, with the latter only secreting under emotional stresses, rather than those involved with body dehydration.
Eccrine sweat glands are controlled by the sympathetic nervous system and, when the internal temperature of the body rises, secrete a salty, water-based substance to the skin’s surface. This liquid then cools the skin and the body through evaporation, storing and then transferring excess heat into the atmosphere.
Both the eccrine and apocrine sweat glands only appear in mammals and, if active over the majority of the animal’s body, act as the primary thermoregulatory device. Certain mammals only have eccrine glands in specific areas – such as paws and lips – warranting the need to pant to control their temperature.
Most touchscreens use capacitive sensing, which uses two glass layers, coated on their inside surfaces with strips of a transparent conducting material called Indium Tin Oxide.
On one layer the stripes run horizontally and on the other layer they run vertically. Each intersection acts as a tiny capacitor that stores an electric charge. When your finger touches the glass, it distorts the electric field and changes the amount of charge the capacitors underneath it can hold.
The red colour that we usually see in images of Mars is actually the result of iron rusting. Rocks and soil on the surface of Mars contained a dust composed mostly of iron and small amounts of other elements such as chlorine and sulphur. The rocks and soil were then eroded by wind and the resulting dust was blown across the planet’s surface by the activity of ancient volcanoes. Recent evidence suggests dust was also spread across Mars by water, a theory backed up by the presence of channels and ducts across the planet’s surface.
The iron contained within the dust then reacted with the oxygen in the atmosphere, producing the distinctive red rust colour, while the sky appears red because storms carried the red dust high up into the planet’s atmosphere. This dusty surface, which is between a few millimetres and two metres deep, also sits above a layer of hardened lava which is mostly composed of basalt. The concentration of iron that is found in this basalt is much higher than it is in basalt on Earth, and this also contributes to the red appearance of Mars.
When we breathe in, the inhaled air can contain dust, chemicals and other irritants that can be harmful to the body, particularly to organs in the respiratory system like the lungs. While the tiny hairs inside the nostrils (cilia) trap many of these particles, some will often get through. To help you out, your body reacts to try and forcibly expel the offending particles via the sneeze reflex arc.
There are a number of other reasons why we sneeze, including to clear the nasal passages when you have a cold, to expel allergens if you are allergic to something, and even bright sunlight can cause some people to sneeze.
When a stimuli is detected by the nerve endings in the nose, impulses are sent to the brain, which initiates a chain of physiological events that enable the body to rid itself of the unwelcome item.
Barcodes are a machine-readable way of writing letters and numbers. A laser is shone onto the barcode and the reflected light can be interpreted by the barcode reader. There are many types of barcodes, but the ones most commonly found in supermarkets use a row of lines of different widths.
The different widths represent different numbers. In the UK many items are coded with a GTIN – Global Trade Item Number. This allows the manufacturer to print the barcode on the packages. The numbers are unique to that item. The barcode only has a number, but no product information.
That is held in a database which the retailer can access at the point of sale. It also means that shops can set their own prices and change them easily.
Calories measure energy and can be used to describe any fuel from petrol to bread. One calorie is the amount of energy required to raise the temperature of one gram (0.035 ounces) of water by one degree Celsius (1.8 degrees Fahrenheit). Food labels often quote energy content in kilocalories (kcal), because food is so rich in energy that it makes more sense to label 1,000 calories at a time.
The number of calories in any given item of food is calculated by measuring how much energy is released when a substance is burned. Inside our bodies, molecular machinery is responsible for burning the fuel we eat, but in the lab, using a spark gives the same result. The traditional method of calorie calculation is to put the food inside a sealed unit known as a bomb calorimeter.
The food is surrounded by an atmosphere of oxygen to ensure it will burn well, and the container is sealed and surrounded by a known volume of water. A spark ignites the food inside and allows it to burn until it is reduced to charcoal, releasing all of the energy contained inside.
The energy is converted to heat, which in turn raises the temperature of the water. By measuring the water’s temperature change, you can then find out exactly how much energy has been released and calculate the calories from there.
Today, many food manufacturers use a different system to create nutritional labels; instead of burning the food item whole, they simply add up the calories of the different components, such as fats, carbohydrates and proteins.