Ballpoint pens have a tiny ball made of brass, steel or tungsten carbide as their writing tip. The ball is fitted into a socket and is connected to the ink reservoir by a thin tube. When we write on paper, the ball rolls due to friction between the ball and the paper. This rotating movement allows the thick ink to flow out slowly leaving a mark on the paper.
When drawn over a smooth surface such as glass or plastic there is little friction between the ball and the surface. The ball is unable to rotate and, as a result, the ink cannot flow out. Hence we cannot write on smooth surfaces with a ballpoint pen.
Spectacles are made up of lenses and are used to improve vision. For nearsightedness, concave lenses are used and for farsightedness convex lenses are used to give clear images. A microscope is an instrument which gives enlarged view of small objects. In an optical microscope, the objective makes a real image of the object which is further magnified by the eyepiece for the eye to see a magnified virtual image. The distance at which the magnified virtual image is formed can be adjusted by moving the eyepiece to suit the power of the spectacles one uses. So, one need not use spectacles while using a microscope in order to see the magnified image clearly. Besides, wearing spectacles also draws the eye of the observer away from the eyepiece thus reducing the field of view.
The pitch, loudness, duration and timbre are the four qualities which define the structure of a piece of music. The pitch or the high-low aspect of the sound is considered to be the most important unit in structuring music. The timbre or the ‘tone colour’ is the sum total of the simultaneous motions produced by any vibrating medium. This is unique for each instrument. The timbre also defines the fineness of the sound produced by an instrument. Differences in timbre of sound produced by different instruments are responsible for the different musical qualities of the various instruments. Thus musical notes produced by different instruments sound different inspite of the pitch being the same.
When we try to break a stick by bending it we use lever of the first kind in which the fulcrum lies between the load points, in this case, right below the point where the stick breaks. Since the force generated at the break point depends on the length of the lever arm, which in this case is the distance from the break point to the stick end, a longer stick is easier to break as it needs less effort compared to that needed to break a short stick.
Natural rubber is made up of long chains of the molecule isoprene with a few cross links between the chains. These kinked, looping polymers are intertwined in un-stretched rubber. When these polymers are subjected to a stretching force, the tangled polymer opens up because of the flexible bonds between the molecules and becomes elongated. When the applied force is released, the chemical bonds in the chains try to come back to their original state. This accounts for rubber’s elasticity.
When an electrical switch is operated it produces a spark at the contact point. This spark emits electromagnetic radiation. Since radio and TV signals are also electromagnetic in nature, the bursts of electromagnetic radiation produced by a spark is also received by the radio or TV set. This produces the disturbance which is heard as crackling sounds on the radio and snowy lines on the TV picture.
One of the laws of fusion is that the melting point of substances which expand on freezing is lowered by the increase of pressure, while it is raised in the case of those which contract on solidification. Ice belongs to the first category of substances, that is, it expands on freezing. Ice has an open structure which collapses when subjected to pressure, producing water which occupies lesser volume. That is why ice melts when subjected to pressure.
In filament lamps a good part of the electrical energy is used up in heating the filament which in turn glows throwing light around. While in fluorescent tubes light is produced by electrical discharge in a glass tube, the inside of which is coated with a fluorescent material. The filaments at the two ends are used only to start the discharge. The discharge passing through vapours of mercury produce UV radiations which excites the fluorescent coating producing visible light. Since very little heating is involved in the process and most of the electrical energy is used in producing light, fluorescent tubes consume less power than filament lamps.
A petrol engine can’t be run with diesel or a diesel engine run with petrol because the engines and their fuels are made for each other. In a petrol engine, for instance, a spark ignites a mixture of petrol vapours and air. This is possible because petrol is highly volatile and easily vaporuizes. Diesel cannot take the place of petrol here because it is less volatile. A different strategy is used in diesel engines. Here, the air is made hot by first compressing it. Diesel is then squirted into the hot air and it burns. Besides, the compression ratio, the difference between the pressure of the fully compressed fuel mixture and atmospheric pressure is much higher in a diesel engine. That is why; diesel cannot be used in place f petrol or vice versa.
When an empty metal vessel is struck, the entire surface of the vessel is set into vibration. The air in contact with the vessel is also set into vibration producing sound of high intensity. If the vessel is partly filled, the surface area of the vessel remaining free to vibrate becomes greatly reduced. Since the total area of air that is set into vibration by the vibrating surface of the vessel also becomes much smaller than in an empty vessel, the intensity of sound also gets reduced.
The earthing of electrical appliances is done as a safety measure. Most of the non-current-carrying metallic parts of an electrical appliance are well insulated and safe to use, but in a faulty appliance current can pass through even these insulated parts and pose a risk to the life of the user. This is because the human body allows an easy flow of electricity through itself to ground. The earthing of the appliances prevents this risk as the earth wire offers a still easier path compared to the human body to the flow of leaking current to ground, thus making the appliance safe to use.
It is easier to balance a long pole on the palm than a short stick because of the higher position of the centre of gravity in the former which normally lies near the middle. For balancing a long pole by holding it upright on its end on our palm what we try to do is to keep its centre of gravity right above the base. As long as the centre of gravity remains straight above the base, the stick remains balanced. But being unstable, it tends to fall and the centre of gravity moves away from the vertical. With a long pole we get sufficient time to move our hand to bring its base directly below its centre of gravity thus restoring balance. But with a short stick we hardly get any time to move our palm to restore the balance and the stick falls down.
A kite flies better without wobbling, spinning or diving if it can keep itself inclined at a specific angle against the blowing wind. This creates a difference in the air-pressure around the kite in such a way that the kite is lifted up. The tail helps a kite in keeping its angle of inclination stable by pulling down its lower tip. Without the tail, wind blowing against the kite and the lift-force generated in turn would send a conventional kite into a tail-spin. Box-kites, however, do not need a tail to stabilize as they do not need to maintain a constant facing angle against the wind to generate the lift. The air swirling through and about a box-kite creates all the pressure differences required to lift up.