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| Sunday, 20 February 2005 |
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Junior Observer |  |
| News Business Features Editorial
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How friction helps you Do you know what friction is? Friction is the force which slows down the motion of two objects that are rubbing against each other. It is the force of friction that slows a moving object and makes them come to a halt.
When you are riding your bicycle, you apply the brakes and the bicycle comes to a stop. This is also due to friction. When you apply the brakes, the brake blocks are pulled against the rim of the wheel and the friction between them causes the wheels to come to a halt. Did you know that friction causes heat ? You know that your hands would get warm if you rub them together. This is the result of friction. Also, when you strike a match on the side of a matchbox, friction between the two lets out heat which sets the chemicals in the matchhead alight. When objects such as space shuttles enter the atmosphere, they rub against the atmosphere which creates friction. The heat generated here could be as high as 1260 degrees Celsius. The special tiles which cover the outside of a space shuttle are there to protect the craft from this heat. Rough surfaces make more friction than smooth surfaces. You can examine this by taking a wooden plank and two wooden blocks, one rough and the other smooth. First, place the wooden plank on the ground, put the rough block on one end and start lifting that end while the other end of the wooden plank remains on the ground. In a while, the wooden block will start sliding down the plank. Then, place the smooth block on the plank and lift it up. The smooth block will start sliding down no sooner the plank is lifted, and the plank won't have to be lifted as high as before. It took more time for the rough block to slide down as the friction was much higher than with the smooth block. High friction and low friction both have their own benefits. For instance, rough tyres in vehicles are better than smooth tyres, because the former offers more friction. They have a better grip on the road. When brakes are applied, rough tyres will make the vehicle stop quickly whereas smooth tyres will skid on the road, leading to accidents. However, there are instances when the amount of friction has to be lessened. A door will squeak when it is opened, as parts of the door hinge rub against each other. If you put oil on the hinge, the parts will become smoother, friction will be less and the squeaking will stop. You may have noticed carrom players sprinkling talcum powder on the carrom board. This lessens the friction between the board and the discs, making the discs move faster. Ice floating on water When you put ice cubes into a glass of water or soft drink, you may have observed that the ice cubes remain on the surface without sinking to the bottom. You may be aware that cold water is heavier, but do you know how ice, which is another form of cold water, floats on water despite it being solid? As water gets colder, its volume decreases and it becomes heavier, but this process continues only upto a certain temperature which is four degrees centigrade. This is the temperature at which the density of water is maximum and the volume is minimum. When water takes the form of ice, its volume increases i.e. it covers more space in this form. The mass, however, remains unchanged when water is converted into ice. Neither is anything added nor taken away from it. So the mass remains unchanged while volume increases, which is quite apparent. It means that when water changes into ice, its density decreases. Anything which has a density less than the density of water, floats on water, and since the density of ice like that of wood and cork is less than the density of water, it too floats on water. There are various advantages as well as disadvantages of this phenomenon. In a very cold country, the river waters get frozen due to extremely low temperature. But, it is only the upper surface of the river that gets frozen and becomes solid. The water beneath it remains in liquid form, and thus the flora and fauna are saved from total annihilation. On the other hand, those who travel by sea can tell you the grave
dangers involved due to the large floating icebergs - the large chunks of
ice - in the sea. These icebergs, whose large parts are immersed in water,
could go underneath the ship, acting as sharp knives, cutting and damaging
the hull of the ship easily. |
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The baseball player in the picture is running into position. She rubs
against the ground to slow her down and get into the intended position.
Without friction, she would have slid right past this point. 
