My Science School

  A stainless steel femur rod does not set off airport metal detectors because it is made of non-magnetic stainless steel.

            Stainless steel is made in two forms: austenitic and ferritic. Austenitic stainless steel is nonmagnetic. It is the common form used in cooking pots and for surgical hardware.

            Ferritic stainless steel is magnetic. It is used in some knives and guns and for various industrial purposes.

            Non-stainless steel (carbon steel) is magnetic. It is used in most knives and guns.

            Metal detectors do not detect metals as such; they detect the distortion of a magnetic field produced by materials of high permeability.

            Magnetic materials have high permeabilites which greatly distort the field and so are ready to detect.

            Nonmagnetic materials have low permeabilites and as a result have little effect on the field and are difficult, if not impossible, to detect.

            The small bunch of keys detected at the airport is probably on a magnetic steel ring because most keys are made of nonmagnetic metals, such as brass or aluminum.

            One can avoid setting off airport metal detectors by limiting the number of bank credit cards (they have magnetic stripes) and by touching all the metal things with a strong magnet and not carrying those it attracts.

Generally tyres of vehicles are filled with air to absorb the shocks generated as the vehicle moves on uneven roads, and make the ride comfortable.

The shock absorbing capacity is enabled by a fundamental property of air namely compressibility - air gets easily compressed to smaller volumes on application of pressure.

But water is not compressible and so if one uses it to fill the tyres, all the shocks generated on the tyres will be completely passed on to the vehicle and its passengers will feel the discomfort.

In addition water-filled tyres increase the rolling resistance of vehicles because of the increase in weight. Hence apart of the engine’s power and fuel is wasted in overcoming this resistance.

Tubeless tyres are not popular in India because of two reasons. First, rusting of rims, which leads to air leak, is a perennial problem in the tropical climate. Second, fitment of such tyres needs special tools and presses and so they cannot be repaired in road-side shops. In conventional tubed tyres, load is carried by a volume of air held inside a tube which is closeted to the inside of the rim at the bottom and to a tyre over the remaining area. In tubeless tyres, the type itself holds the air. Outwardly, a tubeless tyre resembles a tube tyre. The inside of a tubeless tyre has an airtight lining extending the beneath the bead (the part of the tyre that anchors it to the rim) when inflated. In order to provide perfect sealing, a special coat of rubber is provided to the inside wall of the tyre which is fitted to the rim using rubber seals. The special bead seating (on the rim) also prevents air leak. There is no need for a flap and so a value is fitted to the rim itself for inflating or deflating the tyre.

 Tubeless tyres have distinct advantages over conventional tubed tyres. For example, down time is reduced due to the elimination of tube and flap troubles, and fitting is easier. It gives cooler running - which is important in high ambient temperatures and on long hauls.

Unnoticed accidental damage can lead to a burst with tubed tyres. (The air escapes through the tube-tyre interspace). Such damage shows up as a slow leak in tubeless tyres. There is no run-flat situation and so the user can safely travel up to 10-15 km before setting it right. These obvious advantages of tubeless tyres have led to its adoption in many other countries. 

Automotive tyre consists of a number of rubberized fabric layers and the layer is called ply. A collection of such plys is called carcass or casing. It is this casing which is responsible for the tyre’s performance including its load bearing capacity.

Originally cotton tyre fabric was used. Irrespective of the nature of the fabric nylon/rayon/polyester), the strength of the carcass is equated to the number of ply. This convention is still followed in cross-ply tyres.

 For example, the 8 ply-rating of nylon fabric reinforcement implies that the strength of the carcass is at least equal to 8 cotton plies. But the actual number of nylon fabric ply could be 4 or 6 (because nylon is much stronger that of cotton). But this numbering system is beset with two misconceptions: One is that the tyre consists of that many of plys and the other one is that the strength of the carcass is limited to the number of plys. 

To overcome this, nowadays, the ply rating is also indicated in alphabetical letters. 

Ply rating of tyres is the number of layers of soft rubber-clad fabric below the tread (rubber layer) of a tyre. The fabric nylon or rayon is subjected to tension before calendaring. The tensioned fabric is then rolled between steel rolls with rubber on top and bottom of the fabric. The calendar is then cut at 45 degrees according to the width of the tyre to be manufactured. The cut calendar is placed on the drum with rims on both sides of the drum to make a skeleton of the tyre. The tread (rubber) is placed on the skeleton and pressure is applied to stick the tread-to the calendar. Later on it is cured and moulded to actual shape. 

       Ordinary tyres or cross-ply tyers are the oldest type of tyre and has a case made of two or more layers of fabric. A tyre’s strength and load carrying ability were at one time indicated by its number of piles. Modern materials and manmade fibres such as polyester and glass fibre embedded in the rubber are much stronger than the cotton fibres originally used.

            Radial tyres give the impression that they have low inflation even though the air pressure is as recommended by the manufacturer. This is primarily because of the soft sidewalls. The physical difference between the radial and cross-ply tyres and in their behaviour on the road is governed by the difference in their individual carcass construction.

            Carcass is the rubber-bonded cord structure of a tyre integral with the bead and contains the inflation pressure. The radial ply has a stiffness and resistance in its tread area, so that in motion the tread in the contact patch retains virtually all of its pattern and grip.

            Radial tyres normally give twice as much mileage as cross-ply tyres and the difference in cost is not more than 30 percent sometimes even less and gives a marginally harder ride but is safer at high speed.

            Radials make the steering a little harder than cross-ply tyres, but provide better braking performance. The carcass of cross-ply tyres consist of textile cord ply fabric, but in a radial tyres it consists of steel belted cord laid substantially 90 {+0} to the centre line of the tread.

            Tyre consists of layers of cord called ‘plies’. Plies are shaped on a form and impregnated with rubber. There are two ways to apply the plies on the bias and radially.

                In bias type (ordinary) tyres the plies are criss-crossed. One layer run diagonally one way and the other layer runs diagonally the other way. The arrangement makes a carcass that is strong in all directions because of the overlapping plies. However the plies tend to move against each other.

            This movement generates heat, especially at high speed. Also the tread tends to ‘squirm’ or close-up as it meets the road. This increase tyre wears. Tyres with radial plies were introduced to remedy these problems.

            In radial tyres, all the plies run parallel to each other and are vertical to the tyre bead. Belts are applied on top of the plies to provide added strength paralleled to the bead. The radial tyre gives better fuel economy and lesser tyre wear.

        The source of the smell is most probably caused by bacteria and fungi feeding on organic matter in the rubbish. It will be more noticeable if the bin is in a warm and damp place.

            The smell will not always be exactly the same, but it will be more characteristic of the different organism than on the type of food they consume.

            The smell one gets from penicillin mould growing on an orange will be exactly the same as that from penicillin mould grown in a laboratory culture. It is pungent, characteristic and very common.

            Analyses of household rubbish have detected pathogenic bacteria, including Pasterurella pestis, the bacterium responsible for causing bubonic plague. So do not sniff too hard.

The Babylonians 3000 years ago used the sexagesimal system of numbering, which was based upon a multiplication of 6, instead of the decimal system which we now use. They divided the circle for example into 60x6 parts - the 360 degrees. Each degree in turn was divided into 60 parts was again divided into 60.

Claudius Ptolemy took this method of division from the Babylonians and called the first division of the degree the parts minutiae, or a small part. The division of this first small part he called the ‘pars minutiae secundae’ or the second small part, Ptolemy’s names became known as minutes and seconds.

Extracted from the book by title ‘Tick Tock’ compiled by I. Step nova, Prosveshcheniye Publishers, Moscow 1981, Page 36.The Babylonians calculated the number of days in a year as 360.

 The earth moved through the Zodiac in 360days as per their estimate and hence the division of the circle into 360 degrees, that is one degree per day. Time measurement is also based upon the sexagesimal system as there are 60 seconds to a minute, sixty minutes to an hour, 24 hours to a day, 30 days to a month and 12 months to an year and also 12 Zodiacal signs in astronomy.

The frequently used angular measurements in Geometry – 30’, 60’, 90’, 180’, & 360' are all multiples of six. The Gradian measure of dividing the quarter of a circle into 100 parts has not become popular. The angular and time measurements remain sexagesimal to this day even though the other two viz. Length and mass of the fundamental measurements have been metricated long back.

    Linear editing systems and non-linear editing systems are used in video and film editing. In Linear editing systems, edits to be made in a linear fashion, i.e. in 1-2-3 sequence.

One or more tapes containing the original footage are transferred (recorded) segment by segment onto a tape in a video recorder. In this process, the original segments can be shortened and rearranged, bad shots can be removed, and audio and video effects can be added.

 The source machine(s) contain the original footage and the edit recorder, which is controlled by an edit controller, is used to record the final edited master.

The person editing, using an edit controller to shuttle tapes back and forth to find the beginning and ending points of each needed segment. These reference points are then entered as either control track marks or time code numbers. The editor then turn things over to the edit controller, which uses the precise beginning and ending points that have been entered, to roll and cue the tapes and make each edit.

 Non-linear editing is a little like working with a highly sophisticated word processor; it allows segments to be inserted, deleted and moved around at any point in the editing process. In non-linear editing the original video segments are digitized (they are not in digital form when they come out of the camera) and transferred to computer hard disks. The editing system can access them in any order, almost instantly.

During nonlinear editing, a wide range of special effects can be added, including fades, dissolves, keyed in words and scene to scene colour corrections. Many audio enhancements can also be added, including sound effects.

Tear gas is a noxious gas. It is also called as war gas since it is used to disperse soldiers in a battle and all attacking mob. It is one kind of Lachrymator. Firing certain chemicals in artilleries or pen gun produces it. The chemical substance used is, alpha chloracetatophenone, a solid material or ethyliodoacetate a liquid material.

 The tear gas vapours cause irritation of the eyes with a copious flow of tears, spasm of the eye lids and temporary blindness. When eye is exposed to this irritant gas it creates a nervous reflex caused due to sensory stimulation.

As a result of this stimulation tear gland is induced to secrete copious tears, which flush across the eyeball. Tear gas also causes irritation of air-passages. In long continuous exposure there may be nausea, vomiting and blistering of skin. The effects are transitory.

Tear gas exposed persons should be removed to fresh air and they should wash their eyes with normal saline or boric acid solution. Weak sodium bicarbonate solution should be applied to the affected parts of the skin.

Intensity of the harmful radiations coming out of TV screen is strong near it and gradually falls In simple terms, the eye consists of a cornea (in the front), eye lens (in the middle) and retina (at the back). The space between the cornea and the eye lens is filled with an aqueous humour and that between the lens and retina is filled with a vitreous humour. Ciliary muscles hold the eye lens in its place and also change the shape (curvature) of the lens (to adjust the focus on objects) along with the help of the fluids.

 If one sits too close to the television or cinema screen, the eye Lens has to do more frequent focusing for viewing. Light rays from a near portion of the picture diverge and so the lens is curved more to focus on them. Simultaneously, the lens has to collect the light (coming more parallel) from more distant parts of the picture. This causes strain on the eye, and if practiced for long, can permanently damage the eye.

In addition, for optimum resolution of the picture and to reduce the level of radiation from the TV screen, we are advised to sit at a distance while watching the programmers.

In fact, the limit of resolution of the human eye is 1 mm at a distance of about 3 m. If one watches a TV sitting close to it one can see the picture elements (grains) which make up the picture. To see a clear sharp picture without eye strain, one must sit at an optimum distance so that the individual grains merge to form a complete picture.

 In a typical case, the main field of vision of the eye is defined by the vertical and horizontal viewing of 30-40 degrees; beyond which the vision is poor. Therefore, for comfortable viewing, a viewing angle of 10-15 degrees at the eye is optimum.

The width-to-weight ratio of the TV screen is kept as 4:3 because of the binocular vision due to the pair of eyes in the horizontal plane and the range of movement of both the eyeballs being less restricted in the horizontal plane as compared to that in the vertical plane. Hence, the best viewing distance for watching TV is 4-8 times the height of the screen (for a visual angle of about 10 degrees). For 51-cm TV, the minimum viewing distance should be 2.5 m. this minimum distance reduces eye fatigue by avoiding rapid movement of the eyeballs.

Also the light that falls on the eyeball comes directly out of the TV screen. Hence the with the distance from the screen.

So, to reduce exposure to these radiations, it is better to sit a bit far away. (In a theatre, the light falling on the eye is actually those reflected by the wall/screen and so the harmful effects are less.)

To reduce the strain on the eye, there must be some light in the hall. And this should be placed preferably above or on the sides of the TV to avoid any glare from the screen. 

The cordless phone is an FM transmitter/receiver. The frequency range lies between 26.6 and 49.8 MHz A cordless phone essentially converts the audio signals from the telephone line into the FM waves and it is detected by the mobile handset, and vice versa. For security reasons the range is limited to about 100 metres and their power is about 500 milliwatts. Each cordless phone is assigned a particular channel (or frequency range) to avoid interference with nearby instruments. 

Cordless phone is based on wireless transmission and frequency modulation. The main components of a cordless phone are the base unit and the portable unit. While the base unit is kept at a fixed point, connected to power supply and the working telephone line, the portable unit can be carried to a certain distance, depending on the frequency range limitation. Normally in India, the permissible distance is about 100 metres.

 The base unit and the portable unit essentially consist of radio wave transmission and reception devices which enable a two way wireless communication between these units.

The radio waves are broadcast in the air through the antenna fitted to the units. Just like the signals emanating from the telephone are converted to radio frequency in the transmission side, the reverse happens in the receiver side, (i.e.) the radio frequency signals are converted into original signals, bell or speech.

 Since the handset does not have and connecting cord or wire, the name cordless phone.

            

    In normal telephone exchange systems, a pair of wires extends each telephone instrument to the telephone exchange.

Normally, copper conductors are used to give loop to indicate the exchange that the telephone hand set had been lifted for making a call or for receiving a call. In advanced countries, Optical Fibre is also used or for extending the loop.

When you make a call to your friend who is connected to another exchange, the digits are sent to the exchange to which you are connected, in the form of pulses (break and make of loop) or frequencies.

The originating exchange analyses these digits and establishes a path to the terminating exchange where your friend is connected. Over this path, signals (some of the digits dialed by you and other technical information) are sent in the form of bits or frequencies. 

The terminating exchange analyses and marks your friend's line and if it is free, a ring is sent to him and ring back tone is sent to you. When the call is answered, metering takes place.

In the cell phone system, there is no permanent wire connection between the instrument and the mobile telephone exchange. The connection between the instrument and mobile exchange is established via an intermediate station called Base Station (BS) where a transmitting tower is erected. The connectivity between the mobile exchange and the BS may be wire and between BS and Cell Phone is a Radio Channel.

The connection between a mobile exchange and another mobile exchange or public telephone exchange is by wire.

 Cell phones are technically called Mobile Station (MS) and its telephone exchange is called Mobile Switching Centre (MSC). The radio channel for both-way voice and control channel for controlling are established between BS and MS whenever required only.                                

A town or an area is divided into smaller areas called Cells. At the centre of the cell, there exists the Base Station (BS). When the MS moves around inside the cell, the signals including voice will be strong. When you use a cell phone to talk to your friend with conventional phone, you will   be connected to the BS over a booth-way Radio channel. From BS to MSC over a copper cable or Optic Fibre cable, from MSC to another Exchange and further to your friend over a copper cable

            As you are moving and when you enter into another cell, old BS reports to MSC that you have left the cell and your signals are weak. Immediately, the MSC orders all other Base stations to search for a new comer (as far as other cells are concerned, you are a new comer).

 The BS which is very near to you reports to the MSC that it has found a new corner with strong signals. The MSC orders the old BS to hand off (you) to new BS. Handing off is done in less than 400 milliseconds. But you do not feel any disturbance in your conversation. You may cross many cells during your long conversation without knowing that so many hands off have taken place. Each cell phone is associated with a unique identity stored in Subscriber Identity Module (SIM). This identity is sent to MSC through Base Station when ‘Send’ button is pressed.

The MSC analyses this and validates as to whether cell phone is authorized to make a call. If yes, the call will be put through. When there is an incoming call to the MS, first it is received by the MSC. MSC analyses the received information that contains the MS number also. This number is paged in all cells. If the MS is kept powered on, a page response is received on the control channel from the MS. A voice channel is allotted by MSC. BS and MS are ordered to tune to that channel. Once tuned through connection information is returned to the caller who gets ring-back tone. Ringing is initiated in the MS. When the MS answers, conversation can start and metering starts in MSC.

         Earth rotates from west to east causing the Sun, the Moon, stars and other planets rise from east and set in the west. On the surface of the earth each point is moving eastward with respect to an astronaut in space.

            Thus if a rocket is launched at a small angle eastward vertically the speed of earth gets added to the rocket’s speed. This reduces the amount of fuel required. If the rocket is inclined along any other direction, the speed of the earth gets subtracted from the speed of rocket and will necessitate burning of more fuel.

            In addition, in case of any failure during launch the rocket will fall back to the earth. Hence if it is launched from the east coast, the rocket will fall into the sea only. If it is launched from the west coast, in case of failure, the rocket will fall on the land endangering human habitats. Thus choosing eastward inclination is scientific but choice of eastern coast concerns safety.

            A small amount of air is trapped and pressurized when the fixed end of the thumb and the free end of the middle finger are brought together. When this pressurized air is released suddenly during the clicking it produces a sound as in the case of a balloon burst.

Sound is caused by the cracking of knuckles when a bubble which has formed in the lubricating fluid (the synovial fluid) which surrounds the two bones of the knuckles bursts.

Normally there is a lubricating fluid which prevents the two bones which forms the knuckles from grating against each other. This fluid contains tiny bubbles which cannot be seen by the naked eye.

So when the knuckle bones remain close together the fluid is under pressure and the bubbles remain tiny.

But when one clenches his fist, the bones are pulled apart which causes the bubbles to join together to form one large bubble. Then when one works the fist, the pressure changes and makes the bubble to burst which then produces a loud cracking, noise. Doctors are not sure whether cracking them is harmful or not, though there is a belief that cracking ones knuckles could make them large and unsightly.