Question

Give one method each to increase and decrease frictional force between two surfaces?​

Answer 1

Answer:

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• Use of lubricants: In machines, friction can be reduced by applying lubricants between the contact surfaces to fill the fine pores or depressions in the surfaces and make them smooth thereby reducing friction.

• Polishing : unevenness of the surfaces can be reduced by polishing, thereby reducing the friction.

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Answer 2

Method to increase frictional force :–

1. Increasing the roughness of surface – Friction can be increased by making the surface rough so that they have better grip on each other. For e.g.- the friction in the tyres of bicycles, cars, buses, and other vehicles is increased by making grooves in them.
2. Making use of different materials – Sometimes, we use different materials to increase friction. For e.g.- Wheels of a trolley have a rubber rims instead of metal to increase the friction. Legs of chairs and tables are fitted with rubber washers to have better grip on the floor.
3. Using dry surfaces – Friction can be increased by making the surface dry. For e.g.- a wet glass has tendency to slip more easily from our hands than a dry one.
4. Increasing the pressure of surfaces in contact – One can increase the friction by increasing pressure of surfaces in contact. For e.g.- when any object starts slipping from our hand, we hold it firmly bh applying more pressure which increases the friction between our hand and the object.

Methods to decrease frictional force :–

1. Polishing – Irregularities of the surfaces can be reduced by polishing or smoothening, thereby reducing the friction For e.g.- Highly polished metal sheets are used for piston and cylinders of an engine to reduce friction and in turn, increase efficiency of the engine.
2. Oiling or lubricating – the use of lubricants such as oils, grease, glycerine, graphite powder,etc., between two surfaces in contact reduces friction between them. For e.g.- a coin of carrom moves very easily on a powdered carrom-board. This is because the depressions on the surface of the board and coins get filled with powder and become smoother.
3. Use of wheels and ball-bearings – One can add rollers between the surfaces sliding together, to change the sliding friction into rolling friction. To move heavy bodies easily, we convert the sliding friction into rolling friction by making attachment of wheels to the bodies. For e.g.- people use heavy suitcase fitted with small wheels.
4. Streamlining the shape of bodies – To minimize the Friction dur to resistance of the medium (air/water) the bodies of aeroplanes, racing cars, missiles, rockets, ships, boats are streamlined by reducing the front surface of contact of objects with the medium.