Friction work against motion and produces heat that represents lost energy. And it happens whenever two objects come into contact or rub against each other. Because of friction, it’s impossible to realize the ideal mechanical advantage of a machine. Rough or malleable surfaces are more apt to produce friction, though even the smoothest surface creates some friction. The key to making a machine run as efficiently as possible is to minimize friction. Just as a greased pig is harder to catch, lubricated machine parts reduce friction and the wear that accompanies it. On the other hand, some devices- breaks, for example – actually use friction to work.
Ball bearings use the rolling action of balls to minimize friction between moving parts of a machine. Balls are mounted between grooved inner and outer rings called races. The inner ring is like an axle, and the outer ring simply rolls on its ball against the axle, it neither slips nor rubs. The spinning of skateboard and car wheels is made smoother by ball bearings. A good yo-yo contains a ball bearing that allows the outer part of the yo-yo to rotate evenly and with a minimum of friction around its axis. Ball bearings reduce the contact area between two metal surfaces to tiny points.
Even air creates friction when it rubs or pushes against an object’s surface and works against movement. The parachute harnesses this type of friction, known as air resistance.
As a parachutist leaps from an airplane thousands of feet above the ground, he or she will initially plummet with increasing velocity under the forces of gravity.
Then the parachute billows open. it is made of light-weight material originally linen or silk, now nylon to reduce the force of gravity on it but has a large canopy that maximizes its surface contact with the air. This contact slows the jumper’s descent to a safe landing speed.
Usually, when parts of a machine vibrate, they generate a sound we call noise. But in the case of a violin, our ears interpret string vibrations resonating in the instrument’s body as music. This vibration is caused by friction. In fact it results from oscillations in the force of friction called the stick slip phenomenon. The hairs of a bow drawn across a string alternate between pulling the string with it – sticking, in what’s called static frimtion – and, as the applied force overcomes static friction, slipping, in what’s called kinetic friction. The slipping friction is less than the sticking friction; this results in a sudden increase in the bow’s speed – a subtle jerking that vibrates the string. Horsehair has long been used in bows because its fibers have a propensity to grip the bow and hold the rosin that enhances stickiness.
A good swimmer seems to slip through the water, but water is denser and stickier than air, creating turbulence as it moves around the swimmer’s body as well as motion – opposing surface friction against the skin. Competitive swimwear has one overarching purpose: to minimize this drag.
What happens when drag – reducing swimwear begins to detract from the main event – the contest among the athletes themselves? It;s a question that came to the fore in 2008 with introduction of Speedo’s high – tech LZR Racer. The suit spawned a host of other shoulder – to – ankle, polyurethane based suits that compressed and streamlined the body as never before. The LZR Racer’s seams were even ultrasonically welded together rather than sewn , to minimize friction. The strategy evidently worked. At the 2008 Beijing Olympics, a great majority of medal-winning and record breaking swims were performed wearing the LZR. In 2010, the body that oversees officials international competition banned the suit and others like it.
Source : National Geographic